Memory and Amnesia

An Introduction

Alan J. Parkin

• Publisher: Psychology Press
• Year: 2013
• ISBN:
  9781135064365
• Edition: 1
• Topic: Psychology
• Subtopic: History & Theory in Psychology
• Index: Psychology

Memory and Amnesia provides a clear and comprehensive account of amnesia set in the context of our understanding of how normal memory operates. Part I provides the reader with an up-to-date survey of contemporary memory theories along with an account of the various methods for improving memory ability. Part II begins with an overview of memory assessment which incorporates all important new developments, and focuses on the nature and explanation of the amnesic syndrome.
A new chapter deals with the emerging field of memory disorders linked to frontal lobe dysfunction, related to which is an entirely new approach to the study of age-related memory loss. The account of dementia is extended and includes a discussion of comparisons between different forms of the illness. The chapters on transient amnesic states and on psychogenic states are fully updated (including discussion of the false memory debate), and the significant advances in memory remediation are discussed in the last chapter.

Part 1
The Nature of Memory

1
A Model of Memory

One response to the question ‘How does memory work?’ might be to look at the anatomy and physiology of the brain. After all, memory is located there, so our knowledge of brain function might be expected to provide the answer. The brain is composed of millions of neurones, whose basic structure is illustrated in figure 1.1. Communication between neurones occurs by the transmission of nerve impulses along the axon of one neurone to the dendrites of another. The point of communication between an axon and a dendrite is called a synapse. Essentially it consists of two membranes separated by a minute gap. The impulse is transmitted by means of a chemical substance known as a neurotransmitter, which is released from the pre-synaptic membrane and travels to the post-synaptic membrane, where it sets up a new impulse. The level of interconnection between neurones is enormous, with a fully developed neurone averaging over a thousand dendritic and a thousand axonal synapses. The neuronal network therefore provides an ideal basis for the complex processes of memory.

In recent years neuroscientists have made major advances towards an understanding of the nervous system, but they have not reached the point where they can provide answers to many questions psychologists ask about memory. Thus we may be able to identify certain brain structures and neurotransmitters as being implicated in memory; but this does not tell us how memory is organized, why one learning strategy is better than another or, most mysteriously of all, how the interactions between these neurones give rise to our conscious recollections. We know that the neural networks of the brain underlie these activities, but unless we have a theory about how they are organized, we are no better off than someone who knows nothing about electronics trying to understand the circuits of a television.

Because the workings of memory are not apparent from the physical structure of the brain, explanations of memory must be based on analogies with things we do understand. The earliest and perhaps most famous example of a description of memory by analogy comes from Plato, who asks us to:

Figure 1.1 Cross-section of brain tissue showing neutonal network.

Imagine … for the sake of argument that our minds contain a block of wax, which in this or that individual may be larger or smaller, and composed of wax that is comparatively pure or muddy, and harder in some, softer in others, and sometimes of just the right consistency … and say that whenever we wish to remember something we hear or conceive in our own minds, we hold this wax under the perceptions or ideas and imprint them on it as we might stamp the impression of a seal ring. Whatever is so imprinted we remember and know so long as the image remains; whatever is rubbed out or has not succeeded in leaving an impression we have forgotten and do not know. (Theaetetus, translated by Hamilton, 1961, p. 897)

By means of a simple analogy, Plato provides a basis for discussing the formation of memories, memory capacity, and individual differences in learning ability, and distinguishes between different explanations of forgetting. Another analogy appears later, when Plato describes memory as an ‘aviary’, in which pieces of knowledge are represented by ‘birds’ which have to be ‘hunted down’ if that knowledge is to be used. This argument extends the wax tablet analogy in two important ways. First, it conceives of memory as a space in which individual memories are stored at specific locations, and second, it makes a distinction between storing information and the active search processes required to retrieve it.

