Table Of ContentCONTRIBUTORS
BERNARD W. AGRANOFF
E. J. CAPALDI
RONALD G. DAWSON
HENRY GLEITMAN
JAMES L. MCGAUGH
SAM REVUSKY
NORMAN E. SPEAR
EUGENE WINOGRAD
ANIMAL MEMORY
Edited by Werner Ę. Honig and P. Ç. R. James
Department of Psychology
Dalhousie University
Halifax, Nova Scotia
A C A D E M IC PRESS New York and London 1971
COPYRIGHT © 1971, BY ACADEMIC PRESS, INC.
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LIST OF CONTRIBUTORS
Numbers in parentheses indicate the pages on which the authors' contributions begin.
BERNARD W. AGRANOFF (243), Mental Health Research Institute and Depart
ment of Biological Chemistry, University of Michigan, Ann Arbor, Michigan
E. J. CAPALDI (111), Department of Psychology, Purdue University, Lafayette,
Indiana
RONALD G. DAWSON (215), Department of Psychobiology, School of Bio
logical Sciences, University of Cahfornia, Irvine, California
HENRY GLEITMAN (l). Department of Psychology, University of Pennsylvania,
Philadelphia, Pennsylvania
JAMES L. MCGAUGH (215), Department of Psychobiology, School of Biological
Sciences, University of California, Irvine, California
SAM REVUSKY* (155), Department of Psychology, Northem Dlinois University,
DeKalb, Illinois
NORMAN E. SPEAR (45), Department of Psychology, Rutgers University, New
Brunswick, New Jersey
EUGENE WINOGRAD (259), Department of Psychology, Emory University,
Atlanta, Georgia
* Present address: Department of Psychology, Memorial University of Newfoundland,
St. John's, Newfoundland, Canada.
IX
PREFACE
After a long period of neglect, experimental and theoretical work in the area
of animal memory has recently revived. The reasons for the neglect may be
historical, since the first systematic experimental work on forgetting was carried
out with (and by) a human subject, Hermann Ebbinghaus. They may be due to a
concentration of effort on acquisition processes in animal learning rather than
forgetting. Finally, the neglect may be due to the fact that "memory" is often
reified as a psychological entity which would be more easily examined through
human verbal report rather than animal behavior. But the advantages of using
animal subjects to study forgetting and retention are obvious. It is much easier
to control the extraexperimental sources of interference in animals than in
humans, both before and after the behavior of interest is initially acquired.
Animals can be held for long retention intervals which would normally involve a
considerable loss within a sample of human subjects. Such physiological
treatments as electroconvulsive shock and the administration of drugs that affect
the brain can be carried out on animals after acquisition. Finally, there is no
reason to believe that processes of retention, recall, and forgetting are any less
firmly based on empirical observation than the process of acquisition.
These observations are clearly illustrated in this survey of current work in the
area of animal memory. Since the contents of the book are based on a
symposium, coverage is selective rather than comprehensive. However, each
chapter provides a broad coverage of the topic with which it is concerned, and
the experimental work reported here is certainly representative of the most
significant developments in the field.
Two chapters are concerned with what we may call "associative
memory"-the memory of one event which is essential to its associarion (over a
delay) with subsequent events. Capaldi shows clearly that animals can remember
events from one leaming trial to the next and that their behavior will be
determined largely by the sequences of trials with differing outcomes. The
bearing of these associative processes on phenomena such as the partial
reinforcement effect and alternation is clearly discussed. Revusky reports a great
xi
Xii PREFACE
deal of research on the association of flavors with toxicosis in a conditioning
paradigm, but with long delays between the conditioned and unconditioned
sthnuli. He presents a theory of association and forgetting which is based largely
on concepts of interference.
The chapters by Gleitman and by Spear examine the current situation with
respect to what we may caU "retentive memory"-i.e., the retention and
forgetting of learned behavior over time. Gleitman argues strongly that animals
do forget, and examines theories of forgetting, with special attention to
interference theories, which do not seem to adequately explain the
phenomenon. Spear also develops a theorerical position, supported by extensive
data on animal forgetting. Distinguishing between "lapses" and "losses," he
argues in favor of a retrieval theory of remembering. Much forgetting is to be
explained by the absence of critical sthnuli, or "cues," at the trnie of recah,
rather than a permanent loss from the memory "store."
The chapters by McGaugh and by Agranoff examine the physiological basis of
memory in terms of consolidation theory. Electroconvulsive shock and
biochemical mjections, administered at various times after initial acquisition,
indicate that a process of "consolidation," perhaps involving transfer from
short- to long-term memory, is subject to interference. The complex paradigms
required to support such a notion are reviewed, and theoretical models are
proposed by each author. FinaUy, Winograd provides a critical discussion based
on all of the foregoing material in which the topics covered m the book are
related in an informative and constructive way to current work on human
retention and forgetting.
