all

all

people

on both side of durand line in kabul plus khyber are

suffering

for no sin

of their

if the haves

continue this attitute

they

would

face elimination

at the hands

of world primitive

living

tribe

t6he puktoons

running

in tens of millions

on the same analogy that eliminated ussr

to rubbles out of which was born

russia

confusion and reality

United States Army IINTRODUCTION United States Army, military force of the United States with the chief responsibility for land combat. The U.S. Army includes the active-duty Army, the Army National Guard, Army Reserve, and civilian employees, all under the direction of the Department of the Army. The Army provides the forces stationed at permanent bases around the world and maintains combat-ready troops for deployment anywhere in the world. The Army National Guard and Army Reserve train units to provide emergency disaster assistance, to serve on active duty during wars, and to reinforce the main Army. The Army protects American interests by maintaining its standing force of about 487,000 soldiers, backed by about 200,000 troops in the Army Reserve and 350,000 in the Army National Guard. These troops are trained and equipped to destroy enemy armies and occupy other countries if necessary. Because of the Army’s ability to attack and control large geographic areas, it often becomes the decisive force in conventional (non-nuclear) conflicts. The Army works in concert with the three other major branches of the U.S. military—the Navy, the Marine Corps, and the Air Force. Navy ships transport Army troops, equipment, and supplies to bases overseas. The Navy also assists Army operations with air support, reconnaissance, and naval bombardments. Marine units conduct amphibious landings against defended shorelines and carry out conventional ground combat operations. The Air Force provides airborne transportation for Army units and offers other types of air support as necessary. The Army assists the other three branches by establishing and defending ground bases, communications facilities, and supply lines. IISTRATEGIC ROLE United States Army units stationed overseas protect America’s strategic interests, offer symbolic support for allied countries, and deter military aggression. The Army permanently stations about 65,000 soldiers in the Federal Republic of Germany and about 40,000 soldiers in South Korea. Following the U.S.-led invasion of Iraq in 2003, Army units were expected to remain in that country until a new civilian government could be established. The Army had about 120,000 troops stationed in Iraq as of 2005. The Army’s 25th Infantry Division also supplied the bulk of the nearly 18,000 soldiers stationed in Afghanistan in 2005. U.S.-led forces toppled the Taliban government there in 2001. The Army also deploys troops in about 100 countries at any given time to provide training and military education. To retain maximum flexibility to fight all over the world, the Army maintains combat equipment at strategic land bases around the world. The Army also keeps combat equipment on ships, called Maritime Prepositioning Ships (MPS), stationed in places such as the Persian Gulf and Diego Garcia, a small island in the Indian Ocean. If fighting seems likely, this equipment can be rapidly sent to the contested area. Army soldiers, rushed in on large transport planes, then unload the weapons and supplies from the ships and embark on their mission. In addition to the conventional combat forces, the Army also maintains Special Operations forces for quick deployment. Special Operations forces are exceptionally well-trained in weaponry, unconventional warfare, foreign languages, foreign cultures and ideology, and communications and electronics. The Army sends Special Operations forces on high-risk missions, such as attacking bases behind enemy lines, destroying enemy command posts, and long-range reconnaissance. IIIORGANIZATION The Army is organized into large fighting units called divisions. As of 2003 the main combat power of the Army had ten active divisions and eight reserve divisions, each containing from 13,000 to 16,000 soldiers. Each division includes supply, communications, and other support units so that it can operate independently from other Army units. The Army’s active force centers on six “heavy” divisions, which fight with tanks, infantry fighting vehicles, and other armored vehicles. The active force also includes an airborne division that can send paratroopers (soldiers trained to go into battle by parachute) to targets anywhere in the world, and an air assault division that uses helicopters to attack targets and deploy troops. Two more divisions are made up of light infantry—primarily foot soldiers with light weapons. The Army National Guard can mobilize eight additional divisions in time of war. Every division is divided into three or more combat brigades or regiments, each with 3,000 to 5,000 soldiers. Divisions also contain supporting units of many sizes, including military police, engineers, and command support staff. Each brigade contains three to five battalions of 500 to 1,200 soldiers. The battalion has three or more companies, which are sometimes called batteries (in artillery units) or troops (in cavalry units). Each company has about 150 soldiers, organized into platoons of about 40 soldiers. A platoon has three or four squads. With nine soldiers, the squad is the Army’s smallest unit. Below the division level, all Army units have a specialty, such as combat, engineering, intelligence, and artillery. IVCOMBAT EFFECTIVENESS The U.S. Army ranks behind many countries in the number of soldiers on active duty. However, its advantages in mobility, equipment, and training make it the most formidable ground force in the world. Compared to other armies, the U.S. Army has superior technology, highlighted by its precision weaponry and advanced communications capabilities. For example, the Army's M1 Abrams tank, with its computer firing controls, can accurately fire on targets even while moving, enabling it to take on and destroy several enemy tanks at once. The complexity of the weapons means the Army assumes a heavy supply and maintenance burden, but this characteristic is compensated for by the weapons’ battlefield effectiveness. Heavy divisions fight primarily with the M1 Abrams tank and the M2/M3 Bradley infantry-fighting vehicle. The principal weapon for an air assault division is the AH-64 Apache attack helicopter. Other combat units use the Artillery Multiple Launch Rocket Systems (MLRS), 155mm howitzers, Patriot antiaircraft missiles, portable Stinger antiaircraft missiles, and wire-guided antitank missile launchers. Most infantry soldiers carry the M16 assault rifle. The infantry may also use heavier weapons such as the M203 40mm grenade launcher, the M-249 5.56mm squad automatic weapon (a light machine gun), and the M-60 7.62mm machine gun. The airlift and sealift support of the U.S. Air Force and U.S. Navy gives the Army the greatest mobility of any army in the world. The Army can deploy the 82nd Airborne Division in just hours and provide reinforcements by a heavy brigade in about 15 days, or much sooner if the Army uses its prepositioned heavy equipment. In addition, the Army’s Special Operations and Airborne units can forcibly clear the way for larger Army deployments virtually anywhere in the world. The Army’s experience in the years after the end of the Cold War in 1991 revealed a need for improved strategic responsiveness. During the conflict in Kosovo in 1999, for example, the Army appeared to be slow in putting ground forces quickly into position for possible deployment. To be able to deploy rapidly around the world the Army needed to develop lighter equipment that could be transported more quickly. Enhanced strategic responsiveness required reduced demands for logistics support, such as fuel, ammunition, and repair parts. The need for quick deployment led the Army to develop a lighter, wheeled infantry-fighting vehicle called the Stryker, which currently is being used in two infantry brigades and which will be used eventually in up to six Army combat brigades. The Army also initiated a research program to develop a new combat system to replace the M1 tank and the M2 Bradley fighting vehicle with a system that will be effective in combat but weigh considerably less. In addition to its technological sophistication, the U.S. Army maintains combat readiness through realistic and comprehensive training at every level—from the individual soldier through the division. Active units routinely train at three of the world’s most comprehensive combat training centers: the National Training Center near Barstow, California; the Joint Readiness Training Center near Leesville, Louisiana; and the Combat Maneuver Training Center at Hoenfels, Germany. These “instrumented battlefields” can measure with precision the outcomes of mock battles. In addition to these major training centers, extensive computer simulation systems make it possible to train individuals, crews, and combat units in complex scenarios. The Army’s superior mobility, technical sophistication, and training do not guarantee success on the battlefield, but they provide a substantial advantage in most conflicts. VTHE LIFE OF A SOLDIER ARecruitment The U.S. military, including the U.S. Army, is a volunteer force. It does not currently use conscription (forced military service, also known as the draft). In 2003 over 95 percent of new enlistees in the U.S. Army were high school graduates. Some joined the Army to take advantage of college scholarships funded in part by the Army after their term of service, but many others joined to serve their country for longer periods. Recruiting offices throughout the country help persuade young people to consider a career in the military. After enlistment, new soldiers are sent to basic soldier training, which is called boot camp because new recruits were once known as boots. After basic training, soldiers train in their military occupational specialty (MOS) and are assigned to a unit. In 2003, 15 percent of the enlisted soldiers in the Army were women. Officers of the Regular Army—the Army’s permanent force—must have a college education and are appointed from one of three sources. Enlisted soldiers with college degrees may become officers by attending Officer Candidate School (OCS). Alternatively, some officers receive their commissions (formal award of rank) through the Reserve Officer Training Corps (ROTC) programs at over 250 colleges and universities around the country. A select few young men and women attend the United States Military Academy at West Point, New York, which offers an intensive four-year college-level program with rigorous military training and traditional academic subjects. All newly commissioned officers receive the rank of second lieutenant. All soldiers, officer and enlisted, are assigned to one of 21 branches according to the functions they will perform in combat or in support of combat units. The main combat branches are infantry, armor, field artillery, aviation, and engineers. Enlistees can request assignments from over 200 military occupational specialties associated with the various branches. Women are excluded from combat specialties, and this limitation includes complete exclusion from infantry and armor branches as well as from most field artillery and combat engineer specialties. Women have increasingly demanded that the Army open all positions to women, and this pressure for change has been controversial both within the Army and in the United States as a whole. Homosexuals can serve in the Army, but they must conform to the U.S. military’s “don’t ask, don’t tell” policy. Under this policy, homosexuals will not be sought out for expulsion from the Army, but they may be forced to leave the service if their sexual orientation becomes known. BTraining When not at war soldiers spend most of their time preparing for war. From the moment a soldier enters the service, constant attention is paid to physical fitness. Physical training (PT) is the foundation for preparing soldiers for the stresses likely to be encountered in battle. Physical training includes running, group exercises, and sports and other physical fitness events. At their home military bases, soldiers spend most days training for wartime missions. This regime includes training on combat skills in classrooms, in nearby training grounds, and at special sites where combat equipment is stored. Training exercises may last a few days or several weeks. Units routinely go to other military bases or the combat training centers in California, Louisiana, or Germany to practice combat skills in different settings. Soldiers concentrate on proficiency at operating their weapons and on coordinating their efforts with the squad, platoon, and company. In addition to field training, officers and enlisted soldiers spend considerable time in the classroom. Enlisted soldiers attend a series of schools as they move up the ranks. Immediately after their commission, officers attend a training course in their branch of the Army. They take an advanced course in their branch specialty five years later. Officers with the rank of major attend the Command and General Staff College at Ft. Leavenworth, Kansas, and later, after obtaining the rank of colonel, the Army War College at Carlisle Barracks, Pennsylvania. Continuing education is a central part of the Army’s leadership development program. During deployments, whether for training or actual fighting, soldiers usually live in tents or in their vehicles. In the field they usually eat prepackaged rations called meals ready to eat (MRE). The Army also has contracted with private companies to provide hot meals to soldiers who are in the field or deployed to foreign countries such as Kuwait. Most units also have cooks who make one or two hot meals a day. To assist with meal cleanup, some junior soldiers (privates or specialists) are occasionally assigned to pot scrubbing and other time-consuming chores. Most soldiers dislike this assignment, which is sometimes called the kitchen police, or KP duty. At permanent bases civilian employees do this work. VIHISTORY The Continental Congress created the United States Army on June 14, 1775, in the midst of the American Revolution (1775-1783). Some National Guard units trace their ties to pre-Revolutionary War colonial militia units. Since 1775 Army soldiers have fought and died in every American war. The Army flag has 176 campaign streamers attached, each one marking a major milestone in Army history. These landmarks of American military history include Lexington, Yorktown, New Orleans, Sumter, Gettysburg, Appomattox, Little Bighorn, Meuse-Argonne, Guadalcanal, Normandy, Korea, and Tet. Until the end of World War II (1939-1945), Congress usually reduced the size of the Army to a bare minimum between wars. This practice resulted from the country’s distrust of standing armies that dates to colonial times. At the outbreak of war, the opening stages for the Army were characterized by a massive effort to mobilize and train the masses of soldiers needed for war. Since World War II, however, the United States has maintained a substantial permanent Army. In addition to foreign wars, the Army has conducted many missions on American soil, including disaster relief, frontier patrol, and the major engineering projects of the U.S. Army Corps of Engineers. Outside the United States, the Army has been involved in many operations other than war, including peacekeeping missions, disaster relief, and humanitarian assistance. The Army has also conducted many small-scale combat missions, such as during the 1900 Boxer Uprising in China and a 1918 mission in Russia. Presidents George Washington, Andrew Jackson, Ulysses S. Grant, William H. Harrison, Zachary Taylor, and Dwight D. Eisenhower had extensive careers as Army officers. Other presidents, such as Rutherford B. Hayes, William McKinley, Theodore Roosevelt, and Harry S. Truman served as Army officers in time of war. Other famous Army leaders include Henry Knox, Winfield Scott, John Pershing, Douglas MacArthur, Omar Bradley, Norman Schwarzkopf, and Colin Powell. AAmerican Revolution The Army faced long odds in the American Revolution (1775-1783), which began in 1775 when American colonists demanded independence from Britain. The British army was larger, better equipped, and backed by the world’s most powerful navy. German mercenaries known as Hessians bolstered the size of the British force. The colonials’ main force, the Continental Army, consisted mainly of inexperienced, poorly equipped volunteers who had joined in response to an offer of a cash bonus and a promise of land after the war. The states refused most of the Continental Congress’s requests to provide money and supplies for the troops. Local militias reinforced the Continental Army. Many militia soldiers were experienced and better equipped than their Continental Army counterparts, but they were generally not prepared to fight far from home or for extended periods. The weakness of the combined militia and the Continental Army left General George Washington few options at the outset of the war. Washington’s forces fought well in localized battles and skirmishes, but had far less success waging sustained offensive maneuvers. By the summer of 1776, the American troops struggled for survival against a skillful British offensive in New York and New Jersey. The Continental Army won few significant battles until late in 1776, when Washington made his famous Christmas night crossing of the Delaware River to surprise British forces in Trenton, New Jersey. Through the next several years, Washington gained the upper hand over the British by avoiding direct confrontations, focusing instead on stealth and surprise to weaken the enemy. The success of the Continental Army and local militias brought the French into the war as an American ally, and eventually forced the British to agree to the colonials’ demands for independence in 1783. About 4,000 soldiers died in the war. See American Revolution. After the American Revolution Congress disbanded most of the Army, and in 1789 it stood at just 800 soldiers. Local militias assumed most military duties, primarily fighting Native Americans as wars accompanied westward settlement into the Ohio Valley, Kentucky, and Tennessee. In 1802 Thomas Jefferson founded the United States Military Academy at West Point. Workers built it on the site of one of George Washington’s most valuable Revolutionary War outposts. The U.S. Military Academy has produced many of the nation’s most famous military leaders, including United States presidents Ulysses S. Grant and Dwight D. Eisenhower. BWar of 1812 In the late 18th and early 19th centuries many European countries fought in the Napoleonic Wars (1799-1815). The United States became entangled in the conflict in 1812, after both England and France had seized a total of over 1,000 American merchant ships. The United States declared war on England in 1812 in an effort to protect its trade rights and to oust British forces from Canada, their last stronghold in North America. Small, disorganized, and poorly trained combinations of American regulars and militia traded blows with the British, but could not win control of Canada. In 1814 improved American forces claimed a victory at Chippewa, in what is now Ontario, Canada. Early in 1815, soldiers under the leadership of future president Andrew Jackson defeated the British in the Battle of New Orleans. Both sides wearied of the fighting, and Jackson’s battle marked the last in the war. Militarily, the war produced no significant changes, and Canada remained firmly in British hands. (See War of 1812.) CMexican War By the 1840s the United States Army was small but relatively professional. The westward expansion of the United States led to war with Mexico in 1846. The Mexican War (1846-1848) marked the first time the Army fought a war primarily on foreign soil. Despite being outnumbered by Mexican forces in most engagements, the U.S. Army maintained an advantage through the use of speedy breech-loading