The origins of recent memory models can be traced back to William James (1842-1910). Although he relied entirely on introspection, James had many important ideas about memory and other psychological processes, and we will refer to him at a number of points. Like Plato, James used a spatial analogy to describe memory; he compared the act of remembering to the way we ‘rummage our house for a lost object’. However, James introduced another important distinction, noting that new experiences do not disappear immediately from consciousness, but linger in awareness for a short period of time. He termed this phenomenon primary memory, and suggested that its contents did not need to be retrieved; hence ‘an object of primary memory is not … brought back; it was never lost; its date was never cut off in consciousness from that of the immediately present moment … it comes to us as belonging to the rearward portion of the present space of time, and not to the genuine past’ (James, 1890, pp. 646-7).

In James’s system the contents of primary memory pass into secondary memory, a large repository within which all our acquired knowledge is permanently stored. Information in secondary memory, unlike that in primary memory, has to be retrieved before it can be used. Unfortunately, James’s important insights into memory were ignored for more than half the twentieth century. This was largely attributable to the pervasive influence of behaviourism on the course of experimental psychology at this time. The behaviourists viewed any explanation which embodied consciousness as a concept unworthy of scientific interest; thus James’s dichotomy, with its emphasis on the relationship between consciousness and remembering, failed to attract any experimental investigation.

The ‘Multistore’ Model of Memory

Analogies used to explain memory are now referred to as models. These models still conceive of memory in spatial terms, but they tend to compare the organization of memory with that of a computer. Figure 1.2 shows a typical example of this approach. Memory is seen as a series of ‘stores’, each representing a different stage in the processing of information. New information first enters a sensory store, a form of memory whose existence has been confirmed only by means of modern experimental techniques. New information enters the nervous system via one or more of

Figure 1.2 The ‘multistore’ model of memory.
(After Atkinson and Shiffrin, 1968.)

our senses. Experiments have shown that the pattern of stimulation set up remains for a short period after the stimulus itself has been terminated. For visual information this form of sensory storage is known as iconic memory, and its existence was elegantly demonstrated by Sperling in 1960. In his experiment, subjects were shown three rows of letters, such as TDR, SRN and FZR, for only 50 milliseconds. When the subjects were asked to name all the letters, they could report no more than four or five. Alternatively, subjects were shown the array, and immediately afterwards were given a signal indicating which of the three rows should be reported; they then named all three letters correctly on most trials. Since the subjects had no advance warning as to which row they would be asked to report, they must have had the whole array available when the signal was given, even though the stimulus itself was no longer present. Sperling examined the time course of this partial report advantage, and found that it could be obtained only with intervals of less than a second between terminating the stimulus and giving the report signal, thus confirming that iconic memory is extremely transient. Sensory storage in other modalities has also been investigated, but discussion of this topic goes beyond our present concern.

During the period of sensory storage, information undergoes basic processes of identification before it passes into short-term store (STS). This store is conceptually equivalent to James’s primary memory, and provides the basis for our conscious mental activity. STS is the locus of control within the memory system; it determines what information is attended to and how information is processed, and governs retrieval of existing memory. STS can hold only a certain amount of information, and we refer to this capacity as our ‘span of awareness’ or, more typically, our memory span. Measurement of memory span is most commonly undertaken using the digit span technique. This measures the number of randomly arranged digits that an individual can repeat back in the correct order immediately after hearing or seeing them. In normal adults, digit span is around seven (plus or minus two).

The need for an STS is evident from consideration of a number of different tasks. When reading, for example, the earlier parts of a sentence must be kept in mind for the sentence as a whole to be understood. In performing a mental calculation, the outcome of one stage may need to be held while the solution to another stage is derived. Anecdotal evidence suggests that information in STS is vulnerable, and can easily be lost if some distraction or aversive event occurs. The everyday experience of being distracted and then being unable to remember what you were just saying is one example, as is the inability of concussion victims to remember events immediately preceding their accident.

Once in STS, information can have one of two fates: it can be transferred to long-term store (LTS), a structure of large capacity analogous to James’s secondary memory, or it can be forgotten. How transfer occurs will be considered a little later. For now it is sufficient to note that effective transfer of information to LTS involves the formation of a permanent memory trace, which subsequently provides the basis for restoring that information to consciousness. In figure 1.2 you will notice that there is an arrow going directly from LTS to sensory store. This acknowledges that LTS is needed for the identification processes carried out. These early processes are extremely complex in themselves, and include word identification and object recognition. Thus, by the time information reaches STS, a considerable degree of processing has been achieved. We are not aware of these initial processes, however; what passes into consciousness and hence into STS is just their end result. This relationship implies that only information that has been consciously perceived passes from STS to LTS. In general we will assume this to be the case, but allow for the possibility of remembering some things we are not aware of (e.g. see Eich, 1984).

