Forgetting

Sergio Della Sala

• Publisher: Taylor & Francis
• Year: 2010
• eBook ISBN: 9781136970863
• Edition: 1
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

Memory and forgetting are inextricably intertwined. In order to understand how memory works we need to understand how and why we forget. The topic of forgetting is therefore hugely important, despite the fact that it has often been neglected in comparison with other features of memory.

This volume addresses various aspects of forgetting, drawing from several disciplines, including experimental and cognitive psychology, cognitive and clinical neuropsychology, behavioural neuroscience, neuroimaging, clinical neurology, and computational modeling. The first chapters of the book discuss the history of forgetting, its theories and accounts, the difference between short-term and long-term forgetting as well as the relevance of forgetting within each of the numerous components of memory taxonomy. The central part summarizes and discusses what we have learned about forgetting from animal work, from computational modeling, and from neuroimaging. Further chapters discuss pathological forgetting in patients with amnesia and epilepsy, as well as psychogenic forgetting. The book concludes by focusing on the difference between forgetting of autobiographical memories versus collective memory forgetting.

This book is the first to address the issue of forgetting from an interdisciplinary point of view, but with a particular emphasis on psychology. The book is scientific and yet accessible in tone, and as such is suitable for advanced undergraduate and postgraduate students of psychology and related subjects, such as science and neuroscience.

1
Forgetting

Preliminary considerations

Henry L. Roediger III, Yana Weinstein, and Pooja K. Agarwal
Washington University in St. Louis, USA

The existence of forgetting has never been proved: we only know that some things do not come to our mind when we want them to.

(Friedrich Nietzsche, 1844–1900)

Of all the common afflictions from which humankind suffers, forgetting is probably the most common. Each of us, every day, forgets something we wish we could remember. It might be something we have done, something we intended to do, a fact, a name of a person or restaurant, and so on ad infinitum. As we age, our incidents of forgetting increase and we worry more about them. A whole industry of books, tapes, and even new mental gymnasia has grown up to deal with the cognitive frailties of old age, the primary one being rampant forgetting. Compared to other nuisances of life, forgetting probably tops the list. The “common cold” is actually quite rare compared to forgetting in all its manifestations. As Underwood (1966) wrote: “Forgetting is a most exasperating and sometimes even painful phenomenon” (p. 542). More recently, Nairne and Pandeirada (2008) maintained that for most people “forgetting is a scourge, a nuisance, a breakdown in an otherwise efficient mental capacity” (p. 179), although they quickly noted that there is often an adaptive value in forgetting too.

Despite the fact that psychologists have been studying learning and memory for 125 years, the current volume is the only one we can find devoted solely to the topic of forgetting. “Forgetting” is a term used in the titles of many works of fiction and even cultural critique (see Markowitsch & Brand, Chapter 2), but this volume is the first scientific one devoted to it. Strange, you might think.

Given the ubiquity of forgetting in our daily lives, the quote by Nietzsche that heads our chapter must seem stranger still. Given its ubiquity, how can the existence of forgetting be doubted? Difficulties of these sorts usually revolve around matters of definition, and that is the case here. We turn to this issuefirst.

Defining forgetting

According to the authors of the International encyclopedia of the social sciences: “It seems quite unnecessary to be concerned with a definition of ‘forgetting’ ” (Sills & Merton, 1968, p. 536). Nonetheless, psychologists have attempted to define forgetting in several different ways. Cubelli (Chapter 3) provides a thorough exploration of the various extant definitions of forgetting, and below we give a general overview. Before undertaking the task of examining these issues, however, we review some preliminary considerations. At least since Köhler (1947, p. 279), psychologists have found it useful to distinguish among three stages in the learning/memory process: acquisition (encoding), storage (maintenance or persistence), and retrieval (utilization of stored information, see too Melton, 1963; Weiner, 1966). Encoding or acquisition is the initial process in learning, although this process may be extended in time as a memory trace (a persisting representation) formed through consolidation. Only events that have been securely encoded or learned in the first place can be said to be forgotten; it makes no sense to say that one has forgotten the 15th name in the Auckland, NZ, telephone book or the capital of Mars, because one never knew these bits of information in the first place. We take Tulving’s definition of forgetting – “the inability to recall something now that could be recalled on an earlier occasion” (1974, p. 74) – as our starting point in considering more complex definitions. We consider first the strongest form of the concept of forgetting, the one implicit in the quote from Nietzsche.

Forgetting as complete loss from storage

Davis (2008) defines the strong form of forgetting as “the theoretical possibility that refers to a total erasure of the original memory that cannot be recalled, no matter what techniques are used to aid recall” (p. 317). Given the context of his chapter, we feel sure he would be willing to include not just measures of recall, but any measure (explicit or implicit, direct or indirect) of the prior experience having been encoded in the nervous system. Davis argued that it would only be possible to look for “strong” forgetting in simple organisms (e.g., simple gastropods like slugs) where the entire neural circuitry has been mapped out. “Only when all the cellular and molecular events that occur when a memory is formed return to their original state would I say this would be evidence for true forgetting” (Davis, 2008, p. 317).

To our knowledge, no evidence for this strong form of forgetting has been produced even in simpler organisms; and since all the research in the present volume is about forgetting in organisms more complex than mollusks, it would be practically impossible to obtain evidence for this strong form of forgetting. Even if every test known to psychologists failed to show evidence for any sort of trace of past experience, the possibility remains that a change owing to that prior experience (some latent memory trace) still remains.