rifles, withering artillery attacks, and superior battlefield tactics. By 1847 the Army controlled much of the Mexican interior, and in August of that year U.S. forces moved into Mexico City and occupied it. Mexico soon admitted defeat and agreed to a peace settlement in which it gave up about half of its territory to the United States. About 1,700 American soldiers died in the fighting. Among the U.S. troops were two young officers, Robert E. Lee and Ulysses S. Grant, who both later rose to top ranks in the Army. DCivil War and Late 19th Century The American Civil War (1861-1865) pitted Lee, Grant, and many other experienced members of the Army against each other. Civil War battles rapidly overshadowed all previous combat in American history with their unprecedented levels of death and destruction. Technical improvements in both rifles and artillery led to extraordinary casualties for Union and Confederate forces. Both types of weapons were rifled (made with spirals engraved in the barrels) to increase range and accuracy. At the Battle of Shiloh in 1862, the Union Army lost more than 10,000 soldiers in two days of fighting, more than had died in the eight-year American Revolution. Historians do not know exactly how many soldiers of the Union and Confederate armies died by the end of the Civil War in 1865, but the total exceeded 600,000. This total is more than the combined number of American deaths in all other U.S. wars from the American Revolution through the war in Afghanistan in 2001. The Civil War was the Army’s first war of the industrial era. Both Union and Confederate forces relied on railroads to move soldiers and equipment, and used the improved firepower of factory-produced weapons. Telegraph lines carried battle orders and reports of damage, and the North’s blockade of the South meant that no part of the Southern economy remained unaffected by the conflict. Conscription helped both sides create huge armies. After the Civil War the Army occupied the former Confederate states as part of Reconstruction—the process of rebuilding the South. This mission pitted the Army against the Ku Klux Klan and other white-supremacist resistance groups. Reconstruction came to an end in the late 1870s, and federal troops were withdrawn. In the years following the Civil War, the Army also expanded its campaign against Native Americans as settlers moved west and pushed them off their lands. The most famous battles took place on the Great Plains, where the Sioux, Cheyennes, Comanches, Kiowas, and others fought the Army from 1855 to 1877.The most notable encounter was the defeat of Lieutenant Colonel George Custer’s command at the Battle of the Little Bighorn in southern Montana in 1876. By the 1890s the American frontier was gone, and the Native Americans had been subdued. The closing of the frontier ended the mission that had defined the Regular Army for most of its existence. ESpanish-American War and Philippine Insurrection The search for new markets for American business interests at the turn of the 20th century helped spur the United States to declare war on Spain in 1898. During the war the American military took control of Cuba, Puerto Rico, and the Philippines. The war lacked notable land battles, apart from the famous exploits of the Rough Riders led by Theodore Roosevelt, who would become president three years later. The war marked the Army’s first major mobilization and deployment off the American mainland. The fighting with Spain lasted less than four months. Few U.S. Army soldiers died in battle, but several thousand perished from disease and poor sanitation. In the Philippines, guerrilla resistance occupied the Army for several years of intense battles from 1899 to 1901. Sporadic fighting in the Philippines continued over the next ten years. (See Spanish-American War.) FEarly 20th Century The early 20th century brought significant change to the Army. The Department of War, later renamed the Department of Defense, created the Army War College in 1901 to train the Army’s senior officers. In 1907 the Army established the Army Air Corps to explore the military use of airplanes, dirigibles, and other aircraft. The Army Corps of Engineers supervised the construction of the Panama Canal beginning in 1907. Under the leadership of Colonel George W. Goethals, the Army engineers completed work on the 82-km (50-mi) waterway in 1914, one of their most notable peacetime projects. The Army also made construction of the canal possible through improved public health in the Canal Zone. Tropical diseases had stymied previous canal construction efforts. Army sanitary officer William Gorgas brought malaria and yellow fever under control, protecting canal workers from these deadly diseases. GWorld War I (1914-1918) The United States stayed on the sidelines of World War I until Germany’s unrestricted submarine warfare drew the country into the conflict in 1917. The U.S. Army deployed hundreds of thousands of troops to France to join the Allied efforts to defeat the German empire. The relatively fresh Americans helped turn the tide against the Germans. By the time Germany capitulated in 1918, over 4 million soldiers had served in the U.S. Army, and more than 50,000 had died in battle. The war demonstrated that heavy artillery, machine guns, tanks, flame-throwers, and other weapons had rendered many traditional tactics obsolete. The Army Air Corps, the forerunner of the U.S. Air Force, proved the potential of combat aircraft. World War I also marked the largest U.S. military mobilization up to that time, and required a massive shift in industrial production to support the millions of soldiers. The Army’s success in battle became closely tied to the efficiency of industry, agriculture, and most other sectors of the economy at home. After the war, the United States rapidly demobilized and reduced the Army to a force of less than 100,000 soldiers. In the following years, this small force underwent tremendous change as it incorporated into its operations the rapid technological advancements in aircraft and armored vehicles. On the ground, horse-mounted cavalry gave way to soldiers mounted in tanks. In the air, crude and flimsy biplanes gave way to increasingly powerful fighters and bombers capable of long-range attack deep behind enemy lines. HWorld War II (1939-1945) The United States began to increase military spending in the late 1930s and 1940s, but the country was not ready for war when the Japanese attacked Pearl Harbor on December 7, 1941. The attack shocked the country and brought the United States into the war. Millions of men volunteered for the Army and other branches of the military. Congress also conscripted millions of men into the Army. The Army relied heavily on air power during World War II. The Army Air Corps used heavy bombers to strike civilian and military targets deep behind enemy lines. Newly developed fighter airplanes supported frontline soldiers with close air support—attacks on enemy ground positions. On the ground, the Army conducted amphibious assaults throughout Europe and the Pacific, including difficult landings at North Africa, Sicily, Normandy, the Philippines, and Okinawa. In Burma (now Myanmar) and other parts of the Pacific theater, Army units fought their way through jungle and swamps in slow-moving infantry battles. The relatively open terrain in Europe made it possible to deploy large columns of tanks. Army commanders such as General George Patton mounted aggressive tank assaults to lead U.S. forces. Combined with infantry, artillery, and close air support, the effective use of armor helped overpower enemy defenses. World War II also saw the widespread use of air transport to deliver Army soldiers to the battlefield. In some major attacks, Army forces parachuted into position. The most notable airborne action was the massive paratroop support of the D-Day landings in the Normandy region of France in June 1944. As in World War I, American industrial power and mass mobilization provided the military capabilities, supplies, and equipment essential for American victory in World War II. At its peak in World War II, the U.S. Army had more than 8.2 million soldiers. More than 230,000 Army soldiers died in combat. ICold War Years After the war, the U.S. Army occupied and governed Germany and Japan. In 1947 the Army Air Corps officially split from the Army to become the United States Air Force. The advent of nuclear weapons at the end of World War II convinced some strategists that ground combat forces would become far less important. But the Army’s ground units turned out to be key elements throughout the Cold War, during which the United States and its allies struggled for global power against the Union of Soviet Socialist Republics (USSR) and its allies. Most Army soldiers returned to civilian life after World War II, so the Army was caught off guard when North Korea (Democratic People’s Republic of Korea) invaded South Korea (Republic of Korea) in June 1950, starting the Korean War (1950-1953). Fearing that the attack by Communist North Korea could lead to Communist gains elsewhere in Asia, President Harry Truman sent Army troops to fight in the war. Although formally a United Nations (UN) undertaking, the Korean operation was led by the U.S. Army. The hastily assembled UN forces suffered setbacks in the early months of the war, but regained the initiative with a surprise landing behind enemy lines at Incheon in September 1950. The dramatic amphibious assault, directed by General Douglas MacArthur, enabled the United States and its allies to recover the territory of South Korea that had been lost to the North Koreans. The UN forces pushed north into North Korea toward the Yalu River that borders China. In late November and early December 1950 China responded, sending hundreds of thousands of soldiers to fight alongside the North Koreans. The UN forces were soon bogged down in a long and costly stalemate on the ground. An armistice ended the war in 1953 after more than 27,000 Army soldiers died in battle, out of a total of more than 2 million who served in the Army during the war. The United States has stationed Army troops in South Korea ever since. In the aftermath of the Korean War, the United States maintained the largest peacetime Army in the country’s history. For the first time, the U.S. Army stationed large numbers of soldiers overseas, particularly in Germany and South Korea. In Germany, some of these bases served as a “tripwire,” putting American forces in the front lines of any possible Soviet attack. This positioning assured American allies that the U.S. soldiers would face combat in the early stages of a Soviet invasion, thereby raising fears in the minds of Soviet leaders that American political and military leaders would be more likely to use nuclear weapons to repel the Soviets. Similarly, by putting U.S. troops along the border of South Korea and North Korea, the United States signaled that it would use force to defend South Korea. JVietnam War (1959-1975) American involvement in the Vietnam War dates to the 1950s, but became substantial only in 1961 when President John F. Kennedy sent a large contingent of U.S. Army Special Forces (Green Berets) to support the South Vietnamese Army. By 1963 the number of Green Berets and other “advisers” passed 16,000, and some were involved in combat. Kennedy was assassinated in November 1963. His successor, President Lyndon Johnson, dramatically increased the number of troops in Vietnam in 1964. The Army relied on technological sophistication and massive firepower to fight the North Vietnamese army and guerrilla forces. The major military innovation of the Vietnam War was the advent of air mobility—the use of helicopters to transport soldiers and supplies in and out of battle, despite difficult terrain. Helicopters also ferried the wounded away from the battlefields, making it much more likely that these soldiers would survive. The North Vietnamese forces had far less sophisticated weapons and equipment than the Americans but used hit-and-run tactics with devastating effect. By avoiding most pitched battles with American troops, the North Vietnamese undercut the U.S. Army’s advantage in firepower. American public support for the war withered as U.S. losses mounted in the late 1960s. The calls for U.S. withdrawal became even more intense in 1969 when the press reported details of the My Lai Massacre, in which U.S. Army troops killed from 300 to 500 unarmed civilians. President Richard Nixon began withdrawing American forces in the early 1970s, and the last soldiers left in 1973. At the height of the war, the Army had nearly 500,000 soldiers assigned in Vietnam. Over 30,000 Army soldiers lost their lives in combat. KLate 1970s and 1980s After the demoralizing defeat in Vietnam, American leaders became reluctant to send troops into combat. The Army remained a central element of the U.S. military strategy against the Soviet Union, however. Other branches of the military controlled most of the strategic nuclear weapons powerful enough to destroy very large targets. The Army’s strategy emphasized the use of tactical nuclear weapons—those that can be used to attack battlefield targets. The Army’s nuclear arsenal included thousands of atomic artillery shells for repelling a potential Soviet attack in Europe, although many experts doubted that the radiation from these weapons could be confined to enemy targets. The Army also reacted to the Soviet threat by developing new heavy armor, including the M1 Abrams tank and the M2 Bradley fighting vehicle. The M1 was designed to destroy the Soviet army’s T-80 tanks if they tried to invade Western Europe. The Army invested heavily in building the Abrams to be faster and more lethal than its predecessors so that it could fight the more numerous Soviet tanks. The Abrams met these objectives, but it also used more than twice as much fuel as its predecessor and required more maintenance on its advanced engine and weapons systems. The Army developed the Bradley fighting vehicle to carry infantry into battle alongside the Abrams. In addition to its crew of three, each Bradley can carry six soldiers, and it can match the Abrams’s speed. In order to make the Bradley fast enough to keep up with the Abrams, designers used light but relatively soft aluminum armor on the vehicle, raising concerns that they would not survive combat with enemy armored vehicles. The Bradley also boasts substantial offensive firepower, including antitank missiles and a 25mm gun with a sophisticated thermal sight that allows the gunner to aim through darkness, dust, or smoke. Again, the sophistication of the thermal sight and other equipment on the Bradley substantially increased maintenance requirements. LPost-Cold War The collapse of the Soviet Union in 1991 forced the Army to rethink its overall global strategy. Facing a relatively weak Russian army, there was no longer a pressing need to train and plan for a massive ground war in Europe. In the early 1990s the Army began to reduce its soldier ranks by about one-third in order to pay for operations and readiness requirements and to provide modest funding for modernization of some parts of the Army. The Army also removed all nuclear weapons from its inventory. The United States developed a new global strategy based on the assumption that it would be forced to fight two major regional conflicts simultaneously. This strategy also assumed that while fighting the two wars, the Army would also be responsible for operations other than war, such as peacekeeping missions abroad and disaster relief at home. This strategy called for the continued deployment of soldiers in Germany and South Korea, and for heavy reliance on equipment and supplies on the strategically located Maritime Prepositioning Ships. The Persian Gulf War (1991) presented the Army with a significant challenge. The Iraqi invasion of Kuwait in August 1990 led President George H. W. Bush to send hundreds of thousands of Army soldiers to turn back the invasion, supported by a United Nations (UN) resolution calling for Iraq to withdraw. In January 1991 aircraft led by the United States conducted over 100,000 bombing runs against Iraqi targets. The next month the U.S. Army took the lead in the largest armored battle since World War II. With almost half a million American soldiers operating in conjunction with the other U.S. military services and units from allied nations, the Army played a key part in the successful 100-hour ground campaign that forced Iraq to surrender. From 1991 to 2001 the Army conducted a number of humanitarian and peacekeeping missions abroad, in countries such as Bosnia, Haiti, Rwanda, the Former Yugoslav Republic of Macedonia, Somalia, and Kosovo. The Army faces a quandary in responding to such international crises. Many Americans recoil at televised images of hunger and war abroad, and support the deployment of U.S. troops to deliver aid. At the same time, however, public support for these humanitarian missions can dissipate quickly when American lives are lost. The 1999 military campaign in Kosovo relied almost exclusively on air power to avoid ground combat casualties. MGlobal War on Terrorism Following the terrorist attacks on the United States on September 11, 2001, U.S. Army soldiers were deployed to Afghanistan to engage the al-Qaeda terrorists who were behind the attacks and the Taliban government that supported them. At first, most of the American soldiers were Special Forces (Green Berets) who trained Afghans to fight against the Taliban and al-Qaeda. These Special Forces soldiers, sometimes riding on horseback with Afghan men, used modern satellite communications to direct precision weapons dropped from airplanes or unmanned aerial vehicles against Taliban forces. After the Taliban government was ousted, regular Army combat units were deployed to Afghanistan to conduct operations against remnants of the Taliban government and al-Qaeda. The rugged mountainous terrain and harsh climate made combat operations difficult, because the terrain provided an almost endless number of places for the Taliban and al-Qaeda to hide and reduced the effectiveness of U.S. advantages in mobility, firepower, and communications. As part of the fighting against terrorists, U.S. Army soldiers were also deployed to a number of other countries, including Uzbekistan, Kyrgyzstan, and Tajikistan. Army soldiers also were sent to Yemen, Somalia, the Philippines, and the country of Georgia to help train local forces in antiterrorism measures. After the September 11 attacks more than 40,000 Army National Guard and Army Reserve soldiers were called up for active duty. Some of these soldiers were deployed overseas, while others were assigned to protect vulnerable targets in the United States, such as airports and national landmarks, and to augment security forces at Army installations throughout the United States. Soldiers are expected to be engaged for the foreseeable future in such homeland defense operations, especially soldiers in the National Guard, which has units in all 50 states. NInvasion of Iraq In late March 2003 the U.S. Army took part in an invasion of Iraq to depose the regime of President Saddam Hussein, who was suspected of concealing weapons of mass destruction. After less than a month of fighting, U.S.-led forces were in control of all the major cities and oil fields of Iraq, including the capital Baghdād. The U.S. Army’s 3rd Infantry Division played a key role in capturing the capital, while the 101st Airborne Division captured oil fields and other major urban areas. Iraqi infantry and armored forces were unable to mount effective resistance to U.S. Army tanks and other armored vehicles. United States forces suffered a total of 138 deaths from March 19 through April 30. On May 1 President George W. Bush declared an end to major combat operations. However, in the ensuing years, an insurgency in Iraq killed more U.S. troops than died during the invasion of Iraq and the capture of Baghdād. The U.S. Army faced urban guerrilla warfare that featured roadside bombings, ambushes with rocket-propelled grenades, and mortar attacks.