Evidence for the STS/LTS Distinction

The distinction between STS and LTS is one that has strong intuitive appeal, but it is important to show that these hypothetical stores are separable components within the memory system. We will see later that evidence from amnesic patients bears on this issue; but for now, only experiments on normal memory will be considered. A number of techniques have been used; but we will concentrate on the free recall paradigm. This involves the sequential presentation of a series of items, usually words,

Figure 1.3 Typical finding from a free recall experiment, showing the three components of the serial position curve.
(After Glanzer and Cunitz, 1966.)

followed by the instruction to recall as many of the items as possible in any order.

The results are displayed by plotting the probability of an item being recalled as a function of its position in the list; figure 1.3 shows the resulting serial position curve. The first few items are remembered quite well relative to the items in the middle of the list; this is called the primacy effect. The best recall is obtained for the last few items in the list; this is termed the recency effect. The middle portion of the curve, where recall is poorest, is known as the asymptote.

Psychologists were quick to explain this result in terms of the STS/LTS distinction; the recency effect was interpreted as the output of STS, while recall from earlier in the list was thought to come from LTS. However, before this interpretation could be accepted, additional experimental evidence was required. If the serial position curve represented the joint operation of STS and LTS, it was necessary to show that the two parts of the curve responded differently when certain factors were manipulated. If one could isolate a factor which influenced recall from earlier parts of the list but had no influence on the recency effect and, by contrast, a factor which affected only the size of the recency effect, this would be consistent with the operation of two memory stores with different characteristics.

Subsequent experiments explored the serial position curve under a number of different conditions. Figure 1.4a shows that longer presentation time improves recall from early list positions but has no influence on recall of the last few items. A number of other factors were shown to have similar effects. Thus, recall from the primacy and asymptote portions of the curve was greater with word lists comprising of related items or more common words than with lists of uncommon or unrelated words. The only factor found to have the opposite effect was distraction prior to recall. This was shown by comparing the recall of subjects allowed to start remembering immediately after the last item had appeared with that when they were required to count backwards in threes for 30 seconds before recalling the items. Under these conditions, the recency effect was completely eliminated, without any change in recall from the other parts of the list (see figure 1.4b).

These results are most readily interpreted by assuming that recall from different parts of the list reflects the output of different memory stores. The ease with which the last few items are recalled and the susceptibility of this effect to distraction support the existence of an STS from which new information is immediately available, but which is vulnerable to disruption. Conversely, the fact that distraction does not affect recall from earlier in the list indicates that this information has achieved permanent storage in LTS. The identification of factors which influence recall from this part of the list but fail to influence the recency effect also supports the multistore interpretation of the serial position curve. Furthermore, the variables influencing recall indicate factors that are pertinent to the operation of LTS itself. For example, the finding of enhanced recall when items are meaningfully related confirms what we might expect: that memory is more effective for organized material.

If we conceive of memory formation as the transfer of information from STS to LTS, we must consider what factors might influence this process. The most obvious of these is that the brain itself should be working normally, and the consequences of brain malfunction on memory constitute a major part of this book. However, normal individuals often fail to remember things, and, under certain circumstances, this could be attributed to an ineffective transfer from STS to LTS. Proponents of the multistore model have suggested that successful transfer may depend on the amount of rehearsal the information receives. This concept stems from our natural tendency to repeat new information, either aloud or silently, in an effort to remember it. The relationship between rehearsal and memory was demonstrated by Rundus in 1971, using a modified version of the free recall technique. Subjects were presented with a list of words, and w...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Preface to the First Edition
• Preface to the Second Edition
• Acknowledgements
• Part 1 The Nature of Memory
• Part 2 Memory Disorders
• Suggestions for Further Reading
• References
• Name Index
• Subject Index