Davis (2008) concluded that the strong form of forgetting is not scientifically useful, and we agree with him. We can ask the further question: If the strong form of forgetting can never be proved (as Nietzche’s dictum states), does this mean that forgetting in this sense never occurs? We think the answer to this question must be no (although we cannot prove it). Think of all the events and happenings that occurred to you when you were 7 years old, ones you could have easily reported the next day (so they were encoded). Do you still really have traces of all these events lying dormant in your brain, waiting for the right cue to become active again? We strongly doubt it. Probably the many of the millions of events, conversations, facts, people, and so on that are encountered in everyday life and at one point committed to memory do suffer the strong form of forgetting by being obliterated from our nervous systems. However, that is a matter of faith, given that we cannot find proof. As we discuss below, it is possible to entertain a contrary possibility, because powerful cues can bring “forgotten” information back into consciousness. Still, given the huge number of events in one’s life, the idea that all would be stored forever (in some form) seems unlikely.

Forgetting as retrieval failure

Another possibility, essentially the obverse of the strong form of forgetting, might be considered a weak form of the concept. In its starkest form, this idea would maintain that all events that have been encoded and stored do somehow persist in the nervous system (including all those from age 7), and the inability to access them now is due to retrieval failure. Although this proposal might seem farfetched, when Loftus and Loftus (1980) surveyed psychologists many years ago, a large percentage (84%) favored something like this view. The percentage today might be lower, but the 1970s were the heyday of studies of retrieval in general and the power of retrieval cues in particular (Tulving & Thomson, 1973; for reviews see Roediger & Guynn, 1996; Tulving, 1983).

The idea of forgetting as retrieval failure is a scientifically useful concept, because (unlike the case with forgetting as storage failure) evidence can be found in its favor. Let us consider one experiment to demonstrate the point. Tulving and Pearlstone (1966) presented high-school students with lists of words to remember. Although there were many conditions, for our purposes consider the condition in which students studied 48 words that were members of 24 common categories, so they heard two words per category. Thus, students heard lists such as “articles of clothing: blouse, sweater; types of birds: blue jay, parakeet.” The words were presented at a slow rate (2.5 sec/word) so the encoding of the words was ensured, in the sense that if the experimenter had stopped at any point, the subjects could have successfully recalled the last word presented. Thus, in this sense, all 48 words were learned.

One group of subjects was tested by free recall; they were given a blank sheet of paper and asked to recall the words in any order. They recalled 19.3 words, which means they forgot (failed to retrieve) about 29 others (28.7 to be exact). We can thus ask what happened to the forgotten words. It is logically possible that their representations had completely evaporated and had vanished from storage, but, as already discussed, we can never assume that. On the other hand, it could be that traces of the words were stored, but could not be retrieved with the minimal cues of free recall (people must use whatever cues they can internally generate). Tulving and Pearlstone (1966) found evidence for this latter possibility by giving the students (both the same group that had received a free recall test and a different group that had not had such a test) category names as cues. When the 24 category names (e.g., articles of clothing) were given, students were able to recall 35.9 words (and it did not matter much as to whether or not they had taken the prior free recall test). Thus, with stronger cues, students were able to recall nearly twice as many words as in free recall, showing that some of the forgetting in free recall was due to retrieval failures. Such powerful reversals of forgetting demonstrated in many experiments were probably why the psychologists surveyed in the late 1970s by the Loftuses claimed that forgetting was mostly due to retrieval failures.

Of course, even with the powerful category name cues, students still forgot about 25% of the words (12 of 48). Were these lost from storage? There is no way to know, but probably if the students had been further probed with recognition tests (with strong “copy cues”) or with implicit tests (Schacter, 1987), evidence for storage of even more words would have been found. The asymmetry in the logic here – evidence of forgetting as retrieval failure can be obtained, but evidence of forgetting as storage failure cannot – leads back to Nietzsche’s dictum. Still, as noted above, we cannot conclude that forgetting never involves elimination of stored traces, just that such a claim cannot be verified scientifically.

Forgetting as loss of information over time

A third way of defining forgetting, the one first used since Ebbinghaus (1885/1964) and many others since his time, is to plot retention of some experiences over time. This definition is complementary to the forgetting-as-retrieval-failure definition, not opposed to it. The typical way to conduct such forgetting experiments is to have (say) seven groups of subjects exposed to the same information (e.g., a list of words). One group would be tested immediately after learning, with other groups tested at varying delays after that point (e.g., 1 hour, 6 hours, 12, hours, 24 hours, 48 hours, and 1 week). Retention would be plotted across the various retention intervals and a forgetting curve would be derived, almost always showing less information recalled or recognized as a function of the time since learning. As Ebbinghaus (1885/1964) put it: “Left to itself every mental content gradually loses its capacity for being revived, or at least suffers loss in this regard under the influence of time” (p. 4). One critical methodological stricture in such experiments is that the type of test be held constant across delays, so that retrieval cues do not differ.

As noted, Ebbinghaus (1885/1964) was the first to plot forgetting over time. He presented his results in a series of tables in his book (see pp. 67–76), but later writers have chosen to show them...

Table of contents

• Current Issues in Memory
• Contents
• Contributors
• Preface
• 1 Forgetting
• 2 Forgetting
• 3 A new taxonomy of memory and forgetting
• 4 Forgetting in memory models
• 5 Connectionist models of forgetting
• 6 Synaptic plasticity and the neurobiology of memory and forgetting
• 7 The functional neuroimaging of forgetting
• 8 Sleep and forgetting
• 9 Forgetting due to retroactive interference in amnesia
• 10 Accelerated long-term forgetting
• 11 Aspects of forgetting in psychogenic amnesia
• 12 Autobiographical forgetting, social forgetting, and situated forgetting
• 13 The role of retroactive interference and consolidation in everyday forgetting
• Author index
• Subject index