This book is based on the proceedings of a symposium held at DaUiousie
University in the summer of 1969. The chapters have been revised and the
material has been brought up-to-date since that time. We are very grateful to the
Faculty of Graduate Studies uf Dalhousie University for generous financial
support which made the symposium possible. Our colleagues in the Psychology
Department participated in organizing and directing the symposium. Dr. and
Mrs. C. J. Brimer carried a particulariy heavy share of looking after practical
arrangements. Finally, we want to thank Miss Margaret Ross, who has done
extensive secretarial and editorial work on the preparation of the contributed
papers for pubhcation. Without her services at a thne when both editors were
absent from DaUiousie for long periods of time, the publication of this book
would barely have been possible.
WERNER K. HONIG
P. H. R. JAMES
Chapter I
FORGETTING OF LONG-TERM
MEMORIES IN ANIMALS'
Henry Gleitman
The past two decades have seen an enormous burgeoning of interest in the
field of memory. Much of the research has been undertaken in the hope of
getting at the physiological basis of the memory trace, and it is hardly surprising
that most of these investigations used animal subjects. At least thus far, much
of this effort has concentrated upon the early stages in the life of the memory
trace. The biological basis of trace formation, decay and consolidation of
short-term memory, disruptions of the consolidation process, transfer from the
short-term to the long-term store-these are some of the topics that by now
constitute a substantial portion of the research literature. But interestingly
enough, there has been no comparable concern with the later phase in the life of
the trace. Once formed, consolidated, and transferred to long-term storage, the
memory trace seemed to hold Uttle further interest (at least until fairly recently)
to investigators working at the animal level, despite the fact that forgetting of
long-term memories is such an obvious fact of our own human experience.
Of course, this is not to say that forgetting of long-term memories has not
been studied seriously. Quite the contrary. Research on human forgetting dates
back to 1885 (Ebbinghaus, 1885) and ever since, the phenomenon has been a
primary concern of psychologists with a functionalist orientation (e.g.,
McGeoch, 1942) who have dealt with it in innumerable investigations of human
rote learning. But for the interpretation of their data, oddly enough, they often
turned to a realm quite different from that which had supplied the data they
wanted to interpret. The data (both for forgetting and for what were thought to
be the allied effects of retroactive and proactive interference) stemmed almost
exclusively from studies of human verbal and motor learning. On the other hand,
the inferred mechanisms offered as explanations for these data were usually
* This research was supported by U.S. Public Health Service Research Grants M-4993 and
MH-10629.
2 HENRY GLEITMAN
derived from phenomena observed primarily at the level of conditioning and
animal learning. Thus Underwood and Postman (1960) explained forgetting as
response competition caused in large part by the spontaneous recovery of
inappropriate habits extinguished in the course of original learning. There was a
gap here, which was all the more obvious in view of the relative paucity of
research on animal forgetting. When one talks of bar-pressing and salivary
responses, terms like "extinction" and "spontaneous recovery" have a fairly
clear-cut meaning; but one may well argue that this meaning alters when these
terms are used to discuss what happens to consonant trigrams. Our own program
was an attempt to fill this gap.
What follows is an account of our work during the last 8 years and a
discussion of the relevant literature, directed at two problems: (1) What, if
anything, do animals forget? (2) Why do they forget? In particular, how do the
findings bear upon interference, stimulus-change, and decay as theories of
forgetting?
I. What-IfAnything-Is Forgotten?
Do animals forget? Until fairly recently, the literature provided only scattered
accounts. Most workers in the area have been so impressed by the fact that
learned patterns persist, that few have asked whether they persist in full. Thus
Skinner (1950) is often cited as having shown that pigeons can maintain an
operant response over several years; only rarely is it mentioned that retention
was far from perfect, with losses up to 75%. The notion that habits are
essentially permanent-if well protected from interference and stimulus-
change-was certainly widely held (e.g., Kimble, 1961, p. 281), but has never
really been supported by solid empirical evidence. The few early studies on
animal forgetting often lacked necessary controls for postcriterial drops,
warm-up decrement, drive-state, and distribution of practice, and were thus
quite inconclusive. Our first task then was clear enough. We had to perform a
series of experiments (with appropriate controls for the various possible
artifacts) to answer a simple question: What, if anything, do animals forget?
