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This is to certify that the

thesis entitled
The Effects of Cue Delay on
Directed Forgetting in the Pigeon

presented by

Thomas Branch Stonebraker

has been accepted towards fulfillment
of the requirements for

J degree in 1mm“:

 

   
 

Major professor

MWO

0-7639

THE EFFECTS OF CUE DELAY ON

DIRECTED FORGETTING IN THE PIGEON

BY

Thomas Branch Stonebraker

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF ARTS

Department of Psychology

1980

ABSTRACT

THE EFFECTS OF CUE DELAY ON
DIRECTED FORGETTING IN THE PIGEON

BY

Thomas Branch Stonebraker

A successive delayed matching-to—sample procedure was modified
to determine if stimulus control of rehearsal processes could
be obtained. Procedures were modeled after the directed
forgetting procedures commonly used in human memory studies.
Cues during the interstimulus interval signalled the occur-
rence (remember cues) or nonoccurrence (forget cues) of com-
parison stimuli. Memory strength remained constant on re-
member cued trials regardless of the temporal location of

the cue within the interval. Evidence indicates that re-
hearsal processes were terminated on trials in which the for-
get cue was given. Consequently, memory strength varied as

a function of cue location on those trials, with early cues
leading to poorer matching performances than late cues. A
control condition established that the important variable in-
volved in the effectiveness of a forget one was the interval
between the forget cue and the comparison stimulus. Results
demonstrate stimulus control over an active rehearsal process

in the pigeon.

To My Wife, Regina, Whose
Love And Support Has Been
Essential In The Completion

Of This Thesis

ii

ACKNOWLEDGEMENTS

I would like to thank Dr. Mark Rilling for his guidance
and supervision of this thesis. Dr. M. Ray Denny, Dr. Gordon
Wood, Daniel K. Tranberg, and Donald F. Kendrick also provided
valuable comments and suggestions throughout the development

of this research.

iii

LIST OF TABLES. . .

LIST OF FIGURES . .

INTRODUCTION. . . .

METHOD 0 O O O O O 0

RESULTS 0 O O O O 0

DISCUSSION. . . . .

LIST OF REFERENCES.

TABLE

OF CONTENTS

iv

vi

27
34
45

50

LIST OF TABLES

Table Page

 

1. Training procedures for Phase I and the
Transition Phase. . . . . . . . . . . . . . . . 29

2. Training and testing procedures for Phases II,
III, IV, and V. O O O O O I O O O O O O O O O O 32

3. Response per minute during comparison stimuli
following Remember (R) and Forget (F) cues
during 4 and 2.5 second retention intervals
‘with various cue delays. Trial types are
red-red (RR), green-green (GG), red-green (RG),
and green‘red (GR). . . . . . . . . . . . . . . 35

LIST OF FIGURES

Figure

1. Matching performance as a function of cue delay
on remember (R) and forget (F) cued trials.

2. Mean keypecks during 4 second retention intervals
as a function of one delay and remember (R) and
forget (F) cues.

3. Comparison of matching performance on Phase V
(control condition) to Phases III and IV.

vi

40

42

INTRODUCTION

The 1960's saw the advent of a new approach to human
processes, formally born with the publication of Ulric Neisser's

Cognitive Psychology (1967). After 50 years or so of suppression

 

through the prevalence of behaviorism, researchers once again
began to ask questions about the higher mental processes studied
by the structuralists. At the heart of this new perspective
was the assumption that human beings are active, information
seeking and using organisms contrary to the mechanistic view
of the radical behaviorists regarding human beings as passive
accumulations of associations (see Reynolds and Flagg, 1977,
Chapter 1). Cognitive psychology used the methods perfected
by the neo-behaviorists, along with concepts and techniques
borrowed from the new fields of linguistics, computer science
and information theory, to study the mental structures and
processes of attention, language perception, learning and
memory.

