Essentials of Human Memory (Classic Edition)

Alan Baddeley

• Editore: Psychology Press
• Anno: 2013
• ISBN:
  9781135068691
• Edizione: 1
• Argomento: Psychology
• Categoria: History & Theory in Psychology

This Classic Edition of the best-selling textbook offers an in-depth overview of approaches to the study of memory. With empirical research from both the real world and the neuropsychological clinic, the book explains the fundamental workings of human memory in a clear and accessible style.This edition contains a new introduction and concluding chapter in which the author reflects on how the book is organized, and also on how the field of memory has developed since it was first published.

Essentials of Human Memory evolved from a belief that, although the amount we know about memory has increased enormously in recent years, it is still possible to explain it in a way that would be fully understood by the general reader.

After a broad overview of approaches to the study of memory, short-term and working memory are discussed, followed by learning, the role of organizing in remembering and factors influencing forgetting, including emotional variables and claims for the role of repression in what has become known as the false memory syndrome. The way in which knowledge of the world is stored is discussed next, followed by an account of the processes underlying retrieval, and their application to the practical issues of eyewitness testimony. The breakdown of memory in the amnesic syndrome is discussed next, followed by discussion of the way in which memory develops in children, and declines in the elderly. After a section concerned with mnemonic techniques and memory improvement, the book ends with an overview of recent developments in the field of human memory.

Written by the leading expert in human memory, recently awarded the British Psychological Society Research Board Lifetime Achievement Award, Essentials of Human Memory will be of interest to students of Cognitive Psychology, Neuropsychology, and anyone with an interest in the workings of memory.

1

WHAT IS MEMORY?

‘I have a terrible memory.s’ How often have you heard that? In my own case, whenever I meet someone, and in casual conversation admit that I carry out research on memory, by far the most common response is ‘You should do some work on me—my memory is awful!s’ So is mine—I even managed to forget to turn up for a radio phone-in on memory. I was reminded of my dreadful lapse by reading the radio section of the newspaper, and arrived at the studio just in time to be asked by the anchor man for ‘a few tips on improving your memorys’!

I also believe, however, that I have a good memory, and would argue, despite its occasionally embarrassing fallibility, that both my memory and yours exceed that of the best computer in terms of capacity, flexibility, and durability. In the chapters that follow, I hope to persuade you to share my admiration.

Perhaps the best way to appreciate the importance of memory is to consider what it would be like to live without it, or rather without them, as memory is not a single organ like the heart or liver, but an alliance of systems that work together, allowing us to learn from the past and predict the future.

In recent years we have learned a great deal from the study of memory impairment following brain damage. Almost any damage to the brain will lead to some slowing in learning and some impairment in the speed with which we access old memories. Certain areas of the brain, however, are particularly crucial for memory. Serious damage to these can lead to dense amnesia, which can be a crippling handicap.

Consider the case of Clive Wearing, a talented musician and an expert on early music, who fell ill as a result of a viral infection (Wilson, Baddeley, & Kapur, 1995). The herpes simplex virus is carried by a large percentage of the population, typically having no worse effect than causing the occasional cold sore. On very rare occasions, however, the virus manages to overcome the brain's natural defences and cause an inflammation known as encephalitis. This can lead to extensive brain damage, and until relatively recently was often fatal. Although the disease can now be treated, patients often suffer extensive brain damage, which frequently leads to memory problems.

Clive Wearing is a particularly dramatic example of the terrible after-effects of encephalitis. He is so impaired that he cannot remember what happened more than minutes before, with the result that he is convinced that he has only just recovered consciousness. He keeps a diary which records this obsession—page upon page of records indicating the date, the time, and the fact that consciousness has just been regained. When confronted with evidence of earlier apparent conscious awareness, by being shown a video of himself, for example, he becomes upset and denies the evidence, even after many years of being in this condition. It is as if, faced with the enormity of a life limited to a horizon of a few seconds, he clings to the view that he has just recovered consciousness, with the implication that in the future all will be well.

Clive's world was very effectively portrayed in a television programme by Dr Jonathan Miller entitled ‘Prisoner of Consciousness’. Whenever his wife appears, Clive greets her with the joy appropriate to someone who has not seen a loved one for many months. She has only to leave the room for two or three minutes and return for the joy to be repeated, a process that is always full of emotion, and always expressed in the same way. Clive lives in a permanent present, unable to register change or to use the past to anticipate the future, a situation he once described as ‘Hell on earth. It's like being dead—all the bloody time.’

