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Book Review

Searching for Memory
the brain, the mind, and the past


by Daniel Schacter
New York: Basic Books, 1996

 

 

There is scarcely a human activity that is not affected by memory. To overestimate the importance of studies on memory seems impossible. Yet, all too often, we take memory for granted and make assumptions about memory without knowing whether our beliefs are based on fact or myth. Most of us can be excused for our ignorance, since studies of memory rarely attract the attention of the mass media. There are some notable exceptions, such as the "Memory Wars", as Schacter refers to the battle over recovered repressed memories of alien abductions or of childhood abuse and murder. Daniel Schacter makes accessible to the general reader the background information necessary to make sense of the "Memory Wars." (He devotes an entire chapter to the issue.) He provides an invaluable map of where we are in the quest to understand one of the most fundamental properties of the human mind. And he dispels a few myths along the way.

Some readers might be disappointed to find out that we don't really know how memory works. There is no universally agreed upon model of the mind/brain, and no universally agreed upon model of how memory works. Two models popular with materialists, the behaviorist model and that of cognitive psychology (the brain as computer), are rejected by Schacter because they cannot account for the subjective and present-need basis of memory. Lest dualists get their hopes up, Schacter's concern for a model which does justice to subjectivity has nothing to do with a concern for a "transcendental unity of apperception" or a "self" to be distinguished from the self's memories. Subjectivity in remembering, he says, involves at least three important factors. One, memories are constructions made in accordance with present needs, desires, influences, etc. Two, memories are often accompanied by feelings and emotions. Three, memory usually involves the rememberer's awareness of the memory. A good model of how memory works must not only fit with scientific knowledge but also fit with the subjective nature of memory.

In chapter two, "Building Memories," Schacter presents a sketch of a model which incorporates elements of both a neurological and a psychological model of memory. He notes that there should only be one correct neurological model (N-model), a model of how the brain and neural network function in memory, a descriptive model of functions and causal connections. But there may be several psychological models (P-models) of memory, though each of them must be true to the N-model, as well as to subjective experience, to be adequate. P-models are explanatory models, trying to help us make sense out of the experiences of remembering and forgetting.

For example, one P-model sees memory as a present act of consciousness, reconstructive of the past, stimulated by an analogue of an engram called the "retrieval cue." The engram is the neural network representing fragments of past experience. Schacter elaborates throughout his book on studies supporting the notion that memories are reconstructions of the past and might better be thought of as a collage or a jigsaw puzzle than as "tape recordings," "pictures" or "video clips" stored as wholes. On this model, perceptual or conscious experience does not record all sense data experienced. Most sense data is not stored at all. What is stored are rather bits and fragments of experience which are encoded in engrams. Exactly how they are encoded is not completely understood, but what progress has been made in understanding the complexities of neural encoding is set out by Schacter in various chapters. For example, he discusses Wilder Penfield's experiments done in the 1950's which involved placing electrodes on the surface of the exposed temporal lobes of patients. He was able to elicit "memories" in 40 of 520 patients. Many psychologists (and lay people) refer to these experiments as proof that memories are stored in specific places and that even though we may not remember much of our past, the right stimulus would evoke a memory of things long forgotten. In a survey of psychologists by Loftus and Loftus, 84% said they believe every experience is permanently stored in the mind. [p. 76] Maybe so, but Schacter points out that the Penfield experiments are not very good evidence for this belief. Not only could Penfield only elicit "memories" in about 1 out of every 8 patients, he did not provide support for the claim that what was elicited was actually a memory and not a hallucination, fantasy or confabulation.

Other studies indicate that encoding involves various connections between different parts of the brain. In fact, what is being discovered is that there are distinct types and elements of memory which involve different parts of the brain. I will not attempt to report on any of those discoveries here, but the reader should be prepared to take a journey inside the brain. I will say, however, that Schacter does an excellent job of not getting overtechnical or burdening the reader with extraneous jargon. There is a lot of jargon used in his discussions of neuroscience and psychology, but in my view it is neither burdensome nor unneeded.