Work on the nature of memory processes has been one of the
focuses of the cognitive movement. One particular concept that
has been useful in this research is the distinction between
short- term and long—term memory. Short-term memory (STM) is
considered to be of limited capacity and short duration (in-
formation is quickly lost if not actively rehearsed) while
long-term memory (LTM) is of a more permanent nature. Despite

1

2
the fact that there is not universal acceptance of STM and LTM
as a conceptual distinction, few would argue its usefulness
as an operational distinction. Dividing memory into short-term
and long-term processing components has been a useful tool in
describing and explaining many aspects of memory processing.
The idea of a two component memory system in humans is an old
one. Psychologists as early as William James have made a dis-
tinction between "primary and secondary memory" (James, 1890).
Physiological evidence such as Milner's syndrome (where victims
of neural damage are unable to remember events in the recent
past, but can remember events in the remote past) also seemed
to indicate separate memory processes of short and long duration.
It was not until the late 1950's, however, that there was any
widely recognized empirical support for a two component memory
system. This evidence came with the develOpment of a new tech-
nique by Brown (1958) and by Peterson & Peterson (1959) that
demonstrated rapid forgetting in humans. The Brown-Peterson
technique consisted of presenting a single verbal item for re-
tention, employing a distraction task to prevent rehearsal, and
testing retention after some variable length retention interval.
Peterson and Peterson found retention to decrease monotonically
with the length of the retention interval. They found that the
near perfect retention at three second retention intervals de-
creased steadily to very low retention (10%) at 18 second re-
tention intervals. No one prior to Brown and the Petersons
had thought to look for memory loss at such short retention
intervals--memory loss functions had typically been plotted in

terms of hours and days rather than seconds. This major advance

3
allowed the assessment of short-term memory and rapid for—
getting, opening the doors to diverse possibilities in memory
research.

Directed Forgetting

 

Within the realm of memory research an area that has been
extensively studied is directed forgetting. During the 1960's
the main focus in human memory research was on intentional
remembering and incidental forgetting. While this line of re-
search adequately dealt with a great deal in the area of memory
processes, there were still some aspects which were inaccessible.
Bjork, LaBerge and LeGrande (1968) developed the procedure of
directed forgetting in order to get at some of these unanswered
questions. Directed forgetting, with its focus on intentional
forgetting and incidental remembering, (Woodward & Bjork, 1971),
was the next step in the progression of human memory research.
As Bjork (1972) puts it, the primary concern of directed for—
getting research is to understand how current to-be-remembered
information is discriminated from past to-be-forgotten infor-
mation. Bjork points out how vital this updating process of
intentional forgetting is in everyday life. Realizing the
vast amount of information a human comes in contact with
during the course of a day, it would be both uneconomical and
counterproductive for a person to attempt to remember all of
the information that is attended to. Directed forgetting pro-
cedures provide an empirical situation that allows investiga-
tion of how these items are differentiated in memory.

In the basic directed forgetting procedure a subject is

given a set of items to memorize (usually words or trigrams).

4

Some of these items are followed by a remember (R) cue and
others are followed by a forget (F) cue. These cues either
follow a series of items (blocked cueing procedure) or each
individual item (item by item cueing procedure). The R cue
indicates that the subject will be required to remember the
to-be-remembered (TBR) items while the F cue indicates that the
subject does not need to remember the to-be-forgotten (TBF)
items. It is often pointed out to the subjects that remembering
the TBF items is counterproductive and that the best strategy
is to forget those items. Following the presentation of the
TBR and TBF items retention tests are given to access the
memory for those items. Subjects are tested for items that they
knew they were going to be tested on (TBR items) as well as
items they were misled to believe they would not be tested on
(TBF items) .