http://hayatashah.multiply.com

hi n good wishes

its the 21st june and it would bve 23rd june on monday thereby changing the long days to shorten untill 22 decenber

have a great weekend

regards

just for all who visit and thanks

its been quite difficult these days to have electricity most of the times in office or home

the blogging and netsurfing that i used to do on regular bsis besides upadting of downloads from microsoft has also been affected by the power/electric current

othar than the above two reasons its quite hot also and prices gone up with rise in crude oil prices touching 140$

enjoy

regards bestwishes

its hot and the power goes off mostly

so lets enjoy the heat than

hi

sorry for being giving little time
here
have a great
time

civilizations

Indus Valley Civilization

I

INTRODUCTION

Indus Valley Civilization

In the Indus valley area now known as Pakistan, an advanced Bronze Age culture rose up about 2500 bc and lasted for nearly 1000 years. Scholars do not know how it began or whether its people were related to those who now occupy Southwest Asia. Nomadic tribes called Aryans invaded the Indus River valley, probably from the region north of the Caspian Sea, in 1500 bc. The Aryan culture became dominant in the area, eclipsing that of its predecessors.

© Microsoft Corporation. All Rights Reserved.

Indus Valley Civilization (2500?-1700 bc), earliest known civilization of South Asia, corresponding to the Bronze Age cultures of ancient Egypt, Mesopotamia, and Crete (Kríti). The remains of settlements belonging to this culture have been found throughout the Indus River valley in Pakistan, westward along the coast to the Iranian border, in India's northwestern states as far east as New Delhi, and on the Oxus River in northern Afghanistan. The Indus Valley civilization encompasses one of the largest geographical areas covered by a single Bronze Age culture.

II

CHARACTERISTICS

Indus Valley Art

The Indus Valley civilization thrived in the area of present-day Pakistan and western India between about 2500 and 1700 bc. A farming community, the civilization created artwork associated with agricultural life. Found at the archaeological site of Mohenjo-Daro, this ceramic figure depicts two oxen pulling a woman in a cart.

Scala/Art Resource, NY

Excavated settlements reveal blocks of mud-brick buildings separated by streets, and the cities, such as Mohenjo-Daro and Harappā, are dominated by large public buildings. These buildings were at one time identified as colleges, temples, granaries, and palaces, but later research has not confirmed such interpretations. The cities are usually divided into two distinctive groups of buildings, one of which may be enclosed by a wall.

The work of Indus Valley artisans shows a high degree of craft specialization. Characteristic artifacts include a distinctive black-on-red pottery, ceramic toys and figurines, etched carnelian beads, metal (bronze, silver, and gold) ornaments and tools, and stamp seals with an undeciphered script. Unfortunately, the nature of the social organization in this complex culture still evades complete interpretation.

Sometime after 2000 bc, complex ecological changes occurred in the Indus Valley area, forcing abandonment of many settlements and altering the basic characteristics of the civilization. Late Indus Valley culture is known mainly from excavated small farming villages. Artifacts associated with these sites are stylistically similar to earlier types but show more regional variation.

III

HISTORY OF EXCAVATIONS

Stone Tablets from Mohenjo-Daro

These stone tablets were found at Mohenjo-Daro, an archaeological site in modern Pakistan. The city of Mohenjo-Daro flourished during the Indus Valley civilization (2500?-1700 bc). Merchants use the stone tablets, which show examples of pictographic writing, to mark their goods.

Charles and Josette Lenars/Corbis

The Indus Valley civilization was first defined by the British archaeologist Sir John Marshall's diggings at Mohenjo-Daro and M. S. Vat's excavations at Harappā (both in what is now Pakistan) in the 1920s, and it is sometimes called Harappān civilization after the latter site. In 1946 the British archaeologist Sir Mortimer Wheeler, excavating at Harappā, located stylistically different pottery in the earliest occupied areas. Subsequent discoveries at nearby Kot Diji established that this early pottery at Harappā belonged to the early Bronze Age Kot Diji culture. Since 1960 Indian, Pakistani, and Western scholars have defined several additional early Bronze Age cultures at Goth Āmri, Sothi, Gumla, and other sites in Pakistan, each of which has some traits in common and contributed to the formation of the Indus Valley civilization.

countries

Afghanistan Facts and Figures

Basic Facts
Official name	Islamic Republic of Afghanistan
Capital	Kabul
Area	652,225 sq km
	251,825 sq mi
People
Population	31,056,997 (2006 estimate)
Population growth
Population growth rate	2.67 percent (2006 estimate)
Projected population in 2025	50,252,227 (2006 estimate)
Projected population in 2050	81,933,479 (2006 estimate)
Population density	48 persons per sq km (2006 estimate)
	124 persons per sq mi (2006 estimate)
Urban/rural distribution
Share urban	23 percent (2003 estimate)
Share rural	77 percent (2003 estimate)
Largest cities, with population
Kabul	2,678,000 (2003 estimate)
Kandahār	225,500 (1988 estimate)
Herāt	177,300 (1988 estimate)
Ethnic groups
Pashtun	38 percent
Tajik	25 percent
Hazara	19 percent
Minor ethnic groups (Chahar Aimaks, Turkmen, Baluchi, Nuristani, and others)	12 percent
Uzbek	6 percent
Languages
Afghan Persian (Dari)	50 percent
Pashto	35 percent
Turkic languages (primarily Uzbek and Turkmen)	11 percent
30 minor languages (primarily Balochi and Pashai)	4 percent
Many people are multilingual
Religious affiliations
Sunni Muslim	84 percent
Shia Muslim	15 percent
Other	1 percent
Health and Education
Life expectancy
Total	43.3 years (2006 estimate)
Female	43.5 years (2006 estimate)
Male	43.2 years (2006 estimate)
Infant mortality rate	160 deaths per 1,000 live births (2006 estimate)
Population per physician	5,381 people (2004)
Population per hospital bed	2,500 people (2001)
Literacy rate
Total	36.3 percent (2000)
Female	20.8 percent (2000)
Male	51 percent (2000)
Education expenditure as a share of gross national product (GNP)	2 percent (1980)
Number of years of compulsory schooling	6 years (2002-2003)
Number of students per teacher, primary school	61 students per teacher (2002-2003)
Government
Form of government	Islamic state; transitional government
Voting qualifications	18 years of age; universal
Constitution	In January 2004 the loya jirga ratified a new constitution
Armed forces
Total number of military personnel	Undetermined
Military expenditures as a share of gross domestic product (GDP)	Undetermined
Economy
Gross domestic product (GDP, in U.S.$)	5,761 million (2004)
GDP per capita (U.S.$)	160 (2003)
GDP by economic sector
Agriculture, forestry, fishing	52 percent (2002)
Industry	24.1 percent (2002)
Services	23.9 percent (2002)
Employment
Number of workers	11,696,531 (2003)
Workforce share of economic sector
Agriculture, forestry, fishing	70 percent (1990)
Industry	11 percent (1990)
Services	19 percent (1990)
Unemployment rate	Not available
National budget (U.S.$)
Total revenue	267.1 million (2004)
Total expenditure	758 million (2004)
Monetary unit
1 afghani (AF), consisting of 100 puls
Major trade partners for exports
Pakistan, India, Finland, Germany, Belgium
Major trade partners for imports
Pakistan, South Korea, Japan, United States, Germany
Energy, Communications, and Transportation
Electricity production
Electricity from thermal sources	30.39 percent (2003 estimate)
Electricity from hydroelectric sources	69.61 percent (2003 estimate)
Electricity from nuclear sources	0 percent (2003 estimate)
Electricity from geothermal, solar, and wind sources	0 percent (2003 estimate)
Number of radios per 1,000 people	132 (1997)
Number of telephones per 1,000 people	2 (2004)
Number of televisions per 1,000 people	12 (2000 estimate)
Number of Internet hosts per 10,000 people	0 (2000)
Daily newspaper circulation per 1,000 people	6 (1996)
Number of motor vehicles per 1,000 people	2.3 (1997)
Paved road as a share of total roads	24 percent (2003)
Sources
Basic Facts and People sections
Area data are from the statistical bureaus of individual countries. Population, population growth rate, and population projections are from the United States Census Bureau, International Programs Center, International Data Base (IDB) (www.census.gov). Urban and rural population data are from the Food and Agriculture Organization (FAO) of the United Nations (UN), FAOSTAT database (www.fao.org). Largest cities population data and political divisions data are from the statistical bureaus of individual countries. Ethnic divisions and religion data are largely from the latest Central Intelligence Agency (CIA) World Factbook and from various country censuses and reports. Language data are largely from the Ethnologue, Languages of the World, Summer Institute of Linguistics International (www.sil.org).
Health and Education section
Life expectancy and infant mortality data are from the United States Census Bureau, International Programs Center, International database (IDB) (www.census.gov). Population per physician and population per hospital bed data are from the World Health Organization (WHO) (www.who.int). Education data are from the United Nations Educational, Scientific and Cultural Organization (UNESCO) database (www.unesco.org).
Government section
Government, independence, legislature, constitution, highest court, and voting qualifications data are largely from various government Web sites, the latest Europa World Yearbook, and the latest Central Intelligence Agency (CIA) World Factbook. The armed forces data is from Military Balance.
Economy section
Gross domestic product (GDP), GDP per capita, GDP by economic sectors, employment, and national budget data are from the World Bank database (www.worldbank.org). Monetary unit, agriculture, mining, manufacturing, exports, imports, and major trade partner information is from the statistical bureaus of individual countries, latest Europa World Yearbook, and various United Nations and International Monetary Fund (IMF) publications.
Energy, Communication, and Transportation section
Electricity information is from the Energy Information Administration (EIA) database (www.eia.doe.gov). Radio, telephone, television, and newspaper information is from the United Nations Educational, Scientific and Cultural Organization (UNESCO) database (www.unesco.org). Internet hosts, motor vehicles, and road data are from the World Bank database (www.worldbank.org).
Note
Figures may not total 100 percent due to rounding.

debate

Atheism

I

INTRODUCTION

Numbers of Followers of All Religions

This chart shows the percentage of the world's population that adheres to several of the major world religions. About one-third of the world’s population adheres to a form of Christianity. Latin America has the largest number of Christians, most of whom are Roman Catholics. Islam is practiced by over one-fifth of the world’s population, most of whom live in parts of Asia, particularly the Middle East.

© Microsoft Corporation. All Rights Reserved.

Atheism, the denial of or lack of belief in the existence of a god or gods. The term atheism comes from the Greek prefix a-, meaning “without,” and the Greek word theos, meaning “deity.” The denial of god’s existence is also known as strong, or positive, atheism, whereas the lack of belief in god is known as negative, or weak, atheism. Although atheism is often contrasted with agnosticism—the view that we cannot know whether a deity exists or not and should therefore suspend belief—negative atheism is in fact compatible with agnosticism.

Atheism has wide-ranging implications for the human condition. In the absence of belief in god, ethical goals must be determined by secular (nonreligious) aims and concerns, human beings must take full responsibility for their destiny, and death marks the end of a person’s existence. As of 1994 there were an estimated 240 million atheists around the world comprising slightly more than 4 percent of the world’s population, including those who profess atheism, skepticism, disbelief, or irreligion. The estimate of nonbelievers increases significantly, to about 21 percent of the world’s population, if negative atheists are included.

II

SCOPE OF ATHEISM

From ancient times, people have at times used atheism as a term of abuse for religious positions they opposed. The first Christians were called atheists because they denied the existence of the Roman deities. Over time, several misunderstandings of atheism have arisen: that atheists are immoral, that morality (see ethics) cannot be justified without belief in God, and that life has no purpose without belief in God. Yet there is no evidence that atheists are any less moral than believers. Many systems of morality have been developed that do not presuppose the existence of a supernatural being. Moreover, the purpose of human life may be based on secular goals, such as the betterment of humankind.

In Western society the term atheism has been used more narrowly to refer to the denial of theism, in particular Judeo-Christian theism, which asserts the existence of an all-powerful, all-knowing, all-good personal being. This being created the universe, takes an active interest in human concerns, and guides his creatures through divine disclosure known as revelation. Positive atheists reject this theistic God and the associated beliefs in an afterlife, a cosmic destiny, a supernatural origin of the universe, an immortal soul, the revealed nature of the Bible and the Qur'an (Koran), and a religious foundation for morality.

Theism, however, is not a characteristic of all religions. Some religions reject theism but are not entirely atheistic. Although the theistic tradition is fully developed in the Bhagavad-Gita, the sacred text of Hinduism, earlier Hindu writings known as the Upanishads teach that Brahman (ultimate reality) is impersonal. Positive atheists reject even the pantheistic aspects of Hinduism that equate God with the universe. Several other Eastern religions, including Theravada Buddhism and Jainism, are commonly believed to be atheistic, but this interpretation is not strictly correct. These religions do reject a theistic God believed to have created the universe, but they accept numerous lesser gods. At most, such religions are atheistic in the narrow sense of rejecting theism.