On the P-model described in the previous paragraph, forgetting is due either to weak encoding, to lack of a retrieval cue, to time and the replacement in the neural network by later experiences, to repetitive experiences (you'll remember the one special meal you had at a special restaurant, but you won't remember what you had for lunch a year ago Tuesday), or to keep us from going crazy. (Imagine never forgetting anything, actually achieving the stated goal of L. Ron Hubbard's dianetics: reaching the state of "the clear." His followers should read Jorge Luis Borges "Funes, the Memorious," a story about such a being.) The chances of remembering something improve by "consolidation," creating strong encoding. Thinking and talking about an experience enhances the chances of remembering it. One of the more well-known techniques of remembering involves the process of association. For example, today I attended a meeting which involved a discussion of security procedures. The phone number extension of the campus police was given. Such a number is easy to remember if associations are made. Most of us can remember a phone number long enough to dial it, but when you want to remember a phone number, even a 4-digit extension, six months or a year from now without ever having dialed the number, the task gets more difficult. In this case, the number is 2365. All our campus extensions begin with 2, so I only need to remember 3 digits. In this case, the three digits, 365, is the number of days in a year. Thus, if I reinforce the association with the days of the year--by occasionally reminding myself of the association when I look at the calendar--I think I'll remember the extension of the campus police a year or even five years from now.

The daily amnesia most of us suffer, awakening after a night of dreams but unable to remember any of them, is a bit more complex but weak encoding is at work here, too. Most of us can remember a dream which occurred just before awakening, but find that later in the day we've lost all memory of the dream. To remember dreams, some suggest that you get up immediately and write down the dream. An easier method is to stay in bed and create some associations. The easiest association is to give your dream a title and a purposive description. I tried this for a few nights and found that I could remember the title and the dream later in the day. I began writing the title of the dream down and then a brief description of what I thought the dream suggested. For example, I entitled one dream "The Mailbox" and described its purpose as "write to J.B." That little bit of information serves as a retrieval cue and I can now remember the dream: I am standing in front of a large number of mailboxes, the type they have at post offices or in department mail rooms. Next to me is a friend I've known since grammar school but haven't seen in ten or fifteen years. I notice that his brother also has a mailbox and indicate my surprise that R. is on the staff, too. My friend and I are obviously colleagues in the dream. J.B. says to me that R. isn't really on the staff; he works at the Shell gasoline station. The dream occurred during the Christmas holidays. I used to hear from J.B. at Christmas time...usually one of those form letters telling us about the kids, etc., but I haven't heard from him in several years. I took my dream to reflect some sort of uneasiness about the lack of communication between an old friend and myself and as a suggestion to write J.B. a letter and reestablish communication. (I have no idea what the part about his brother and the Shell station means. I knew his brother fairly well and there's no chance I was connecting the news stories about Shell executives being racists and J.B.'s brother. No one in J.B.'s family was bigoted or prejudiced to my knowledge.) Anyway, the point is that I have little doubt that I would have completely forgotten the dream if I had not given it a title and a description and then later on wrote down both and tried to recall the details. (I must admit that I had forgotten the dream and the details until I looked at my notes which contain only the five words mentioned above. If I had written to J.B., I doubt that I would have forgotten the dream, for that activity would have been one more element of elaborate encoding of the memory.)