Using the directed forgetting technique within a modified
version of the Brown-Peterson procedure several researchers
have found that subjects are very capable of utilizing R and
F cues in their memorization processes. Recall of TBR items
is consistently better than recall of TBF items (Bjork, 1970;
Bjork, LaBerge & LeGrand, 1968, Block, 1971; Davis & Okada,
1971; Elmes, Adams & Roediger, 1970; Epstein, 1970; Woodward
& Bjork, 1971; Woodward, Bjork & Jongeward, 1973). According
to Jongeward, Woodward, and Bjork (1975) the primary effect
of cueing a portion of the items in a list as TBF items is a
drastic reduction in the retrievability of those items. Se-
condly, instructing subjects to forget some of the items reduced

the amount of interference of these TBF items (Bjork, et al.,

5
1968; Block, 1971) on TBR items. This reduced interference
leads to an enhanced retention of those TBR items. The com-
bination of a reduction in retrievability of TBF items and
reduced interference produces a very stable phenomenon in
the relative superiority of the retention of TBR items over
TBF items.

Explanations for the directed forgetting phenomenon usually
emphasize either input mechanisms or output mechanisms. Bjork
and his colleagues have focused primarily on the influence of
input mechanisms. Bjork (1972) proposed two mechanisms as the
controlling variables in directed forgetting: differential
rehearsal of TBR and TBF items and differential grouping of
these items to functionally separate them in memory. Bjork
believes that the superior retrievability of TBR items is due
to a combination of these two factors. Epstein and his col-
leagues focus on output rather than input mechanisms, and
have questioned the necessity of rehearsal in accounting for
the basic directed forgetting effect (Epstein, 1972; Epstein,
Massaro & Wilder, 1972; Shebilske, Wilder & Epstein, 1971).
These researchers rely solely on a selective search hypothesis
based on the partitioning of TBR and TBF items to account for
the effectiveness of the forget cue. Recent studies seem to
indicate that the weight of evidence favors the position of
Bjork (Jongeward et al., 1975; Wetzel, 1975; Wetzel & Hunt,
1977; Woodward, Park & Seebohm, 1974). These studies reconfirm
the important role of rehearsal and other processing mechanism
at input. These findings are contrary to Epstein's sole re-

liance on search and retrieval processes at output. Bjork

6
(1972) points out that selective rehearsal and differential
grouping are integrally related and that the two mechanisms
co-imply each other. "That is, efficient selective rehearsal
of R items as a set, and the differentiation of R items as a
set may depend on their being rehearsed together" (P. 229).
Rehearsal processes seem to be integrally related to the directed
forgetting effect and must therefore be accounted for in any
theoretical explanation of the phenomenon.

Levels of Processing

 

Craik and Lockhart (1973) draw an important distinction
between primary and secondary rehearsal, each of which is a
different class of rehearsal processes. While some researchers
have placed less emphasis on the levels of processing approach
(Baddeley, 1978) it still appears to be a useful framework for
a great deal of memory research. Primary (Woodward et al.,
1973), Type I (Craik & Lockhart; Glenberg & Adams, 1978) or
maintenance (Craik & Watkins, 1973) rehearsal is primarily
associated with STM, and is assumed to maintain information by
rote repetition. Waugh and Norman (1965) and Atkinson and
Shiffrin (1968) propose that rehearsal both maintains an item
in short-term store and simultaneously transfers at least part
of that information to long-term store. According to this
model the probability that an item will be encoded in long-term
memory is dependent on the amount of time it is held in short-
term memory (Meunier, Ritz, & Meunier, 1972). Other researchers
(Craik & Lockhart; Craik & Watkins; Jongeward, Woodward &
Bjork, 1975; Glanzer & Meinzer, 1967; Glenberg, Smith & Green,

1977; Tulving, 1966; Tulving & Colotla, 1970) have demonstrated

7
that maintaining information in short-term store does not
necessarily affect delayed recall performance. They found no
relationship between the two when the rehearsal process that
was used to maintain the information was of a rote maintenance
(as opposed to elaborative) nature.