III

HISTORY

In the Western intellectual world, nonbelief in the existence of God is a widespread phenomenon with a long and distinguished history. Philosophers of the ancient world such as Lucretius were nonbelievers. Even in the Middle Ages (5th century to 15th century) there were currents of thought that questioned theist assumptions, including skepticism, the doctrine that true knowledge is impossible, and naturalism, the belief that only natural forces control the world. Several leading thinkers of the Enlightenment (1700-1789) were professed atheists, including Danish writer Baron Holbach and French encyclopedist Denis Diderot. Expressions of nonbelief also are found in classics of Western literature, including the writings of English poets Percy Shelley and Lord Byron; English novelist Thomas Hardy; French philosophers Voltaire and Jean-Paul Sartre; Russian author Ivan Turgenev; and American writers Mark Twain and Upton Sinclair. In the 19th century the most articulate and best-known atheists and critics of religion were German philosophers Ludwig Feuerbach, Karl Marx, Arthur Schopenhauer, and Friedrich Nietzsche. British philosopher Bertrand Russell, Austrian psychoanalyst Sigmund Freud, and Sartre are among the 20th century’s most influential atheists.

IV

REASONS FOR REJECTING GOD

Friedrich Nietzsche

Nineteenth-century German philosopher Friedrich Nietzsche was an influential critic of religious systems, especially Christianity, which he felt chained society to a herd morality. By declaring that “God is dead,” Nietzsche signified that traditional religious belief in God no longer played a central role in human experience. Nietzsche believed we would have to find secular justifications for morality to avoid nihilism--the absence of all belief.

The New York Public Library

A

Criticisms of Theism

Atheists justify their philosophical position in several different ways. Negative atheists attempt to establish their position by refuting typical theist arguments for the existence of God, such as the argument from first cause, the argument from design, the ontological argument, and the argument from religious experience (see Theism: Arguments for Theism). Other negative atheists assert that any statement about God is meaningless, because attributes such as all-knowing and all-powerful cannot be comprehended by the human mind. Positive atheists, on the other hand, defend their position by arguing that the concept of God is inconsistent. They question, for example, whether a God who is all-knowing can also be all-good and how a God who lacks bodily existence can be all-knowing.

B

The Problem of Evil

Some positive atheists have maintained that the existence of evil makes the existence of God improbable. In particular, atheists assert that theism does not provide an adequate explanation for the existence of seemingly gratuitous evil, such as the suffering of innocent children. Theists commonly defend the existence of evil by claiming that God desires that human beings have the freedom to choose between good and evil, or that the purpose of evil is to build human character, such as the ability to persevere. Positive atheists counter that justifications for evil in terms of human free will leave unexplained why, for example, children suffer because of genetic diseases or abuse from adults. Arguments that God allows pain and suffering to build human character fail, in turn, to explain why there was suffering among animals before human beings evolved and why human character could not be developed with less suffering than occurs in the world. For atheists, a better explanation for the presence of evil in the world is that God does not exist.

C

Historical Evidence

David Hume

In An Enquiry Concerning Human Understanding (first published in 1748 under a different title), Scottish philosopher David Hume offers several criticisms of religious belief, including an argument against belief in miracles. According to Hume, testimony about the occurrence of miracles should be subjected to rational standards of evidence.

THE BETTMANN ARCHIVE

Atheists have also criticized historical evidence used to support belief in the major theistic religions. For example, atheists have argued that a lack of evidence casts doubt on important doctrines of Christianity, such as the virgin birth and the resurrection of Jesus Christ. Because such events are said to represent miracles, atheists assert that extremely strong evidence is necessary to support their occurrence. According to atheists, the available evidence to support these alleged miracles—from Biblical, pagan, and Jewish sources—is weak, and therefore such claims should be rejected.

V

DIVERSITY IN ATHEISM

Atheism is primarily a reaction to, or a rejection of, religious belief, and thus does not determine other philosophical beliefs. Atheism has sometimes been associated with the philosophical ideas of materialism, which holds that only matter exists; communism, which asserts that religion impedes human progress; and rationalism, which emphasizes analytic reasoning over other sources of knowledge. However, there is no necessary connection between atheism and these positions. Some atheists have opposed communism and some have rejected materialism. Although nearly all contemporary materialists are atheists, the ancient Greek materialist Epicurus believed the gods were made of matter in the form of atoms. Rationalists such as French philosopher René Descartes have believed in God, whereas atheists such as Sartre are not considered to be rationalists. Atheism has also been associated with systems of thought that reject authority, such as anarchism, a political theory opposed to all forms of government, and existentialism, a philosophic movement that emphasizes absolute human freedom of choice; there is however no necessary connection between atheism and these positions. British analytic philosopher A. J. Ayer was an atheist who opposed existentialism, while Danish philosopher Søren Kierkegaard was an existentialist who accepted God. Marx was an atheist who rejected anarchism while Russian novelist Leo Tolstoy, a Christian, embraced anarchism. Because atheism in a strict sense is merely a negation, it does not provide a comprehensive worldview. It is therefore not possible to presume other philosophical positions to be outgrowths of atheism.

Intellectual debate over the existence of God continues to be active, especially on college campuses, in religious discussion groups, and in electronic forums on the Internet. In contemporary philosophical thought, atheism has been defended by British philosopher Antony Flew, Australian philosopher John Mackie, and American philosopher Michael Martin, among others. Leading organizations of unbelief in the United States include The American Atheists, The Committee for the Scientific Study of Religion, and The Internet Infidels.

psychology

learning environment

Memory (psychology)

I

INTRODUCTION

The Memory Artist

The paintings of Franco Magnani, a San Francisco artist, demonstrate his remarkable memory for his childhood village of Pontito, Italy. Here, one of his paintings of Pontito, top, is juxtaposed with an actual photograph of the village. Magnani left the village in 1958 in his mid-20s. Eight years later, during a serious illness, he began dreaming about Pontito in extraordinarily vivid detail. Soon the images came to him during the daytime with almost hallucinatory power. Impulsively, and working entirely from memory, he began painting and drawing different scenes of the village. Although some of his works show near-photographic accuracy, many contain distortions that serve to portray the village in an idyllic light.

Photo by S. Schwartzenberg © Exploratorium, www.exploratorium.com

Memory (psychology), processes by which people and other organisms encode, store, and retrieve information. Encoding refers to the initial perception and registration of information. Storage is the retention of encoded information over time. Retrieval refers to the processes involved in using stored information. Whenever people successfully recall a prior experience, they must have encoded, stored, and retrieved information about the experience. Conversely, memory failure—for example, forgetting an important fact—reflects a breakdown in one of these stages of memory.

Memory is critical to humans and all other living organisms. Practically all of our daily activities—talking, understanding, reading, socializing—depend on our having learned and stored information about our environments. Memory allows us to retrieve events from the distant past or from moments ago. It enables us to learn new skills and to form habits. Without the ability to access past experiences or information, we would be unable to comprehend language, recognize our friends and family members, find our way home, or even tie a shoe. Life would be a series of disconnected experiences, each one new and unfamiliar. Without any sort of memory, humans would quickly perish.

Philosophers, psychologists, writers, and other thinkers have long been fascinated by memory. Among their questions: How does the brain store memories? Why do people remember some bits of information but not others? Can people improve their memories? What is the capacity of memory? Memory also is frequently a subject of controversy because of questions about its accuracy. An eyewitness’s memory of a crime can play a crucial role in determining a suspect’s guilt or innocence. However, psychologists agree that people do not always recall events as they actually happened, and sometimes people mistakenly recall events that never happened.

Memory and learning are closely related, and the terms often describe roughly the same processes. The term learning is often used to refer to processes involved in the initial acquisition or encoding of information, whereas the term memory more often refers to later storage and retrieval of information. However, this distinction is not hard and fast. After all, information is learned only when it can be retrieved later, and retrieval cannot occur unless information was learned. Thus, psychologists often refer to the learning/memory process as a means of incorporating all facets of encoding, storage, and retrieval.

II

TYPES OF MEMORY

Simplified Model of Memory

In this information-processing model of memory, information that enters the brain is briefly recorded in sensory memory. If we focus our attention on it, the information may become part of working memory (also called short-term memory), where it can be manipulated and used. Through encoding techniques such as repetition and rehearsal, information may be transferred to long-term memory. Retrieving long-term memories makes them active again in working memory.

© Microsoft Corporation. All Rights Reserved.

Although the English language uses a single word for memory, there are actually many different kinds. Most theoretical models of memory distinguish three main systems or types: sensory memory, short-term or working memory, and long-term memory. Within each of these categories are further divisions.

A

Sensory Memory

Sensory memory refers to the initial, momentary recording of information in our sensory systems. When sensations strike our eyes, they linger briefly in the visual system. This kind of sensory memory is called iconic memory and refers to the usually brief visual persistence of information as it is being interpreted by the visual system. Echoic memory is the name applied to the same phenomenon in the auditory domain: the brief mental echo that persists after information has been heard. Similar systems are assumed to exist for other sensory systems (touch, taste, and smell), although researchers have studied these senses less thoroughly.

American psychologist George Sperling demonstrated the existence of sensory memory in an experiment in 1960. Sperling asked subjects in the experiment to look at a blank screen. Then he flashed an array of 12 letters on the screen for one-twentieth of a second, arranged in the following pattern:

Subjects were then asked to recall as many letters from the image as they could. Most could only recall four or five letters accurately. Subjects knew they had seen more letters, but they were unable to name them. Sperling hypothesized that the entire letter-array image registered briefly in sensory memory, but the image faded too quickly for subjects to “see” all the letters. To test this idea, he conducted another experiment in which he sounded a tone immediately after flashing the image on the screen. A high tone directed subjects to report the letters in the top row, a medium tone cued subjects to report the middle row, and a low tone directed subjects to report letters in the bottom row. Sperling found that subjects could accurately recall the letters in each row most of the time, no matter which row the tone specified. Thus, all of the letters were momentarily available in sensory memory.

Sensory memory systems typically function outside of awareness and store information for only a very short time. Iconic memory seems to last less than a second. Echoic memory probably lasts a bit longer; estimates range up to three or four seconds. Usually sensory information coming in next replaces the old information. For example, when we move our eyes, new visual input masks or erases the first image. The information in sensory memory vanishes unless it captures our attention and enters working memory.

B

Short-Term or Working Memory

Serial Position Effect

In a 1966 experiment, subjects were shown a series of 15 words, then tested for their recall of the words immediately or after 30 seconds. When tested immediately, people remembered items at the beginning and end of the series better than those in the middle, a phenomenon called the serial position effect. Memory for words at the end of the list faded when the test was delayed 30 seconds.

© Microsoft Corporation. All Rights Reserved.

Psychologists originally used the term short-term memory to refer to the ability to hold information in mind over a brief period of time. As conceptions of short-term memory expanded to include more than just the brief storage of information, psychologists created new terminology. The term working memory is now commonly used to refer to a broader system that both stores information briefly and allows manipulation and use of the stored information.

We can keep information circulating in working memory by rehearsing it. For example, suppose you look up a telephone number in a directory. You can hold the number in memory almost indefinitely by saying it over and over to yourself. But if something distracts you for a moment, you may quickly lose it and have to look it up again. Forgetting can occur rapidly from working memory. For more information on the duration of working memory, see the Rate of Forgetting section of this article.

Psychologists often study working memory storage by examining how well people remember a list of items. In a typical experiment, people are presented with a series of words, one every few seconds. Then they are instructed to recall as many of the words as they can, in any order. Most people remember the words at the beginning and end of the series better than those in the middle. This phenomenon is called the serial position effect because the chance of recalling an item is related to its position in the series. The results from one such experiment are shown in the accompanying chart entitled “Serial Position Effect.” In this experiment, recall was tested either immediately after presentation of the list items or after 30 seconds. Subjects in both conditions demonstrated what is known as the primacy effect, which is better recall of the first few list items. Psychologists believe this effect occurs because people tend to process the first few items more than later items. Subjects in the immediate-recall condition also showed the recency effect, or better recall of the last items on the list. The recency effect occurs because people can store recently presented information temporarily in working memory. When the recall test is delayed for 30 seconds, however, the information in working memory fades, and the recency effect disappears.

Working memory has a basic limitation: It can hold only a limited amount of information at one time. Early research on short-term storage of information focused on memory span—how many items people can correctly recall in order. Researchers would show people increasingly long sequences of digits or letters and then ask them to recall as many of the items as they could. In 1956 American psychologist George Miller reviewed many experiments on memory span and concluded that people could hold an average of seven items in short-term memory. He referred to this limit as “the magical number seven, plus or minus two” because the results of the studies were so consistent. More recent studies have attempted to separate true storage capacity from processing capacity by using tests more complex than memory span. These studies have estimated a somewhat lower short-term storage capacity than did the earlier experiments. People can overcome such storage limitations by grouping information into chunks, or meaningful units. This topic is discussed in the Encoding and Recoding section of this article.

Working memory is critical for mental work, or thinking. Suppose you are trying to solve the arithmetic problem 64 × 9 in your head. You probably would need to perform some intermediate calculations in your head before arriving at the final answer. The ability to carry out these kinds of calculations depends on working memory capacity, which varies individually. Studies have also shown that working memory changes with age. As children grow older, their working memory capacity increases. Working memory declines in old age and in some types of brain diseases, such as Alzheimer’s disease.

Working memory capacity is correlated with intelligence (as measured by intelligence tests). This correlation has led some psychologists to argue that working memory abilities are essentially those that underlie general intelligence. The more capacity people have to hold information in mind while they think, the more intelligent they are. In addition, research suggests that there are different types of working memory. For example, the ability to hold visual images in mind seems independent from the ability to retain verbal information.

C

Long-Term Memory

The term long-term memory is somewhat of a catch-all phrase because it can refer to facts learned a few minutes ago, personal memories many decades old, or skills learned with practice. Generally, however, long-term memory describes a system in the brain that can store vast amounts of information on a relatively enduring basis. When you play soccer, remember what you had for lunch yesterday, recall your first birthday party, play a trivia game, or sing along to a favorite song, you draw on information and skills stored in long-term memory.

Psychologists have different theories about how information enters long-term memory. The traditional view is that that information enters short-term memory and, depending on how it is processed, may then transfer to long-term memory. However, another view is that short-term memory and long-term memory are arranged in a parallel rather than sequential fashion. That is, information may be registered simultaneously in the two systems.

There seems to be no finite capacity to long-term memory. People can learn and retain new facts and skills throughout their lives. Although older adults may show a decline in certain capacities—for example, recalling recent events—they can still profit from experience even in old age. For example, vocabulary increases over the entire life span. The brain remains plastic and capable of new learning throughout one’s lifetime, at least under normal conditions. Certain neurological diseases, such as Alzheimer’s disease, can greatly diminish the capacity for new learning.

Psychologists once thought of long-term memory as a single system. Today, most researchers distinguish three long-term memory systems: episodic memory, semantic memory, and procedural memory.