Clive's memory for his past is less dramatically impaired than his ongoing memory. Nevertheless it is severely disrupted—he knows who he is, and can give you a broad outline of his earlier life, but with very little accurate detail. He is not certain, for instance, whether his current, second, wife and he were married or not. He can remember, given appropriate prompts, certain highlights of his life, such as singing for the Pope during a papal visit to London or directing the first performance of Messiah in London with authentic instruments and decor. He had written a book on the early composer Lassus, but can remember virtually nothing about him. His visual memory is also impaired—he spent four years in Cambridge, but does not recognise a photograph of his old college. His general knowledge is similarly reduced—he has no idea, for example, as to the author of Romeo and Juliet.

There is, however, one area that is remarkably preserved, namely his musical skills. On one occasion his wife returned home to discover that his old choir was visiting him, and that he was conducting them just as he did in the old days. He can sight-read music and is able to accompany himself on the harpsichord, playing quite complex pieces and singing with great skill and feeling. Alas, he appears to find the transition from music back to his desolate state of amnesia particularly disturbing, with the result that music does not seem to provide the kind of solace that one might have hoped.

Clive has been in this state since 1985. He is still convinced that he has just woken up. He still lives in a desolate, eternal present. He cannot enjoy books because he cannot follow their plot, and takes no interest in current affairs because, likewise, they are meaningless as he does not remember their context. If he goes out, he immediately becomes lost. He is indeed a prisoner limited to a brief island of consciousness in the sea of amnesia.

The tragic case of Clive Wearing demonstrates that memory is important, but what is memory?

The physical basis of memory

It is often assumed by non-psychologists, and indeed by a few psychologists, that psychological theories should have the final aim of giving a physiological account of psychological facts. This view, which is sometimes called reductionism, sees a continuous chain of explanation extending down from psychology through physiology, biochemistry, and biophysics, to the subatomic particles studied by the physicist.

Suppose I were an architect and wanted to find out about London's St Paul's Cathedral. I could pursue my enquiries at many different levels. I could ask about the history of the building and how it came to be built following the Great Fire. I could ask about the style, and the influence of classical architecture on Sir Christopher Wren, who designed it. I could ask about its function, and I could ask about the details of the material that went into its construction. The viewpoint that a study of memory must begin with its biochemistry would be somewhat analogous to advocating that anyone interested in St Paul's Cathedral should begin by studying the atomic structure of brick and stone. There is no doubt that such a study would be relevant, and indeed if the atomic structure of the bricks had been inappropriate, the cathedral would never have remained standing. However, one could know everything about the atomic structure of brick and stone and yet know virtually nothing of interest about the cathedral. On the other hand, one could know a great deal about the cathedral without having any knowledge of the physio-chemical properties of brick and stone.

The structure of materials does of course at some point constrain the architect and obviously has an important bearing on the creation of a building. Similarly, in principle, a number of aspects of human memory could be importantly influenced by physiological or biochemical findings. However, many of the claims for an understanding of the molecular basis of memory that were being made a few years ago have since been shown to be premature—the neurochemistry of memory is proving much more complex than was previously suspected. There is no doubt that progress is being made in this important area, and that one day there may be a very fruitful collaboration between the human experimental psychologist and the neurochemist. At present, however, there is little area of overlap, so I will give only a brief account of some of the work concerned with the neurophysiology of learning and memory.

The neurophysiology of learning and memory

Learning almost certainly involves a chain of electrophysiological and neurochemical changes in the brain. Such changes are currently very difficult to study in the human brain, but considerable progress is being made in understanding the processes involved in learning in less complex organisms. For example, Eric Kandel has worked on the very simple marine organism Aplysia, which combines neuronal simplicity with a capacity for simple learning (Bailey & Kandel, 1995). It is capable, for example, of showing the phenomenon known as habituation. This is a process whereby a stimulus that initially evokes a response gradually comes to be ignored when it is repeated, in the absence of any positive or negative outcome. In the case of Aplysia, if one stimulates the siphon, both the siphon and the gill tend to be withdrawn initially; after repeated stimulation the withdrawal response stops, an effect that can last from minutes up to weeks. The withdrawal response involves electrical transmission across synapses, the special junctions between neurons, or nerve cells. Transmission across synapses depends on neurotransmitters, chemical messengers that allow one neuron to communicate with another. These in turn depend on the release of calcium ions. The process of repeated stimulation gradually reduces the activity of the channels that release calcium ions, thus reducing the likelihood that sufficient calcium ions will be released to cause firing or onward transmission of a nerve impulse.