What is meant by forgetting? The term has so many connotations from the
common language that some self-conscious definition-hunting may be quite in
order. To us, forgetting refers to some kind of performance decrement that can
be attributed to the effect of a retention interval. In essence, we refer to the
difference between test performance immediately after training and test
performance after a longer retention interval. Many other questions arise
immediately that bear upon the explanation of forgetting but that should be
kept quite separate from its definition. Is forgetting permanent or is it
transitory, or is it perhaps sometimes one and sometimes the other? Does the
effect occur during storage or at retrieval? Is the retention loss due to "time as
1. FORGETTING OF LONG-TERM MEMORIES IN ANIMALS 3
such," or to a change in stimulating context, or to interference? All of these are
interesting and important questions the answers to which will be critical for an
ultimate understanding of what forgetting is all about. But as we will use it here,
the term "forgetting" refers simply to some performance decrement in a learned
activity which is a function of time. It is in this sense that we ask the question:
Do animals forget?
Except for one study on goldfish, all of the experiments here reported used
rats as subjects; in most of them the drive was hunger and the reward was food.
Some aspects of the procedure were the same for all studies that employed
food-motivated rats:
1. The Ss were male, pigmented adult rats, ranging in age from 100 to 180
days at the start of each experiment. They were always run on the same
deprivation schedule, deprived for about 23 hours and maintained at 85% of
their adjusted bodyweight. They were placed on this schedule soon after they
arrived in the laboratory and were maintained on it during training, during the
retention interval, and during test.
2. The retention interval of the experimental groups was usually in the range
of 30-60 days while that of the control group was always 24 hours. We chose a
24-hour control interval in preference to intervals that are shorter, since this
equates across groups for possible satiation effects, activity levels, and warm-up
decrements.
3. Insofar as at all possible, the overall stimulus situation remained the same
for training, retention interval, and test. The Ss lived in the same cages
throughout the experiment, remained in the same room and were cleaned and
handled at the same time of day. The number of animals in the experimental
room stayed roughly constant and considerable care was taken to ensure
equality of visual, auditory, and olfactory cues at every stage of an experiment.
4. The method employed during the test trials was usually relearning, with a
procedure identical to that used in acquisition. In this manner both "recall"
(performance on the first test trial) and "relearning" (performance on the trials
thereafter) could be assessed.
5. In a few of the studies a control group was run to guard against possible
confounding effects due to differences in age, length of stay in the laboratory,
and length of time on the deprivation schedule. This group was brought into the
laboratory and placed on the drive schedule at the same time as was the
experimental group. The normal control group and the experimental group
would always receive their original training at the same time, the control group
being tested one day after training and the experimental group m days
thereafter. The age-drive control, however, would receive its training m days
later than the other two groups; consequently, its test trials would occur on the
same days as those for the experimental groups. On test trials both groups would
therefore be equated for age, length of time on the deprivation schedule, and
4 HENRY GLEITMAN
length of time in the laboratory. As it turned out, the results for the age-drive
control groups were virtually identical to those obtained for the corresponding
normal controls. In consequence, we eventually abandoned the age-drive groups
as unnecessary.
We shall first turn to those of our studies which show that rats indeed forget
in many situations, and second to those which show that they do not forget
under all conditions.
A. CONDITIONS UNDER WHICH FORGETTING OCCURS
1. Forgetting of ''Excitatory " Response Tendencies-The Runway
We have repeatedly found that rats forget simple instrumental responses Uke
running in an alley. The results of a representative experiment are presented in
the left-hand panel of Fig. 1 (Gleitman & Steinman, 1963). Twenty .Ss were
·2η
-24
-I 1—I 1 1
I 2 3 4 5 6
Blocks of Two Trials
Fig. 1. The effect of retention interval and prior extinction on runway performance
( 1 day, - - - 64 days). Results are presented as difference scores in log seconds between
performance on test and on the last four trials of acquisition. The panel on the left gives
results for 5s without prior interference, that on the right for Ss who were extinguished
prior to reconditioning. (From Gleitman & Steinman, 1963.) [Copyright (1963) by the
American Psychological Association, and reproduced by permission.]
given 20 trials (4 trials per day for 5 consecutive days) on a 6-foot runway, and
tested either 1 day or 64 days after training. The control group was placed on
the deprivation schedule on the same day as the experimental group, but was
trained 64 days later, thus equalizing age and drive state on the test trials.
Performance was assessed by measuring the total time required to traverse the
runway. The results for 12 test trials (4 trials per day for 3 consecutive days) are
presented as difference scores from the .Ss' performance on the last four trials of
training. Performance was evidently a function of retention interval, an effect
present both on the first test trial ("recall") and on the 11 reinforced test trials
thereafter ("relearning").