Of more interest than my dream is the discussion of Jonathan Winson's theory that during REM sleep, the brain is consolidating and strengthening some memories while discarding others. The hippocampus may be playing back experiences to various cortical regions where it will eventually be permanently stored. [p. 88]

In addition to dream amnesia, Schacter has much to say about other kinds of amnesia, including the kinds of cases which neurologist Oliver Sacks is famous for writing about. The effects of alcohol, brain injuries and physical or psychological traumas on memory are exemplified with case studies such as the Russian scientist who could remember his childhood but not his recent past. (He'd written an autobiography, so the accuracy of his childhood memories could be checked.) There is also the case of psychogenic amnesia of a man Schacter calls Lumberjack. He was a young man who didn't know who he was, who was found wandering the streets of Toronto. He could not remember anything of his past except the word Lumberjack and a few other details from a period in his life about one year prior to when he was found. He was in what psychiatrists call a fugue state. His amnesia had been triggered by his grandfather's death and was spontaneously cleared up while watching a television program depicting a funeral and a cremation.

One type of amnesia, what Schacter calls limited amnesia, is quite common. Limited amnesia occurs in people who suffer a severe physical or psychological trauma and are unable to remember the event. Several such cases are described by Schacter as he explores the possibility of a link between the different kinds of experiences which result in limited amnesia, as well as the connection between trauma-induced amnesia and the unconscious mind.

On the amnesia claimed for repressed memories, which has become popular with certain therapists in recent years, Schacter devotes a whole chapter. Repressed memory therapists have failed to provide an adequate model of memory to account for what they claim is happening in repression. The idea that all of us have memories we can't access, but which are causing mental and physical illnesses, is a popular one. The idea that some experiences are so traumatic that as a defense mechanism we suppress the thought of such experiences has been repeated so often as to be considered a fact by many people. But is it? Schacter does not think so. The scientific evidence for repression is weak. Even weaker is the evidence that specific disorders are caused by repression of specific kinds of experiences, such as the experience of sexual abuse. Unlike cases of amnesia which involve alcohol, drugs, brain injury or disease, or psychological trauma, the cases involving repressed memories often depend on whether the patient really suffers from amnesia. The repressed memory therapists seem to start with the assumption that most of their patients suffer from amnesia, but the amnesia is very specific and always involves just the kind of thing most people would remember. On the other hand, there are cases where the amnesia is not in doubt, and the evidence indicates that some sort of implicit memory exists which is troubling to the amnesiac. Schacter notes the case of a rape victim who could not remember the rape which took place on a brick pathway. The words brick and path kept popping into her mind, but she did not connect them to the rape. And she became very upset when taken back to the scene of the rape, though she didn't remember what had happened there. [p. 232]

One of the more interesting areas of discussion in the "Memory Wars" is that of memory distortion. The distortion can be a distortion of attitude, whereby a present mood or emotion invades a memory and imbues it with one's present emotive state even though the original experience was not colored by the same mood. (This is the obverse of trying to put yourself in a good mood by remembering some pleasant experiences from the past.) The distortion might be of the content, especially source distortion. E.g., you're robbed. The police show you a photo of a man and ask is this the man. You say that you're not sure. Later, in a line-up you positively identify the robber, who turns out to be the man whose photo you had been shown. It turns out that he could not have robbed you, because he was in jail at the time you were robbed. Your memory was distorted by the photo; you remembered the robber but the source was not your perception while being robbed, it was your perception of the photo shown to you by the police. Studies on source memory (recalling precisely when and where an event occurred) indicate that such distortion is not uncommon. Distortions can also be caused by making assumptions or drawing inferences which creep into our encoding and associations. [ch. 4]

Memory distortion is dramatically exemplified by Schacter in a simple experiment. Pay attention to the following series of words: candy, sour, sugar, bitter, good, taste, tooth, nice, honey, soda, chocolate, heart, cake, eat, and pie. After looking at the list, turn away and write down all the words you can remember from the list.