C1

Episodic Memory

Episodic memory refers to memories of specific episodes in one’s life and is what most people think of as memory. Episodic memories are connected with a specific time and place. If you were asked to recount everything you did yesterday, you would rely on episodic memory to recall the events. Similarly, you would draw on episodic memory to describe a family vacation, the way you felt when you won an award, or the circumstances of a childhood accident. Episodic memory contains the personal, autobiographical details of our lives.

C2

Semantic Memory

Pyramid of Khafre at Giza

Knowing that Egypt has pyramids is a form of semantic memory, which refers to our general knowlege of the world.

Giraudon/Bridgeman Art Library, London/New York

Semantic memory refers to our general knowledge of the world and all of the facts we know. Semantic memory allows a person to know that the chemical symbol for salt is NaCl, that dogs have four legs, that Thomas Jefferson was president of the United States, that 3 × 3 equals 9, and thousands of other facts. Semantic memories are not tied to the particular time and place of learning. For example, in order to remember that Thomas Jefferson was president, people do not have to recall the time and place that they first learned this fact. The knowledge transcends the original context in which it was learned. In this respect, semantic memory differs from episodic memory, which is closely related to time and place. Semantic memory also seems to have a different neural basis than episodic memory. Brain-damaged patients who have great difficulties remembering their own recent personal experiences often can access their permanent knowledge quite readily. Thus, episodic memory and semantic memory seem to represent independent capacities.

C3

Procedural Memory

Mountain Biking

These two cyclists riding mountain bikes are drawing on procedural memory, a form of long-term memory that deals with learned skills and does not require conscious effort to recall.

Dave Nagel/Liaison Agency

Procedural memory refers to the skills that humans possess. Tying shoelaces, riding a bicycle, swimming, and hitting a baseball are examples of procedural memory. Procedural memory is often contrasted with episodic and semantic memory. Episodic and semantic memory are both classified as types of declarative memory because people can consciously recall facts, events, and experiences and then verbally declare or describe their recollections. In contrast, nondeclarative, or procedural, memory is expressed through performance and typically does not require a conscious effort to recall.

Practice and Speed in Cigar-Making

Workers in a cigar factory continued to improve their speed of production even after making millions of cigars. Only after two years did their performance begin to level off, demonstrating that skills can improve over long periods of time.

© Microsoft Corporation. All Rights Reserved.

Could you learn how to tie your shoelaces or to swim through purely declarative means—say, by reading or listening to descriptions of how to do it? If it would be possible at all, the process would be slow, difficult, and unnatural. People best gain procedural knowledge by practicing the procedures directly, not via instructions given in words. Verbal coaching in sports is partly a case of trying to impart procedural knowledge through declarative means, although coaching by example (and videotape) may work better. Still, in most cases there is no substitution for practice. Procedural learning may take considerable effort, and improvements can occur over a long period of time. The accompanying chart, entitled “Practice and Speed in Cigar-Making,” shows the effect of practice on Cuban factory workers making cigars. The performance of the workers continued to improve even after they had produced more than 100,000 cigars.

C4

Interaction of Long-Term Memory Systems

Although long-term episodic, semantic, and procedural memory all represent independent systems, it would usually be wrong to think of a particular task as relying exclusively on one type. The examples used above (remembering yesterday’s events, knowing that Thomas Jefferson was president, or tying shoes) represent relatively pure cases. However, most human activities rely on the interaction of long-term memory systems. Consider the expression of social skills or, more specifically, table manners. If you know to set the dinner table with the fork to the left of each plate, is this an example of procedural memory, semantic memory, or even episodic memory from having witnessed a past example? Probably the answer is some blend of all three. In addition, procedural memory does not apply only to physical skills, as in the previous examples. Complex cognitive behavior, such as reading or remembering, also has a procedural component—the mental procedures we execute to perform these activities. Thus, the separation of procedural and declarative memory from one another is not clear-cut in all cases.

III

ENCODING AND RECODING

Chunking

Chunking, or recoding, is grouping separate bits of information into meaningful units (chunks) that are easier to remember.

© Microsoft Corporation. All Rights Reserved.

Encoding is the process of perceiving information and bringing it into the memory system. Encoding is not simply copying information directly from the outside world into the brain. Rather, the process is properly conceived as recoding, or converting information from one form to another. The human visual system provides an example of how information can change forms. Light from the outside world enters the eye in the form of waves of electromagnetic radiation. The retina of the eye transduces (converts) this radiation to bioelectrical signals that the brain interprets as visual images. Similarly, when people encode information into memory, they convert it from one form to another to help them remember it later. For example, a simple digit, such as 7, can be recoded in many ways: as the word seven, the roman numeral VII, a prime number, the square root of 49, and so on. Recoding is routine in memory. Each of us has a unique background and set of experiences that help or hinder us in learning new information. An ornithologist could learn a list of obscure bird names much more easily than most of us due to his or her prior knowledge about birds, which would permit efficient recoding.

Recoding is often the key to efficient remembering. To understand the concept of recoding, first try to remember the following series of numbers by reading it once out loud, closing your eyes, and trying to recall the items in their correct order: one, four, nine, one, six, two, five, three, six, four, nine, six, four, eight, one. Test yourself now. If you are like most people, you might have recalled around 7 of the 15 digits in their correct order. However, a simple recoding strategy would have helped you to recall them effortlessly. Write the numbers out in digits and you may notice that they represent the squares of the numbers of 1 to 9: 1, 4, 9, 16, 25, 36, 49, 64, 81. That is, 1 squared is 1, 2 squared is 4, 3 squared is 9, 4 squared is 16, and so on. Recoding the series of numbers as a meaningful rule—the squares of the numbers 1 to 9—would have permitted you to remember all 15 digits. Although this example is contrived, the principle that underlies it is universally valid: How well a person remembers information depends on how the information is recoded. Recoding is sometimes called chunking, because separate bits of information can be grouped into meaningful units, or chunks. For example, the five letters e, t, s, e, and l can be rearranged into sleet and one word remembered instead of five individual units.

Can You Recognize a Penny?

Learn about a principle of memory by guessing which of the pennies in the illustration is real.

© Microsoft Corporation. All Rights Reserved.

Psychologists have studied many different recoding strategies. One common strategy that people often use to remember items of information is to rehearse them, or to repeat them mentally. However, simply repeating information over and over again rarely aids long-term retention—although it works perfectly well to hold information, such as a phone number, in working memory. A more effective way to remember information is through effortful or elaborative processing, which involves thinking about information in a meaningful way and associating it with existing information in long-term memory.

One effective form of effortful processing is turning information into mental imagery. For example, one experiment compared two groups of people that were given different instructions on how to encode a list of words into memory. Some people were told to repeat the words over and over, and some were told to form mental pictures of the words. For words referring to concrete objects, such as truck and volleyball, forming mental images of each object led to better later recall than did rote rehearsal.

Depth of Processing and Memory

People remember information better when they process it in a meaningful rather than superficial way. In a 1975 experiment, subjects were shown a series of words and asked questions about each one. The questions induced subjects to pay attention to the word’s physical appearance, the way it sounded, or its meaning. The more deeply they processed the words, the better they recognized them on a later test.

© Microsoft Corporation. All Rights Reserved.

Thinking about the meaning of information is also a good technique for most memory tasks. Studies have found that the more deeply we process information, the more likely we are to recall it later. In 1975 Canadian psychologists Fergus Craik and Endel Tulving conducted a set of experiments that demonstrated this effect. The experimenters asked subjects to answer questions about a series of words, such as bear, which were flashed one at a time. For each word, subjects were asked one of three types of questions, each requiring a different level of processing or analysis. Sometimes subjects were asked about the word’s visual appearance: “Is the word in upper case letters?” For other words, subjects were asked to focus on the sound of the word: “Does it rhyme with chair?” The third type of question required people to think about the meaning of the word: “Is it an animal?” When subjects were later given a recognition test for the words they had seen, they were poor at recognizing words they had encoded superficially by visual appearance or sound. They were far better at recognizing words they had encoded for meaning. (See the accompanying chart entitled “Depth of Processing and Memory.”)

Although some information requires deliberate, effortful processing to store in long-term memory, a vast amount of information is encoded automatically, without effort or awareness. Every day each of us encodes and stores thousands of events and facts, most of which we will never need to recall. For example, people do not have to make a conscious effort to remember the face of a person they meet for the first time. They can easily recognize the person’s face in future encounters. Studies have shown that people also encode information about spatial locations, time, and the frequency of events without intending to. For instance, people can recognize how many times a certain word was presented in a long series of words with relative accuracy.

People have developed many elaborate and imaginative recoding strategies, known as mnemonic devices, to aid them in remembering information. For descriptions of mnemonic devices, see the Ways to Improve Memory section of this article.

IV

MEMORY RETRIEVAL

Encoding and storage are necessary to acquire and retain information. But the crucial process in remembering is retrieval, without which we could not access our memories. Unless we retrieve an experience, we do not really remember it. In the broadest sense, retrieval refers to the use of stored information.

For many years, psychologists considered memory retrieval to be the deliberate recollection of facts or past experiences. However, in the early 1980s psychologists began to realize that people can be influenced by past experiences without any awareness that they are remembering. For example, a series of experiments showed that brain-damaged amnesic patients—who lose certain types of memory function—were influenced by previously viewed information even though they had no conscious memory of having seen the information before. Based on these and other findings, psychologists now distinguish two main classes of retrieval processes: explicit memory and implicit memory.

A

Explicit Memory

Explicit memory refers to the deliberate, conscious recollection of facts and past experiences. If someone asked you to recall everything you did yesterday, this task would require explicit memory processes. There are two basic types of explicit memory tests: recall tests and recognition tests.

In recall tests, people are asked to retrieve memories without the benefit of any hints or cues. A request to remember everything that happened to you yesterday or to recollect all the words in a list you just heard would be an example of a recall test. Suppose you were briefly shown a series of words: cow, prize, road, gem, hobby, string, weather. A recall test would require you to write down or say as many of the words as you could. If you were instructed to recall the words in any order, the test would be one of free recall. If you were directed to recall the words in the order they were presented, the test would one of serial recall or ordered recall. Another type of test is cued recall, in which people are given cues or prompts designed to aid recall. Using the above list as an example, a cued recall test might ask, “What word on the list was related to car?” In school, tests that require an essay or fill-in-the-blank response are examples of recall tests. All recall tests require people to explicitly retrieve events from memory.

Recognition tests require people to examine a list of items and identify those they have seen before, or to determine whether they have seen a single item before. Multiple-choice and true-false exams are types of recognition tests. For example, a recognition test on the list of words above might ask, “Which of the following words appeared on the list? (a) plant (b) driver (c) string (d) radio.” People can often recognize items that they cannot recall. You have probably had the experience of not being able to answer a question but then recognizing an answer as correct when someone else supplies it. Likewise, adults shown yearbook pictures of their high-school classmates often have difficulty recalling the classmates’ names, but they can easily pick the classmates’ names out of a list.

In some cases, recall can be better than recognition. For example, if asked, “Do you know a famous person named Cooper?” you might answer “no.” However, given the cue “James Fenimore,” you might recall American writer James Fenimore Cooper, even though you did not recognize the surname by itself.

B

Implicit Memory

Word Memory in Amnesia

In a 1984 experiment, researchers demonstrated that patients with amnesia can retain information even though they cannot recall it consciously. Both amnesic and normal subjects studied a list of words and then wrote down as many of the words as they could remember. Amnesic patients remembered very few words. But on a test that required them to complete word fragments (such as def___), they completed the fragments with previously studied words far more often than would be expected by guessing, performing about the same as normal subjects.

© Microsoft Corporation. All Rights Reserved.

Implicit memory refers to using stored information without trying to retrieve it. People often retain and use prior experiences without realizing it. For example, suppose that the word serendipity is not part of your normal working vocabulary, and one day you hear the word used in a conversation. A day later you find yourself using the word in conversation and wonder why. The earlier exposure to the word primed you to retrieve it automatically in the right situation without intending to do so.

Another example of implicit memory in everyday life is unintentional plagiarism. That is, people can copy the ideas of others without being aware they are doing so. The most famous case involved British singer-songwriter George Harrison, formerly of the Beatles. Harrison was sued because his 1970 hit song “My Sweet Lord” sounded strikingly similar to “He’s So Fine,” a 1963 hit by The Chiffons. Harrison denied that he had intentionally copied the earlier song but admitted that he had heard it before writing “My Sweet Lord.” In 1976 a judge ruled against Harrison, concluding that the singer had been unconsciously influenced by his memory.

Implicit and Explicit Memory

Implicit memory tests seem to tap a very different set of memory processes than do explicit memory tests. In a 1992 experiment, subjects were shown a series of words and asked to pay attention either to the words’ physical appearance (letter shapes) or to their meaning. In a later task, the subjects were asked to complete word stems (such as ele_____). Some subjects believed the task was unrelated to the previously studied words and were told to complete the fragment with the first word that came to mind. Others knew that the fragments were clues from the previously studied words. Surprisingly, whether people paid attention to the words' appearance or meaning—a variable that greatly influenced people's explicit memory test performance—had no effect on implicit memory test performance.

© Microsoft Corporation. All Rights Reserved.

Psychologists use the term priming to describe the relatively automatic change in performance resulting from prior exposure to information. Priming occurs even when people do not consciously remember being exposed to the information. One way to look for evidence of implicit memory, therefore, is to measure priming effects. In typical implicit memory experiments, subjects study a long list of words, such as assassin and boyhood. Later, subjects are presented with a series of word fragments (such as a_ _a_ _in and b_ _ho_d) or word “stems” (as______ or bo_____) and are instructed to complete the fragment or stem with the first word that comes to mind. The subjects are not explicitly asked to recall the list words. Nevertheless, the previous presentation of assassin and boyhood primes subjects to complete the fragments with these words more often than would be expected by guessing. This priming effect occurs even if the subjects do not remember studying the words before—strong evidence of implicit memory. The hallmark of all implicit memory tests is that people are not required to remember; rather, they are given a task, and past experience is expressed on the test relatively automatically.

Remarkably, even amnesic individuals show implicit memory. In one experiment, amnesic patients and normal subjects studied lists of words and then were given both an explicit memory test (free recall) and an implicit memory test (word-stem completion). Relative to control subjects, the amnesic patients failed miserably at the free-recall test. Due to their memory disorder, they could consciously remember very few of the list words. On the implicit test, however, the amnesic patients performed as well or better than the normal subjects (see the accompanying chart entitled “Word Memory in Amnesia”). Even though the amnesic patients could not consciously access the desired information, they expressed prior learning in the form of priming on the implicit memory test. They retained the information without knowing it.

Studies have found that a person’s performance on implicit memory tests can be relatively independent of his or her performance on explicit tests. Some factors that have large effects on explicit memory test performance have no effect—or even the opposite effect—on implicit memory test performance. For example, whether people pay attention to the appearance, the sound, or the meaning of words has a huge effect on how well they can explicitly recall the words later. But this variable has practically no effect on their implicit memory test performance (see the accompanying chart entitled “Explicit and Implicit Memory”). Implicit tests seem to tap a different form of memory.