In contrast to Type I rehearsal, Type II or secondary re-
hearsal is highly associated with delayed memory performance.
This "deeper" more elaborative type of processing leads to more
durable memory traces through the use of greater association
formation between TBR items (Woodward et al., 1973), or through
greater "processing effort" according to Craik and Lockhart's
concept of depths or levels of processing. In directed for-
getting studies using words or trigrams as TBR and TBF items,
this "depth" implies a greater degree of semantic or cognitive
analysis. Through Type II rehearsal the items being rehearsed
become actively associated with each other and with other in-
formation in long-term memory. Making a distinction between
two modes of rehearsal, Craik and Watkins state:

Time in short-term store will only predict later long-

term store performance when the subject has used the

time to encode the items elaborately. Contrary to the

models of Atkinson and Shiffrin (1968) and Waugh and

Norman (1965), time in short-term store does not by

itself lead to long-term retention. (P. 603)

Relationship Between Rehearsal Level and Directed Forgetting

 

In directed forgetting studies the effect of the amount
of processing on performance in recognition and recall tests
is highly dependent upon whether the rehearsal process being
varied is the Type I or Type II nature. For a typical recog-
nition task the subject is asked to identify words that had

previously been given from a large set of given words. When

8

recall is tested the subject is simply asked to give as many
items as he or she can remember. The presence of the exact
items as retrieval cues on a recognition test has lead many to
believe that only recall, and not recognition, requires a
retrieval process on the part of the subject (e.g., Underwood,
1972) Woodward et a1. (1973) have theorized that greater rote
maintenance rehearsal increases both recognition and recall.

A presupposition for the position held by Woodward et a1.
is the common sense notion that the memory of an item will vary
directly proportionally to the amount of rehearsal that has
been allowed for that particular item (this line of reasoning
is of course essential to Bjork's hypothesis on the role of
selective rehearsal in directed forgetting). Strangely, initial
studies failed to support even this simple relationship bet-
ween amount of rehearsal (rote or elaborative) on memory of
an item as tested by either recall or recognition tests. Davis
and Okada (1971), using an item by item cueing procedure,
attempted to manipulate the amount of rehearsal by using either
a delay or no delay between an item and the cue to forget.

Delay of cueing in the input list did not have any marked effect
on either recall or recognition of TBR or TBF words. One very
serious drawback in the design of the Davis and Okada study

was that they only used delays of 0 and 1 seconds. This range
was too minimal to examine any real effect the amount of re-
hearsal may have had on subsequent recall and recognition tests.

Woodward and Bjork (1971) also failed to demonstrate a re-
lationship between amount of rehearsal and later memory strength

using work presentations that were 1, 2, or 4 seconds before the

9

cue to remember or forget was given. A drawback in the design
of their study was that each word remained in view until the
cue appeared. It is very conceivable that in this situation
the amount of rehearsal was not varied at all. The subjects
in Woodward and Bjork's study could very easily have avoided
any active rehearsal of the work being presented until the cue
was given.

Contrary to the above findings (or perhaps more accurately
the lack of findings) were the findings of Glenberg, Smith and
Green (1977) and Meunier, Ritz and Meunier (1972) that there
was a direct relationship between rehearsal and retention. Al-
though not using directed forgetting procedures, these investi-
gators used a modified version of the Brown-Peterson procedure
to demonstrate a direct relationship between amount of Type I
rehearsal and recognition. A similar relationship was also
found between the rehearsal and performance on an immediate
(but not delayed) recall test.

Woodward et al. (1973) were dissatisfied with the counter-
intuititive inability of previous directed forgetting studies
to show this positive relationship between amount of rehearsal
and retention. They set out to eliminate the procedural as-
pects of the Davis and Okada and the Woodward and Bjork studies
which seemed to have confounded the results. Woodward et al.
used rehearsal periods of 0, 1, 2, 4, 8, and 12 seconds between
the offset of the word and the onset of the R or F cue, there-
by eliminating the two major flaws previously mentioned in
regards to the earlier studies. The various retention inter-