The opposite to habituation is sensitization, a process that occurs when an independent stimulus increases the probability of a response. Hearing a shot, for example, might make you sufficiently jumpy to be startled by the sound of a car door slamming subsequently. In the case of Aplysia, an unpleasant stimulus to the tail enhances the withdrawal response when the siphon is touched. This is caused by an increase in the amount of neurotransmitter substance released as a result of a greater influx of calcium ions into the terminal.

Aplysia is also capable of the form of learning known as classical conditioning. The best known example of classical conditioning is that previously observed in dogs by the Russian physiologist Pavlov, who showed that when the presentation of food was regularly associated with ringing a bell, eventually the sound of the bell alone led to salivation. In the case of Aplysia, the equivalent to food is a strong stimulation to the tail, which causes the automatic response of withdrawing the gill and siphon. The equivalent of the bell is a mild touch of the siphon, which does not of itself lead to withdrawal. However, when the light touch is consistently followed by a strong tail stimulus, it eventually leads to withdrawal of the gill and siphon in the absence of the tail stimulus. This simple analogue of learning can persist for several days. Kandel suggests that the underlying mechanism is similar to that of sensitisation; the light touch to the siphon eventually leads, through association with the stronger tail stimulus, to an increase in the flow of calcium ions into the terminal, leading to firing and transmission of the nerve impulse across the synapse.

The underlying mechanism for more complex aspects of learning and memory remains in doubt. However, one possible mechanism is suggested by the effect known as long-term potentiation (LTP), a phenomenon first discovered by Bliss and Lomo (1973). While working on the hippocampus of the rabbit (a part of the brain that appears to be heavily involved in learning and memory), they found that intense electrical stimulation of connected areas resulted in hippocampal cells responding more strongly to stimuli than they had done previously. This enhanced response lasted for days, weeks, and even longer, suggesting that it might be a mechanism for long-term learning.

Subsequent research has indicated that LTP depends on the activity of the receptors on both sides of the synapse. When the presynaptic sending mechanism receives high-frequency stimulation, it releases the neurotransmitter glutamate. For LTP to occur, however, the post-synaptic or receiving neuron must also be operating at the appropriate level. The relevant post-synaptic receptors are sensitive to a substance known by the abbreviation NMDA (N-Methyl-D-Aspartate), and firing depends on having exactly the right balance of ions in the receptor channel. When both pre- and post-synaptic circumstances are right, the nature of the synapse changes, so that in future a much weaker pre-synaptic stimulus will cause the post-synaptic neuron to fire.

The fact that the cells associated with LTP are particularly numerous in the hippocampus, which is assumed to be crucially involved in learning and memory, provides some encouragement for believing that this may indeed be a basic learning mechanism. In a classic book published in 1949 the Canadian psychologist Donald Hebb speculated that a mechanism such as this might underlie the process

The Canadian psychologist Donald Hebb whose ideas, first proposed in the 1940s, are still highly influential. (Photograph courtesy University of Cambridge, Department of Experimental Psychology)

of learning. Since that time a number of computer-based learning models have been developed using Hebb's ideas.

How psychologists study memory

Although some psychologists are involved in trying to understand the physiological basis of memory, this approach will play little part in the remainder of the present account of human memory. If psychologists do not study memory by examining its physical or biochemical characteristics, how do they arrive at their findings? Do they simply ask people how they remember things? On the whole they do not. Although it is unwise to ignore people's comments on how they learn or remember, experience has shown that this kind of information is an unreliable source of evidence.

Consider, for example, the question of visual imagery. In the nineteenth century Sir Francis Galton did a classic study which involved writing to a large number of eminent men and asking them to try to conjure up an image of their breakfast tables on the morning they received this unusual request (Galton, 1883). They were asked to comment at length on the richness, detail, and vividness of the image they created, and enormously wide differences were observed, some respondents reporting that their remembered breakfast table was almost as vivid as their direct perception of it, others reporting no imagery at all. Subsequent work has confirmed that people differ extremely in the reported vividness of their imagery....