C

Retrieval Cues

State-Dependent Memory

In a 1977 experiment, volunteers drank an alcoholic or nonalcoholic beverage before studying a list of words. A day later, they tried to recall as many words as they could while either intoxicated or sober. Subjects who were intoxicated during both the study and test phases remembered more than those intoxicated only during the study phase, demonstrating the phenomenon of state-dependent memory.

© Microsoft Corporation. All Rights Reserved.

One fascinating feature of remembering is how a cue from the external world can cause us to suddenly remember something from years ago. For example, returning to where you once lived or went to school may bring back memories of events experienced long ago. Sights, sounds, and smells can all trigger recall of long dormant events. These experiences point to the critical nature of retrieval in remembering.

A retrieval cue is any stimulus that helps us recall information in long-term memory. The fact that retrieval cues can provoke powerful recollections has led some researchers to speculate that perhaps all memories are permanent. That is, perhaps nearly all experiences are recorded in memory for a lifetime, and all forgetting is due not to the actual loss of memories but to our inability to retrieve them. This idea is an interesting one, but most memory researchers believe it is probably wrong.

Two general principles govern the effectiveness of retrieval cues. One is called the encoding specificity principle. According to this principle, stimuli may act as retrieval cues for an experience if they were encoded with the experience. Pictures, words, sounds, or smells will cause us to remember an experience to the extent that they are similar to the features of the experience that we encoded into memory. For example, the smell of cotton candy may trigger your memory of a specific amusement park because you smelled cotton candy there.

Distinctiveness is another principle that determines the effectiveness of retrieval cues. Suppose a group of people is instructed to study a list of 100 items. Ninety-nine are words, but one item in the middle of the list is a picture of an elephant. If people were given the retrieval cue “Which item was the picture?” almost everyone would remember the elephant. However, suppose another group of people was given a different 100-item list in which the elephant picture appeared in the same position, but all the other items were also pictures of other objects and animals. Now the retrieval cue would not enable people to recall the picture of the elephant because the cue is no longer distinctive. Distinctive cues specify one or a few items of information.

Overt cues such as sights and sounds can clearly induce remembering. But evidence indicates that more subtle cues, such as moods and physiological states, can also influence our ability to recall events. State-dependent memory refers to the phenomenon in which people can retrieve information better if they are in the same physiological state as when they learned the information. The initial observations that aroused interest in state-dependent memory came from therapists working with alcoholic patients. When sober, patients often could not remember some act they performed when intoxicated. For example, they might put away a paycheck while intoxicated and then forget where they put it. This memory failure is not surprising, because alcohol and other depressant drugs (such as marijuana, sedatives, and even antihistamines) are known to impair learning and memory. However, in the case of the alcoholics, if they got drunk again after a period of abstinence, they sometimes recovered the memory of where the paycheck was. This observation suggested that perhaps drug-induced states function as a retrieval cue.

A number of studies have confirmed this hypothesis. In one typical experiment, volunteers drank an alcoholic or nonalcoholic beverage before studying a list of words. A day later, the same subjects were asked to recall as many of the words as they could, either in the same state as they were in during the learning phase (intoxicated or sober) or in a different state. Not surprisingly, individuals intoxicated during learning but sober during the test did worse at recall than those sober during both phases. In addition, people who studied material sober and then were tested while intoxicated did worse than those sober for both phases. The most interesting finding, however, was that people intoxicated during both the learning and test phase did much better at recall than those who were intoxicated only during learning, showing the effect of state-dependent memory (see the chart entitled “State-Dependent Memory”). When people are in the same state during study and testing, their recall is better than those tested in a different state. However, one should not conclude that alcohol improves memory. As noted, alcohol and other depressant drugs usually impair memory and most other cognitive processes. Those who had alcohol during both phases remembered less than those who were sober during both phases.

Psychologists have also studied the topic of mood-dependent memory. If people are in a sad mood when exposed to information, will they remember it better later if they are in a sad mood when they try to retrieve it? Although experiments testing this idea have produced mixed results, most find evidence for mood-dependent memory. Recall tests are usually more sensitive to mood- and state-dependent effects than are recognition or implicit memory tests. Recognition tests may provide powerful retrieval cues that overshadow the effects of more subtle state and mood cues.

Mood- and state-dependent memory effects are further examples of the encoding specificity principle. If mood or drug state is encoded as part of the learning experience, then providing this cue during retrieval enhances performance.

D

Curious Phenomena of Retrieval

Psychologists have explored several puzzling phenomena of retrieval that nearly everyone has experienced. These include déjà vu, jamais vu, flashbulb memories, and the tip-of-the-tongue state.

D1

Déjà Vu and Jamais Vu

The sense of déjà vu (French for “seen before”) is the strange sensation of having been somewhere before, or experienced your current situation before, even though you know you have not. One possible explanation of déjà vu is that aspects of the current situation act as retrieval cues that unconsciously evoke an earlier experience, resulting in an eerie sense of familiarity. Another puzzling phenomenon is the sense of jamais vu (French for “never seen”). This feeling arises when people feel they are experiencing something for the first time, even though they know they must have experienced it before. The encoding specificity principle may partly explain jamais vu; despite the overt similarity of the current and past situations, the cues of the current situation do not match the encoded features of the earlier situation.

D2

Flashbulb Memories

Challenger Shuttle Disaster

Many people remember where they were when they heard about the explosion of the United States space shuttle Challenger on January 28, 1986. Vivid memories associated with especially dramatic or emotional events are known as flashbulb memories.

NASA/Photo Researchers, Inc./Courtesy of CBS News Archives and the Gordon Skene Sound Collection. All rights reserved.

A flashbulb memory is an unusually vivid memory of an especially emotional or dramatic past event. For example, the death of Princess Diana in 1997 created a flashbulb memory for many people. People remember where they were when they heard the news, whom they heard it from, and other seemingly fine details of the event and how they learned of it. Examples of other public events for which many people have flashbulb memories are the assassination of U.S. President John F. Kennedy in 1963, the explosion of the space shuttle Challenger in 1986, and the bombing of the Oklahoma City federal building in 1995. Flashbulb memories may also be associated with vivid emotional experiences in one’s own life: the death of a family member or close friend, the birth of a baby, being in a car accident, and so on.

Are flashbulb memories as accurate as they seem? In one study, people were asked the day after the Challenger explosion to report how they learned about the news. Two years later the same people were asked the same question. One-third of the people gave answers different from the ones they originally reported. For example, some people initially reported hearing about the event from a friend, but then two years later claimed to have gotten the news from television. Therefore, flashbulb memories are not faultless, as is often supposed.

Flashbulb memories may seem particularly vivid for a variety of reasons. First, the events are usually quite distinctive and hence memorable. In addition, many studies show that events causing strong emotion (either positive or negative) are usually well remembered. Finally, people often think about and discuss striking events with others, and this periodic rehearsal may help to increase retention of the memory.

D3

Tip-of-the-Tongue State

Another curious phenomenon is the tip-of-the-tongue state. This term refers to the situation in which a person tries to retrieve a relatively familiar word, name, or fact, but cannot quite do so. Although the missing item seems almost within grasp, its retrieval eludes the person for some time. The feeling has been described as like being on the brink of a sneeze. Most people regard the tip-of-the-tongue state as mildly unpleasant and its eventual resolution, if and when it comes, as a relief. Studies have shown that older adults are more prone to the tip-of-the-tongue phenomenon than are younger adults, although people of all ages report the experience.

Often when a person cannot retrieve the correct bit of information, some other wrong item intrudes into one’s thoughts. For example, in trying to remember the name of a short, slobbering breed of dog with long ears and a sad face, a person might repeatedly retrieve beagle but know that it is not the right answer. Eventually the person might recover the sought-after name, basset hound.

One theory of the tip-of-the tongue state is that the intruding item essentially clogs the retrieval mechanism and prevents retrieval of the correct item. That is, the person cannot think of basset hound because beagle gets in the way and blocks retrieval of the correct name. Another idea is that the phenomenon occurs when a person has only partial information that is simply insufficient to retrieve the correct item, so the failure is one of activation of the target item (basset hound in this example). Both the partial activation theory and the blocking theory could be partly correct in explaining the tip-of-the-tongue phenomenon.

V

ACCURACY AND DISTORTION OF MEMORY

One of the most controversial issues in the study of memory is the accuracy of recollections, especially over long periods of time. We would like to believe that our cherished memories of childhood and other periods in our life are faithful renditions of the past. However, several case studies and many experiments show that memories—even when held with confidence—can be quite erroneous.

The Swiss psychologist Jean Piaget reported a striking case from his own past. He had a firm memory from early childhood of his nurse fending off an attempted kidnapping, with himself as the potential victim. He remembered his nanny pushing him in his carriage when a man came up and tried to kidnap him. He had a detailed memory of the man, of the location of the event, of scratches that his nanny received when she fended off the villain, and finally, of a police officer coming to the rescue. However, when Piaget was 15 years old, his nanny decided to confess her past sins. One of these was that she had made up the entire kidnapping story to attract sympathy and scratched herself to make it seem real. The events Piaget so vividly remembered from his childhood had never actually occurred! Piaget concluded that the false memory was probably implanted by the nanny’s frequent retelling of the original story over the years. Eventually, the scene became rooted in Piaget’s memory as an actual event.

A

Memory Reconstruction

Psychologists generally accept the idea that long-term memories are reconstructive. That is, rather than containing an exact and detailed record of our past, like a video recording, our memories are instead more generic. As a better analogy, consider paleontologists who must reconstruct a dinosaur from bits and pieces of actual bones. They begin with a general idea or scheme of what the dinosaur looked like and then fit the bits and pieces into the overall framework. Likewise, in remembering, we begin with general themes about past events and later weave in bits and pieces of detail to develop a coherent story. Whether the narrative that we weave today can faithfully capture the distant past is a matter of dispute. In many cases psychologists have discovered that recollections can deviate greatly from the way the events actually occurred, just as in the anecdote about Piaget.

Sir Frederic Bartlett, a British psychologist, argued for the reconstructive nature of memory in the 1930s. He introduced the term schema and its plural form schemata to refer to the general themes that we retain of experience. For example, if you wanted to remember a new fairy tale, you would try to integrate information from the new tale into your general schema for what a fairy tale is. Many researchers have showed that schemata can distort the memories that people form of events. That is, people will sometimes remove or omit details of an experience from memory if they do not fit well with the schema. Similarly, people may confidently remember details that did not actually occur because they are consistent with the schema.

Another way our cognitive system introduces error is by means of inference. Whenever humans encode information, they tend to make inferences and assumptions that go beyond the literal information given. For example, one study showed that if people read a sentence such as “The karate champion hit the cinder block,” they would often remember the sentence as “The karate champion broke the cinder block.” The remembered version of the events is implied by the original sentence but is not literally stated there (the champion may have hit the block and not broken it). Many memory distortions arise from these errors of encoding, in which the information encoded into memory is not literally what was perceived but is some extension of it.

B

Eyewitness Testimony

McMartin Preschool Case

In 1984 prosecutors indicted seven teachers at the McMartin Preschool in Manhattan Beach, California, on charges they had sexually abused dozens of children. Charges were dropped against five of the teachers, but the subsequent trial of Peggy McMartin Buckey, left, and her son Ray Buckey, far right, was one of the longest and costliest trials in American history. The case relied heavily on pretrial interviews of the preschool children conducted by therapists. In these interviews, the children accused the Buckeys of rape, sodomy, satanic rituals, trips to cemeteries to dig up bodies, and other bizarre acts. Were the children’s memories reliable? Psychologists for the defense argued that the therapists essentially taught the children scripted stories of abuse using highly suggestive and even coercive methods of questioning. In 1990 a jury acquitted the Buckeys. Research has shown that strong suggestions from a therapist can help implant false memories in people and that children can be more vulnerable to these suggestions than adults.

Corbis

The question of memory distortion has particular importance in the courtroom. Each year thousands of people are charged with crimes solely on the basis of eyewitness testimony, and in many trials an eyewitness’s testimony is the main evidence by which juries decide a suspect’s guilt or innocence. Are eyewitnesses’ memories accurate? Although eyewitness testimony is often correct, psychologists agree that witnesses are not always accurate in their recollections of events. We have already described how people often remember events in a way that fits with their expectations or schema for a situation. In addition, evidence shows that memories may be distorted after an event has occurred. After experiencing or seeing a crime, an eyewitness is exposed to a great deal of further information related to the crime. The witness may be interrogated by police, by attorneys, and by friends. He or she may also read information related to the case. Such information, coming weeks or months after the crime, can cause witnesses to reconstruct their memory of the crime and change what they say on the witness stand.

American psychologist Elizabeth Loftus has conducted many experiments that demonstrate how eyewitnesses can reconstruct their memories based on misleading information. In one study, subjects watched a videotape of an automobile accident involving two cars. Later they were given a questionnaire about the incident, one item of which asked, “About how fast were the cars going when they hit each other?” For some groups of subjects, however, the verb hit was replaced by smashed, collided, bumped, or contacted. Although all subjects viewed the same videotape, their speed estimates differed considerably as a function of how the question was asked. The average speed estimate was 32 mph when the verb was contacted, 34 mph when it was hit, 38 mph when it was bumped, 39 mph when it was collided, and 41 mph when it was smashed. In a follow-up study, subjects were asked a week later whether there was any broken glass at the accident scene. In reality, the film showed no broken glass. Those questioned with the word smashed were more than twice as likely to “remember” broken glass than those asked the question with hit. The information coming in after the original event was integrated with that event, causing it to be remembered in a different way.

Misinformation Effect

Research shows that people tend to distort their memories of an event when later exposed to misleading information about it, a phenomenon known as the misinformation effect. In one experiment, American psychologist Elizabeth Loftus and her colleagues showed subjects a series of slides depicting an automobile accident with a pedestrian at an intersection. As part of the sequence, half of the subjects saw a car stopped at a yield sign, top, and the other half saw the car stopped at a stop sign, bottom. After the slide show, some subjects in both groups were asked misleading questions about what they had seen. For example, half of the subjects who had seen the stop sign were asked, “Did another car pass the red Datsun while it was stopped at the yield sign?” Later, subjects were asked to choose which of two slides they had seen earlier: the one with a stop sign or the one with a yield sign. People that had received misleading questions chose the correct slide only 41 percent of the time, whereas those not given misleading information were correct 75 percent of the time.

Courtesy of Elizabeth Loftus

This study, and dozens of others like it, shows the power of leading questions: The form in which the question is asked helps determine its answer. Our memories are not encapsulated little packets lying in the brain undisturbed until they are needed for retrieval. Rather, people are prone to the misinformation effect—the tendency to distort one’s memory of an event when later exposed to misleading information about it. Eyewitnesses’ testimony can be tainted and altered by information they hear or see after the critical event in question. Therefore, in court cases one must carefully consider whether the testimony of an eyewitness could possibly have been altered through misleading suggestions provided between the time of the crime and the court case.

The problem of determining whether memories are accurate is even more difficult when children are the witnesses. Research shows that in some situations children are more prone to memory distortions than are young adults. In addition, older adults (over 70 years of age) often show a greater tendency to memory distortion than do younger adults.