vals were randomly distributed throughout the list in an item

10
by item cueing procedure. They found that the duration of
rehearsal had a heavy influence on performance on a final
recognition test. However, they were also unable to find
any effect of differential amounts of rehearsal on final re-
call. Woodward et a1. suggested that the results they ob-
tained were a function of the type of rehearsal being utilized
by their subjects. They hypothesized that their procedure
made it inappropriate for subjects to rehearse each word in an
active, constructive way, since each word had an equal proba-
bility of being followed by a cue to simply forget that word.
Associative or integrative (Type II) rehearsal was, according
to this account, counterproductive prior to any R or F cue.
They therefore offered the explanation that subjects merely
engaged in rote nonassociative processing, which was conceived
of as independent of long term memory. Glenberg et a1. (1977),
Jongeward et al. (1975), and Rundus (1977) have shown that the
duration of this Type I rehearsal does not affect delayed re-
call. As previously stated, Glenberg and Adams (1978) demon-
strated that the duration of Type I rehearsal does, however,
affect the memory trace as measured on a recognition test. It
can then be seen that in Woodward et al's study the various
amounts of Type I rehearsal of each item produced the resultant
effect on recognition performance. Recall performance, on the
other hand, heavily depends on interassociations and interre-
lations between items in memory, as can be seen in Craik and
Watkin's (1973) hypothesis that only elaborative rehearsal
affects long-term memory. Woodward et al.'s explanation that

subjects only engaged in rote primary rehearsal would therefore

11
explain their inability to demonstrate any effect of amount
of rehearsal on recall performance.

Further studies by Wetzel (1975) and Wetzel and Hunt
(1977) established a direct relationship between amount of re-
hearsal and both recognition and recall by modifying the tech-
niques of Woodward et a1. These studies clearly demonstrated
that Woodward et al.'s failure to find an influence of amount
of rehearsal on final recall was not as much due to the lack
of Type II rehearsal as it was a function of the particular
cueing techniques used. Wetzel showed that Woodward et al.
failed to produce appreciable differences in recall due to
their within list variation of processing Opportunities. This
technique allowed subjects to rehease previously R cued items
during subsequent retention intervals. During any given reten-
tion interval subjects were able to time-share their rehearsal
of the present to-be-cued item and past TBR items. The net
effect was that this procedure equated the amount of processing
activity devoted to words that were initially followed by
different word-cue intervals (also see Bjork & Geiselman, 1978).
Wetzel remedied this situation by varying the amount of re-
hearsal as controlled by the word-cue delay between lists to
ensure a relatively uniform processing opportunity across each
list. Using this modified procedure Wetzel and Wetzel and
Hunt were able to demonstrate a direct relationship between
processing opportunities and performance on both recognition
and recall tests.

According to Bjork and Geiselman (1978) the superiority

of TBR word recall over TBF word recall in a final recall

12
test is a result of the fact that TBF words are only given
an initial amount of rote maintenance rehearsal proportional
to the word-cue interval. When a forget cue is presented pro-
cessing is terminated or inhibited. A remember cue directs
the subject to retrieve the word and engage in an elaborative
or secondary rehearsal during the remaining cue-word interval,
as well as on following trials. Wetzel's studies demonstrate
that varying the amount of this elaborative rehearsal results
in a directly related variation in final recall in a way quite
similar to the previously established relationship between
Type I rehearsal and recognition. These results clearly support
Woodward et al.'s theory that greater rote maintenance rehearsal
increases recognition performance while greater elaborative re-
hearsal increases both recall and recognition. More generally,
Wetzel's and Wetzel and Hunt's results confirm Bjork's hypoth-
esis that differential rehearsal Opportunities do contribute
to the superior retention of TBR items in the directed for-
getting pardigm. In contrasting Wetzel's work with the work
of earlier researchers who failed to show such a clear-cut
relationship between rehearsal and retention, it can be seen
that this effect is highly dependent upon the methods used.

Research on STM in Pigeons

 

Heavily influenced by research in human processing, re-
searchers in animal behavior have recently incorporated cog-
nitive procedures. Historically, psychologists have applied
the findings of animal research to human behavior, based on
the principle of biological continuity among species. Animal

studies replaced many human studies by virtue of the greater

13

experimental control attainable with subhuman subjects. How-
ever, movement on the phylogenetic continuum is not restricted
to merely one direction by the principle of biological con-
tinuity. Recent authors such as Honig (1978) and Fowler (1978)
have started exploring the benefits of applying the findings
of cognitive psychology in humans to the study of cognitive
processes in animals. A specific example of this trend that
is quite relevant to the topic at hand is the parallel between
Bjork's statements on the importance of forgetting in human
memory processing discussed earlier and Olton's (1978) statement
concerning rats, that "If there is limited working - memory
capacity, being able to forget is often as important as being
able to remember because the memory process will be more
effective the fewer items that are already in storage" (p. 352).

