Memory (psychology)

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

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.

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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.

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

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.

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.