Even though psychologists have shown that memories can be distorted and that people can remember things that never occurred, our memories are certainly not totally faulty. Usually memory does capture the gist of events that have occurred to us, even if details may be readily distorted.

C

Recovered Memories

Can people recover memories of childhood experiences in adulthood, ones that they had never thought about since childhood? Can a powerful retrieval cue suddenly trigger a memory for some long-lost event? Although these questions are interesting, scientific evidence does not yet exist to answer them convincingly. Of course, people often do remember childhood experiences quite clearly, but these memories are usually of significant events that have been repeatedly retrieved over the years. The questions above, on the other hand, pertain to unique events that have not been repeatedly retrieved. Can people remember something when they are 40 years old that happened to them when they were 10 years old—something that they have never thought about during the intervening 30 years?

Such questions take on renewed relevance in what is called the recovered memory controversy. Although the term recovered memory could be applied to retrieval of any memory from the distant past, it is normally used to refer to a particular type of case in contemporary psychology: the long-delayed recovery of sexual abuse in childhood. In a typical case, a person—often, but not always, undergoing psychotherapy—claims to recover a memory of some horrific childhood event. The prototypical case involves an adult woman recovering a memory of being sexually abused by a male figure from her childhood, such as being raped by a father, uncle, or teacher. Sometimes the memory is recovered suddenly, but often the recovery is gradual, occurring over days and weeks. After recovering the memory, the person may confront and accuse the individual deemed responsible, or even take the person to court. The accused person almost always vehemently denies the allegation and claims the events never took place. Whom is to be believed?

A huge debate swirls over the accuracy of recovered memories. Proponents of their accuracy believe in the theory of repression, which is discussed in a subsequent section of this article. According to this theory, memories for terrible events (especially of a sexual nature) can be repressed, or banished to an unconscious state. The memories may lie dormant for years, but with great effort and appropriate cues, they can be retrieved with relative accuracy. Critics point out that there is little evidence supporting the concept of repression, aside from some reports on individual cases. The critics believe that the processes that give rise to false memories—suggestion and imagination—may better explain the phenomenon of recovered memories.

Without corroborating evidence, there is no way to check the accuracy of recovered memories. Thus, even though people may sincerely believe they have recovered a memory of an event from their distant past, the event usually remains a matter of belief, not of fact. Because psychologists know so little about recovery of distant memories, even of normal experiences, the debate over recovered memories is not likely to be resolved soon. For more detail on the recovered memory controversy, see the sidebar “Recovered Memories and False Memories” in Encarta Encyclopedia Deluxe.

VI

WHY PEOPLE FORGET

Forgetting is defined as the loss of information over time. Under most conditions, people recall information better soon after learning it than after a long delay; as time passes, they forget some of the information. We have all failed to remember some bit of information when we need it, so we often see forgetting as a bother. However, forgetting can also be useful because we need to continually update our memories. When we move and receive a new telephone number, we need to forget the old one and learn the new one. If you park your car every day on a large lot, you need to remember where you parked it today and not yesterday or the day before. Thus, forgetting can have an adaptive function.

A

Rate of Forgetting

Hermann Ebbinghaus

German philosopher Hermann Ebbinghaus conducted some of the first scientific experiments on human memory.

Corbis

The subject of forgetting is one of the oldest topics in experimental psychology. German philosopher Hermann Ebbinghaus initiated the scientific study of human memory in experiments that he began in 1879 and published in 1885 in his book, On Memory. Ebbinghaus developed an ingenious way to measure forgetting. In order to avoid the influence of familiar material, he created dozens of lists of nonsense syllables, which consisted of pronounceable but meaningless three-letter combinations such as XAK or CUV. He would learn a list by repeating the items in it over and over, until he could recite the list once without error. He would note how many trials or how long it took him to learn the list. He then tested his memory of the list after an interval ranging from 20 minutes to 31 days. He measured how much he had forgotten by the amount of time or the number of trials it took him to relearn the list. By conducting this experiment with many lists, Ebbinghaus found that the rate of forgetting was relatively consistent. Forgetting occurred relatively rapidly at first and then seemed to level off over time (see the accompanying chart entitled “Forgetting Curve”). Other psychologists have since confirmed that the general shape of the forgetting curve holds true for many different types of material. Some researchers have argued that with very well learned material, the curve eventually flattens out, showing no additional forgetting over time.

Duration of Working Memory

People rapidly forget information in working memory if they do not attend to it. This graph shows the results of a study in which subjects heard an experimenter speak three letters. The subjects were directed to repeat back the letters after being distracted by another task during a short interval. The longer the delay, the less likely people were to recall the letters.

© Microsoft Corporation. All Rights Reserved.

Ebbinghaus’s forgetting curve illustrated the loss of information from long-term memory. Researchers have also studied rate of forgetting for short-term or working memory. In one experiment, subjects heard an experimenter speak a three-letter combination (such as CYG or FTQ). The subjects’ task was to repeat back the three letters after a delay of 3, 6, 9, 12, 15, or 18 seconds. To prevent subjects from mentally rehearsing the letters during the delay, they were instructed to count backward by threes from a random three-digit number, such as 361, until signaled to recall the letters. As shown in the accompanying chart entitled “Duration of Working Memory,” forgetting occurs very rapidly in this situation. Nevertheless, it follows the same general pattern as in long-term memory, with sharp forgetting at first and then a declining rate of forgetting. Psychologists have debated for many years whether short-term and long-term forgetting have similar or different explanations.

B

Decay Theory of Forgetting

The oldest idea about forgetting is that it is simply caused by decay. That is, memory traces are formed in the brain when we learn information, and they gradually disintegrate over time. Although decay theory was accepted as a general explanation of forgetting for many years, most psychologists do not lend it credence today for several reasons. First, decay theory does not really provide an explanation of forgetting, but merely a description. That is, time by itself is not a causative agent; rather, processes operating over time cause effects. Consider a bicycle left out in the rain that has rusted. If someone asked why it rusted, he or she would not be satisfied with the answer of “time out in the rain.” A more accurate explanation would refer to oxidation processes operating over time as the cause of the rusty bicycle. Likewise, memory decay merely describes the fact of forgetting, not the processes that cause it.

The second problem for decay theory is the phenomenon of reminiscence, the fact that sometimes memories actually recover over time. Experiments confirm an observation experienced by most people: One can forget some information at one point in time and yet be able to retrieve it perfectly well at a later point. This feat would be impossible if memories inevitably decayed further over time. A final reason that decay theory is no longer accepted is that researchers accumulated support for a different theory—that interference processes cause forgetting.

C

Interference Theory of Forgetting

Forgetting in Sleep and Waking

In a 1924 experiment, students recalled lists of nonsense syllables better when they were tested after a period of sleep than when they were tested after an interval of waking. The results support the conclusion that a major source of forgetting is interference from other information over time.

© Microsoft Corporation. All Rights Reserved.

According to many psychologists, forgetting occurs because of interference from other information or activities over time. A now-classic experiment conducted in 1924 by two American psychologists, John Jenkins and Karl Dallenbach, provided the first evidence for the role of interference in forgetting. The experimenters enlisted two students to learn lists of nonsense syllables either late at night (just before going to bed) or the first thing in the morning (just after getting up). The researchers then tested the students’ memories of the syllables after one, two, four, or eight hours. If the students learned the material just before bed, they slept during the time between the study session and the test. If they learned the material just after waking, they were awake during the interval before testing. The researchers’ results are shown in the accompanying chart entitled, “Forgetting in Sleep and Waking.” The students forgot significantly more while they were awake than while they were asleep. Even when wakened from a sound sleep, they remembered the syllables better than when they returned to the lab for testing during the day. If decay of memories occurred automatically with the passage of time, the rate of forgetting should have been the same during sleep and waking. What seemed to cause forgetting was not time itself, but interference from activities and events occurring over time.

There are two types of interference. Proactive interference occurs when prior learning or experience interferes with our ability to recall newer information. For example, suppose you studied Spanish in tenth grade and French in eleventh grade. If you then took a French vocabulary test much later, your earlier study of Spanish vocabulary might interfere with your ability to remember the correct French translations. Retroactive interference occurs when new information interferes with our ability to recall earlier information or experiences. For example, try to remember what you had for lunch five days ago. The lunches you have had for the intervening four days probably interfere with your ability to remember this event. Both proactive and retroactive interference can have devastating effects on remembering.

D

Repression

Another possible cause of forgetting resides in the concept of repression, which refers to forgetting an unpleasant event or piece of information due to its threatening quality. The idea of repression was introduced in the late 19th century by Austrian physician Sigmund Freud, the founder of psychoanalysis. According to Freudian theory, people banish unpleasant events into their unconscious mind. However, repressed memories may continue to unconsciously influence people’s attitudes and behaviors and may result in unpleasant side effects, such as unusual physical symptoms and slips of speech. A simple example of repression might be forgetting a dentist appointment or some other unpleasant daily activity. Some theorists believe that it is possible to forget entire episodes of the past—such as being sexually abused as a child—due to repression. The concept of repression is complicated and difficult to study scientifically. Most evidence exists in the form of case studies that are usually open to multiple interpretations. For this reason, many memory researchers are skeptical of repression as an explanation of forgetting, although this verdict is by no means unanimous. For further information on repressed memories, see the sidebar “Recovered Memories and False Memories” that accompanies this article.

VII

BIOLOGICAL BASIS OF MEMORY

One of the most exciting topics of scientific investigation lies in cognitive neuroscience: How do physical processes in the brain give rise to our psychological experiences? In particular, a great deal of research is trying to uncover the biological basis of learning and memory. How does the brain code experience so that it can be later remembered? Where do memory processes occur in the brain?

In the early and mid-1900s, psychologists engaged in the “search for the engram.” They used the term engram to refer to the physical change in the nervous system that occurs as a result of experience. (Today most psychologists use the term memory trace to describe the same thing.) The researchers hoped to find some particular location in the brain where memories were stored. This early work, conducted mostly with animals, failed to find a specific locus of memory in the brain. For example, American psychologist Karl Lashley trained rats to solve a maze, then surgically removed various parts of the rats’ brains. No matter what part of the brain he removed, the rats always retained at least some ability to solve the maze. From such research, psychologists concluded that memory is distributed across the brain, not localized in one place.

A

Brain Structures Involved in Memory

Brain Activity in Memory

Positron emission tomography (PET) scans reveal brain regions involved in memory. Left, an encoding task (the initial processing of information into memory) activates the left prefrontal cortex. Right, an attempt to retrieve memories activates the right prefrontal cortex.

Courtesy of Dr. Shitij Kapur, MD, PhD; University of Toronto

Modern research confirms the hypothesis that memories are not localized in one place in the brain, but rather involve interacting circuits operating across the brain. Many of the neural regions used in perceiving and attending to information seem also to be involved in the encoding and subsequent retrieval of information. Thus, although different brain regions perform different memory-related processes, the memories themselves do not appear to reside in any particular place.

The hippocampus is thought to be one of the most important brain structures involved in memory. The case of the patient H.M. (only his initials were used to preserve his anonymity), one of the most famous case studies in neuropsychology, strikingly demonstrates the importance of the hippocampus. In 1953, as a 27-year-old man, H.M. underwent brain surgery to control severe epileptic seizures. The surgeons removed his medial temporal lobes, which included most of the hippocampus, the amygdala, and surrounding structures. Although the operation successfully controlled H.M.’s seizures, it had an altogether unexpected and devastating side effect: H.M. was unable to form new long-term memories in a way that he could later retrieve them. That is, he could not remember anything that happened to him after the surgery. His memory of events prior to the surgery was mostly intact, and his reasoning and thinking skills remained strong. But he could not remember meeting new people or new experiences for more than a few minutes. Researchers concluded that the hippocampus and its surrounding structures in the medial temporal lobe play a critical role in the encoding of episodic memories, especially in binding elements of memories together to locate the memories in particular times and places.

Limbic System

The limbic system is a group of brain structures that play a role in memory, emotion, and motivation. The hippocampus and surrounding structures are thought to play crucial roles in the encoding and retrieval of memories. The amygdala, a structure that helps to regulate emotion, seems to play a role in emotional memories.

© Microsoft Corporation. All Rights Reserved.

Further evidence for the importance of the hippocampus and other regions of the brain in human memory has been provided by advanced brain imaging techniques, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). Brain imaging methods allow researchers to see the activity of the living human brain on a computer screen as a person engages in different types of cognitive tasks, such as reading, solving math problems, or memorizing a list of words. These scanning methods take advantage of the fact that when a brain region becomes active, the rate at which neurons (brain cells) fire increases within this region. Increased neuronal firing in a region causes an increase in blood flow to that region, which the scanners can measure. Therefore, if a person is encoding new information into memory and the hippocampus is active during encoding, we would expect to see increased blood flow to the hippocampus. This is exactly the pattern observed in most studies.

Neuroimaging techniques have revealed other brain regions involved in memory. The frontal lobes play an important role in encoding and retrieving memories. For example, certain areas of the left frontal lobe seem especially active during encoding of memories, whereas those in the right frontal lobe are more active during retrieval. An area in the right anterior prefrontal cortex becomes active when a person is trying to retrieve a previously experienced episode. Some evidence indicates that this region may be even more active when the retrieval attempt is successful—that is, when the person not only attempts to remember but is able to remember some previous occurrence.

For more information on brain imaging methods, See also Brain: Brain Imaging.

B

Biochemistry of Memory

The study of the biochemistry of memory is another exciting scientific enterprise, but one that can only be touched upon here. Scientists estimate that an adult human brain contains about 100 billion neurons. Each of these is connected to hundreds or thousands of other neurons, forming trillions of neural connections. Neurons communicate by chemical messengers called neurotransmitters. An electrical signal travels along the neuron, triggering the release of neurotransmitters at the synapse, the small gap between neurons. The neurotransmitters travel across the synapse and act on the next neuron by binding with protein molecules called receptors. Most scientists believe that memories are somehow stored among the brain’s trillions of synapses, rather than in the neurons themselves.

Scientists who study the biochemistry of learning and memory often focus on the marine snail Aplysia because its simple nervous system allows them to study the effects of various stimuli on specific synapses. A change in the snail’s behavior due to learning can be correlated with a change at the level of the synapse. One exciting scientific frontier is discovering the changes in neurotransmitters that occur at the level of the synapse.

Other researchers have implicated glucose (a sugar) and insulin (a hormone secreted by the pancreas) as important to learning and memory. Humans and other animals given these substances show an improved capacity to learn and remember. Typically, when animals or humans ingest glucose, the pancreas responds by increasing insulin production, so it is difficult to determine which substance contributes to improved performance. Some studies in humans that have systematically varied the amount of glucose and insulin in the blood have shown that insulin may be the more important of the two substances for learning.