In addition to allowing for greater experimental control
and a broader range of possible manipulations, the use of
animals to study cognitive processes may prove to be helpful
in both establishing a theory of animal memory and testing
the scope and power of human memory theories. There may well
be relevant phenomena inaccessible through the use of human
subjects that will be clarified in studies using animals.
For example, animal research may help to separate those aspects
of human memory that are based on language form those that
are not. As Medin (1967) puts it "A theory of animal memory
may or may not turn out to be different from a theory of
human memory, but either way such information can be of great
value" (p. 115).

Memory in animal learning can be defined as stimulus

14
control by a stimulus that is no longer present. There are
several possible explanations for the ability of an animal
to maintain an item in memory. One of the first explanations
of short-term memory in pigeons was that proposed by Roberts
and Grant (1976). In Roberts and Grant's basic trace strength
and decay model a memory trace exists for each stimulus pre-
sented, and that memory trace decays in the absence of the
stimulus. More recent investigators have come to realize some
of the limitations of the trace-decay model of short-term
memory. Although much data can be explained in terms of the
relatively straightforward trace strength model, it also seems
entirely possible that the existence of a passive trace in
memory can be extended, within limits, through an active re-
hearsal process analogous to Type I or primary rehearsal in
humans. Behaviorists have traditionally defined rehearsal as
the maintenance of a stimulus that is no longer physically pre-
sent via some overt mediating behavior (Blough, 1959; Zentall,
Hogan, Howard & Moore, 1978). Wagner developed an information
processing model of animal memory hypothesizing that informa-
tion is maintained in STM via a more cognitive process of re-
hearsal (Terry & Wagner, 1975; Wagner, 1976; Wagner, Rudy &
Whitlow, 1973). The ability of pigeons to maintain an item
for longer periods of time than would be predicted by a trace
strength model seems to favor a rehearsal theory, whether
it be cognitive or behavioral. While the recent trend is
towards a cognitive interpretation of rehearsal and away from
a mediating behavior position, the present experiments will

not attempt to distinguish the type of rehearsal mechanism

15
being used. Rehearsal, as discussed in this thesis, could be
either cognitive or behavioral. Rather than the nature of the
rehearsal process the primary concern here will be the exis-
tence of an active as opposed to passive memory process in
the pigeon.

Delayed Matching to Sample

 

Out of the many procedures that have been developed to
study STM in pigeons, some of the most fruitful have been
methods that evolved from Hunter's (1913) delayed technique.
Various delayed response procedures have been used recently
to study STM in piegons (Grant & Roberts, 1973; Roberts, 1972;
Roberts & Grant, 1974; Shimp & Moffitt, 1974; Zentall, 1973).
These delayed response procedures are analogous to the STM pro-
cedures used with human subjects that are based on the Brown-
Peterson technique. These procedures basically involve pre-
senting an item to be remembered, removing the item from the
perceptual field for some interval, and testing for memory of
the item. Of these delayed response procedures the various
forms of delayed matching to sample (DMTS) have proven to be
quite suited for studying variables effecting animal short-
term memory.

The successive DMTS is one particular variation of DMTS
that has been used quite effectively with pigeons. This pro-
cedure was designed by Konorski (1959) and further developed
by Wasserman (1976) and Nelson and Wasserman (1978). The
procedure consists of a successive presentation of a pair of
stimuli (key-lights on a single key) separated by an inter-