Now take the following test. consider the three words printed in italics at the end of this sentence and, without looking back to the previous paragraph, try to remember whether they appeared on the list....taste, point, sweet. [p. 103]

Between 80-90 percent of those tested by Schacter in the "sweet experiment" claim erroneously that sweet was on the original list. Many not only believe sweet was on the list, they claim to remember it vividly. Amnesic patients, on the other hand, made many fewer false recognitions than did healthy subjects. "This is because the amnesic patients did not successfully encode and retain the gist of the studied words. False recognition of sweet requires accurate retention of the general meaning of the words on the target list, which in turn depends on the hippocampus and other medial temporal lobe structures that are damaged in amnesic patients." [p. 104] But getting the gist of something does not guarantee that the details are remembered accurately. The implications of memory distortion can be enormous and are discussed at length by Schacter.

Schacter also takes up the issues of memory in children. If not misled, they give generally accurate info, though they have particularly poor source memory, perhaps due to their immature and undeveloped frontal lobes. [p. 128] He reminds us again and again of the fragility of memory and how it is often accompanied by an inappropriate feeling of absolute certainty. My favorite story here is the one regarding John Dean, President Nixon's White House counsel who was part of the Watergate coverup. Dean testified for days, giving enormous amounts of details to meetings that took place many months before his testimony. He seemed a veritable treasure trove of Watergate data. However, when the infamous tapes were discovered and played back, a comparison of what was actually said at the meetings and what Dean remembered as having been said, did not match up very well when it came to details. Hardly any of the details Dean testified to were correct, though he remembered general events pretty well, probably aided by his notes. [pp. 111-112]

Hypnosis and memory is another topic Schacter takes up. Studies on hypnosis show that hypnosis does nothing to enhance the accuracy of memory. Highly hynotizable people are vulnerable to creating illusory memories when given suggestions. Hypnosis, he says, "creates a retrieval environment that increases a person's willingness to call just about any mental experience a 'memory'." [p. 108] Hypnosis heightens a person's subjective confidence in the veracity and accuracy of memories, however. The distorting power of hypnosis over memory has been documented since Freud, but recent studies show that those hypnotized have fewer illusory memories when either (1) they have a poor rapport with the hypnotist; (2) when the subject is given an incentive to carefully distinguish between real and imaginary events and (3) when the subject is led to believe he or she will be able to make such distinctions when hypnotized.

There are many other topics which Schacter takes up. An entire chapter is devoted to the role of emotions in memory. Fascinating case studies are presented of people whose memories are like visions and direct and control their lives. He presents the results of his own studies in implicit memory (memory without awareness) and "priming," and the practical applications of those studies for developing programs using a "vanishing-cues procedure" for training brain damaged amnesiacs. [ch. 6] There are discussions throughout the book on various types of memory from the familiar short-term vs. long-term memory to distinctions between implicit/explicit memory; semantic/procedural/episodic memory; field/observer memory; lifetime/general event/event-specific memories; and more. Concepts such as "flashbacks", deja vu, and removing the effort to help remember something, are discussed, as is the topic of amnesia and dissociation (multiple personalities or dissociative identity disorder). In fact, the only topic not covered that I expected to be covered was "photographic memory."

Schacter has something to say to who wish to improve their memories and those who fear losing their memories as they grow old. You'll have to read the book to find out whether it would be worthwhile to invest in one of those memory courses advertised on infomercials. I'll only note that studies showed that people who could remember long lists of numbers by associating the numbers with familiar experiences or knowledge, could not carry over this ability to non-numerical tasks. As for the fear of losing memory with age, Schacter devotes his tenth and final chapter to the topic of aging and memory. I won't reveal what he says, but he does give this bit of advice: if you forget where you put your car keys, don't worry. If you forget you own a car, worry.

Finally, the book is illustrated throughout with works of art whose subject matter is some aspect of memory. Schacter collects such art and links the work of artists to that of scientists in an interesting and generally illuminating way.

Bob Carroll

January 18, 1997


further reading

repressed memory therapy The entry on The Skeptic's Dictionary discusses chapter nine, "The Memory Wars," of Searching for Memory. Daniel L. Schacter's Homepage

The Seven Sins of Memory: How the Mind Forgets and Remembers by Danile Schacter

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