Scientists also have examined the influence of genes on learning and memory. In one study, scientists bred strains of mice with extra copies of a gene that helps build a protein called N-methyl-D-aspartate, or NMDA. This protein acts as a receptor for certain neurotransmitters. The genetically altered mice outperformed normal mice on a variety of tests of learning and memory. In addition, other studies have found that chemically blocking NMDA receptors impairs learning in laboratory rats. Future discoveries from genetic and biochemical studies may lead to treatments for memory deficits from Alzheimer’s disease and other conditions that affect memory.

VIII

MEMORY IMPAIRMENT: THE AMNESIAS

Amnesia means loss of memory. There are many different types of amnesias, but they fall into two major classes according to their cause: functional amnesia and organic amnesia. Functional amnesia refers to memory disorders that seem to result from psychological trauma, not an injury to the brain. Organic amnesia involves memory loss caused by specific malfunctions in the brain. Another type of amnesia is infantile amnesia, which refers to the fact that most people lack specific memories of the first few years of their life.

A

Functional Amnesia

Severe psychological trauma can sometimes cause functional amnesia. People with functional amnesia seem to have nothing physically wrong with their brain, even though the traumatic event presumably affects their brain in some way. In dissociative amnesia (sometimes called limited amnesia), a person loses memory of some important past experiences. For example, a person victimized by a crime may lose his or her memory for the event. Soldiers returning from battle sometimes experience similar symptoms.

Another type of functional amnesia is dissociative fugue, also referred to as functional retrograde amnesia. People with this disorder have much more extensive forgetting that may obscure their whole past. They commonly forget their personal identity and personal memories, and they often unexpectedly wander away from home. Typically the fugue state ends by itself within a few days or weeks. Often, after recovery the individual fails to remember anything that occurred during the fugue state.

Dissociative identity disorder, also called multiple personality disorder, is a type of amnesia in which a person appears to have two or more distinct personal identities. These identities alternate in their control of the individual’s conscious experiences, thoughts, and actions. In many cases, the person’s primary identity cannot recall what happened while the individual was controlled by another identity.

Although functional amnesias are a recurrent theme of television shows and movies, relatively few well-documented cases exist in the scientific literature. Most experts believe that these conditions do exist, but that they are exceedingly rare.

B

Organic Amnesia

Amnesia from Head Injury

British boxer Nigel Benn lands a punch to the head of American boxer Gerald McClellan during a 1995 fight in London. McClellan suffered severe brain damage in the fight that left him blind and that impaired his ability to form new memories and access long-term memories.

Chris Laurens/FSP/Liaison Agency

Organic amnesia refers to any traumatic forgetting that is produced by specific brain damage. Typically, these amnesias occur as part of brain disorders caused by tumors, strokes, head trauma, or degenerative diseases, such as Alzheimer’s disease. However, certain psychoactive drugs (drugs affecting mood or behavior) can cause amnesia, as can certain dietary deficiencies and electroconvulsive therapy for depression. Organic amnesias may be temporary or permanent. Amnesia resulting from a mild concussion or from electroconvulsive therapy is usually temporary, whereas severe head injuries may lead to permanent memory loss.

The case of the patient H.M., described earlier in this article, is an example of organic amnesia. In 1953 brain surgery for epilepsy left H.M. with dramatic anterograde amnesia, meaning he was unable to remember new information and events that occurred after his operation. Somewhat surprisingly, this severe impairment in the ability to learn new information was accompanied by no detectable impairment in his general intellectual ability or in his ability to use or understand language. H.M. also showed some retrograde amnesia, or inability to remember events before the onset of the surgery. For example, he could not recall that his favorite uncle had died three years earlier. Still, most of his general knowledge was intact, and he performed well on a test of famous faces (of people who had become famous prior to 1950).

Studies of H.M. and other amnesic patients have provided surprising insights into the workings of memory. One remarkable finding is that even though H.M. had severe anterograde amnesia, he (and other amnesic patients like him) still performed normally on tests of implicit memory. For example, H.M. could learn new motor skills, even though he would have no conscious memory of doing so. Even in dense, or severe, amnesias, not all memory abilities are impaired. For more information on implicit memory, see the Implicit Memory section of this article.

Korsakoff’s syndrome, also called Korsakoff’s psychosis, is a disorder that produces severe and often permanent amnesia. In this condition, years of chronic alcoholism and thiamine (vitamin B₁) deficiency cause brain damage, particularly to the thalamus, which helps process sensory information, and to the mammillary bodies, which lie beneath the thalamus. Some patients also have damage to the cortex and cerebellum. Korsakoff’s patients show severe anterograde amnesia, or difficulty learning anything new. In addition, most suffer from retrograde amnesia ranging from mild to severe and typically cannot remember recent experiences. The condition is also associated with other intellectual deficits, such as confusion and disorientation. Korsakoff’s syndrome is named after Sergei Korsakov (Korsakoff), the Russian neurologist who first described it in the late 19th century.

Amnesia also occurs in Alzheimer’s disease, a condition in which the neurons in the brain gradually degenerate, hindering brain function. Damage to the hippocampus and frontal lobes impairs memory. Many other types of organic amnesias exist. For example, in large doses, most depressant drugs can cause acute loss of memory. With severe alcohol or marijuana intoxication, people often forget events that occurred while under influence of the drug.

C

Infantile Amnesia

Infantile amnesia, also called childhood amnesia, refers to the fact that people can remember very little about the first few years of their life. Surveys have shown that most people report their earliest memory to be between their third and fourth birthdays. Furthermore, people’s memories of childhood generally do not become a continuous narrative until after about seven years of age.

Psychologists do not know what causes infantile amnesia, but they have several theories. One view is that brain structures critical to memory are too immature during the first few years of life to record long-term memories. Another theory is that children cannot remember events that occurred before they mastered language. In this view, language provides a system of symbolic representation by which people develop narrative stories of their lives. Such a narrative framework may be necessary for people to remember autobiographical events in a coherent context.

The phenomenon of infantile amnesia does not mean that infants and young children cannot learn. After all, babies learn to stand, walk, and talk. Scientific evidence indicates that even young infants can learn and retain information well. For example, one experiment found that three-month-old babies could learn that kicking their legs moves a mobile over their crib. Up to a month later, the babies could still demonstrate their knowledge that kicking moved the mobile. Infants and toddlers seem to retain implicit memories of their experiences.

IX

EXCEPTIONAL MEMORY

All people differ somewhat in their ability to remember information. However, some individuals have remarkable memories and perform feats that normal individuals could never hope to achieve. These individuals, sometimes called mnemonists (pronounced “nih-MAHN-ists”), are considered to have exceptional memory.

Psychologists have described several cases of exceptional memory. Aleksandr R. Luria, a Russian neuropsychologist, described one of the most famous cases in his book The Mind of a Mnemonist (1968). Luria recounted the abilities of S. V. Shereshevskii, a man he called S. Luria studied Shereshevskii over many years and watched him perform remarkable memory feats. However, until Luria began studying these feats, Shereshevskii was unaware of how extraordinary his talents were. For example, Shereshevskii could study a blackboard full of nonsense material and then reproduce it at will years later. He could also memorize long lists of nonsense syllables, extremely complex scientific formulas, and numbers more than 100 digits long. In each case, Shereshevskii could recall the information flawlessly, even if asked to produce it in reverse order. Luria reported one instance in which Shereshevskii was able to recall a 50-word list when the test was given without warning 15 years after presentation of the list! He recalled all 50 words without a single error.

The primary technique Shereshevskii used was mental imagery. He generated very rich mental images to represent information. In addition, part of his ability might have been due to his astonishing capacity for synesthesia. Synesthesia occurs when information coming into one sensory modality, such as a sound, evokes a sensation in another sensory modality, such as a sight, taste, smell, feel, or touch. All people have synesthesia to a slight degree. For example, certain colors may “feel” warm or cool. However, Shereshevskii’s synesthesia was extremely vivid and unusual. For example, Shereshevskii once told a colleague of Luria’s, “What a crumbly yellow voice you have.” He also associated numbers with shapes, colors, and even people. Synesthetic reactions probably improved Shereshevskii’s memory because he could encode events in a very elaborate way. But they often caused him confusion, too. For example, reading was difficult because each word in a sentence evoked its own mental image, interfering with comprehension of the sentence as a whole.

A second case of exceptional memory illustrates the talent some people display for remembering certain types of material. In a series of tests in the 1980s and 1990s, Rajan Srinavasen Mahadevan (known as Rajan) demonstrated a remarkable talent for remembering numbers, but for other types of material, his memory ability tested in the normal range. Rajan memorized the mathematical ratio pi, which begins 3.14159 and continues indefinitely with no known pattern, to nearly 32,000 decimal places! If given a string of digits, within a few seconds he could accurately say whether or not the string appears in the first 32,000 digits of pi. He could also rapidly identify any of the first 10,000 digits of pi when given a specific decimal place. For example, he could tell what digit is in decimal place 6,243 in about 12 seconds, and he rarely made errors on this task. Rajan demonstrated great skill at learning new numerical information.

Shereshevskii and Rajan scored in the normal range on standard intelligence tests. Another group of people, those with savant syndrome (formerly called idiot savants), usually score low on intelligence tests but have one “island” of outstanding cognitive ability. Many children and adults who are deemed savants have extraordinary memory. Psychologists have studied many cases of savant syndrome, but its nature remains a mystery.

Cases of exceptional memory stand as remarkable puzzles whose implications for normal memory functioning are unclear. In some cases the remarkable talents exemplify techniques (such as mental imagery) that are known to magnify normal memory ability. These striking cases have not been integrated well into the scientific study of memory, but generally stand apart as curiosities that cannot yet be explained in any meaningful way.

X

WAYS TO IMPROVE MEMORY

Memory improvement techniques are called mnemonic devices or simply mnemonics. Mnemonics have been used since the time of the ancient Greeks and Romans. In ancient times, before writing was easily accomplished, educated people were trained in the art of memorizing. For example, orators had to remember points they wished to make in long speeches. Many of the techniques developed thousands of years ago are still used today. Modern research has allowed psychologists to better understand and refine the techniques.

All mnemonic devices depend upon two basic principles discussed earlier in this article: (1) recoding of information into forms that are easy to remember, and (2) supplying oneself with excellent retrieval cues to recall the information when it is needed. For example, many schoolchildren learn the colors of the visible spectrum by learning the imaginary name ROY G. BIV, which stands for red, orange, yellow, green, blue, indigo, violet. Similarly, to remember the names of the Great Lakes, remember HOMES (Huron, Ontario, Michigan, Erie, and Superior). Both of these examples illustrate the principle of recoding. Several bits of information are repackaged into an acronym that is easier to remember. The letters of the acronym serve as retrieval cues that enable recall of the desired information.

Psychologists and others have devised much more elaborate recoding and decoding schemes. Three of the most common mnemonic techniques are the method of loci, the pegword method, and the PQ4R method. Research has shown that mnemonic devices such as these permit greater recall than do strategies that people usually use, such as ordinary rehearsal (repeating information to oneself).

A

Method of Loci

One of the oldest mnemonics is the method of loci (loci is a Latin word meaning “places”). This method involves forming vivid interactive images between specific locations and items to be remembered. The first step is to learn a set of places. For instance, you might familiarize yourself with various locations around your house: the front sidewalk, the front doorstep, the front door, the foyer and so on. Once you have permanently memorized the locations, you can then use them to recode experiences for later recall. You can use the method of loci to remember any set of information, such as a grocery list or points in a speech. The best strategy is to convert each item of information into a vivid mental image by putting it at a familiar location where it can be “seen” in the mind. So, for example, you might remember a grocery list as bread on the front sidewalk, milk on the front porch, bananas hanging from the front door, and so on. When you are at the grocery store and need to remember the list, you can mentally walk through the house and see what object is in each spot. The locations serve as retrieval cues for the desired information. Although this technique may seem far-fetched, with a little practice it can prove quite effective. In fact, the amount of information one can remember using this method is limited only by the number of locations one has memorized.

B

Pegword Method

Pegword Mnemonic

The pegword mnemonic is a method of remembering things through visual imagery. The more bizarre the images are, the more likely you will recall them.

© Microsoft Corporation. All Rights Reserved.

Another mnemonic that relies on the power of visual imagery is called the pegword method. There are many variations on the pegword method, but they are all based on the same general principle. People learn a series of words that serve as “pegs” on which memories can be “hung.” In one popular scheme, the pegwords rhyme with numbers to make the words easy to remember: One is a gun, two is a shoe, three is a tree, four is a door, five is a hive, six is sticks, seven is heaven, eight is a plate, nine is wine, and ten is a hen. To learn the same grocery list, one might associate gun and bread by imagining the gun shooting the bread. Two is a shoe, so one would imagine a milk carton sitting in a giant shoe, and so on. When you need to remember the list of groceries, you simply recall the pegwords associated with each number; the pegwords then serve as retrieval cues for the groceries. Peg methods such as this one permit more flexible access to information than does the method of loci. For example, if you want to recite the items backwards for some reason, you can do so just as easily as in the forward direction. If you need to know the eighth item, you can say “eight is a plate” and mentally look at your image for the item on the plate.

C

PQ4R Method

The PQ4R method is a mnemonic technique used for remembering text material. The name is itself a mnemonic device for the steps involved. If you are interested in better remembering a chapter from a textbook, you should first Preview the information by skimming quickly through the chapter and looking at the headings. The next step is to form Questions about the information. One way to do this is by simply converting headings to questions. Using this article as an example, you might ask, “What are the ways to improve memory?” The third step is to Read the text carefully trying to answer the questions. After reading, the next step is to Reflect on the material. One way would be to create your own examples of how the principles you are reading could be applied. The next step is to Recite the material after reading it. That is, put the book aside or look away and try to recall or to recite what you have just read. If you cannot bring it to mind now, you will have little chance later. The last step in PQ4R is to Review. After you have read the entire chapter, go through it again trying to recall and to summarize its main points.

Tests of the PQ4R method of reading text material have shown its advantages over the way people normally read. However, PQ4R method slows reading considerably, so students may not use the technique, even though it is more effective. Most mnemonic devices involve additional work, but they are well worth the investment for improving memory.

D

Other Techniques

The principles of encoding, recoding, and retrieval discussed elsewhere in this article suggest other ways that memory can be improved. For example, encoding information in an elaborate, meaningful way helps in retention. There are many ways to encode information meaningfully. When possible, try to convert verbal information into mental images. When learning about events and facts, try to focus on their meaning rather than their superficial characteristics. Relating new information to your personal experiences or to what you already know also makes it easier to retain the information.

Spacing out study sessions is another way to improve your memory. That is, if you are going to read a chapter twice before a test, retention is better if you allow some time to pass between readings, instead of reading the chapter twice in one sitting. Overall, spaced learning or spaced practice (learning opportunities that are spread out in time) is better than massed practice (back-to-back practice, in immediate succession) for retaining facts and skills over longer intervals. However, if a test occurs soon after learning, massed practice is as good as or better than spaced practice.

If you are having difficulty retrieving facts from your memory, try to remember the setting in which you originally learned them. This advice capitalizes on the encoding specificity principle. The more similar the retrieval environment is to the learning environment, the easier it will be to retrieve the information learned.