stimulus or retention interval. Reinforcement occurs following

16
responses to the second (comparison) stimulus when this stim-
ulus matches the first (either exactly or symbolically). No
reinforcement is available on nonmatching trials. It is
necessary for the organism to maintain a respresentation of
the visual characteristics of the first, or sample, stimulus
in memory throughout the retention interval since that stimulus
is no longer physically present. This memory is then used in
a decision process concerning responding to the comparison
stimulus. It is possible to calculate a ratio of responses on
matching trials to total responding to the second stimulus. A
ratio of 1.00 indicates perfect matching performance and a
ratio equalling .50 indicates random chance levels of perfor-
mance (equal rates of responding on matching and nonmatching
trials). Wasserman (1976), using pigeons as subjects, keypecks
as responses, and red and green discriminative stimululi, re-
ported results of 80-90% discrimination ratios, indicating de-
finite stimulus control by the first stimulus.

Directed Forgetting in Pigeons

 

If there is a rehearsal process in pigeon STM, it should
be possible to control the amount of rehearsal (and the corres-
ponding retention) of stimuli in a manner analogous to the
human directed forgetting studies by using cues that direct
the animal to discontinue rehearsal, or "forget." Given that
the DMTS procedure is an effective tool in investigating STM
in pigeons it would follow that directed forgetting procedures
could be incorporated into the DMTS paradigm just as they are
incorporated into the Brown-Perterson paradigm in human memory

research. This procedure could be used to investigate the

17
possible use of rehearsal in the pigeon that is analogous to
Type I rehearsal to maintain items beyond the normal trace
life. Olton (1979) in his work with rats in radial-arm mazes
foresees work in this area when he raises the question as to
whether or not "resetting" (forgetting) can be placed under
discriminative control.

The notion of using directed forgetting techniques in
conjunction with DMTS procedures originated with a study by
Maki, Gillund, Hauge and Siders (1977) on the effect of the
cancellation of the comparison stimulus. Maki et al. found
that when the comparison stimulus was omitted from some trials
the matching accuracy on later trials was reduced to chance
levels. The effect of this unsignalled cancellation of the
comparison stimulus raised questions about the effects of a
signalled cancellation of the comparison stimulus (directed
forgetting). Maki followed this line of thought with a paper
presented at the 1979 meeting of the Midwestern Psychological
Convention. Maki and Anundson (Note 1), using a choice DMTS
procedure, presented birds with a white center key. A single
keypeck on this key produced a 2 second sample of either food
or no food. After an interstimulus interval of 1.5 seconds
remember (R) and forget (F) cues (.5 second flash of house-
light or no flash of houselight) occurred. On R cued trials
comparison stimuli of Red and Green keylights were presented
after the remainder of the delay interval, which averaged 10.3
seconds. Responses to red following food samples and to green
following no food samples were reinforced. Incorrect choices

terminated the trial. On F cued trials comparison stimuli were

18

not presented. Maki and Anundson ended sessions with 8 "probe"
trials, during which the comparison stimuli occurred on both R
cued and F cued trials. They found that choice matching per-
formance was at 75% on F cued probe trials as compared to 91%
on R cued probe trials.

An explanation for the ability to get cued forgetting in
a pigeon STM procedure could be offered based on the results
of human directed forgetting studies and Bjork's selective re-
hearsal hypothesis. It is possible that a rehearsal process
was utilized by the pigeon to maintain the characteristics of
the first stimulus throughout the retention interval on R cued
trials. This condition was functionally the same as no one at
all, or a standard DMTS procedure. The relatively poor reten-
tion on F cued trials can be attributed to a cessation of re-
hearsal elicited by the forget cue at the beginning of the re-
tention interval. This explanation is consistent with those
offered in human directed forgetting studies. According to
Bjork and Geiselman (1978):

In the item-by-item cueing paradigm, one might assume

that items are kept at a shallow level of processing

through maintenance or primary rehearsal until the

cue is presented. When a forget cue is presented, it

terminates or inhibits the processing that would go

on automatically without such a cue. (p. 349)
Temporal Location of the Cue

One implication of the above explanation for the directed
forgetting effect is that the temporal relation of the forget
cue to the TBF item is a crucial variable in determining the

effectiveness of that cue. The longer the delay between the

sample stimulus and the forget cue the more processing a TBF

19
item would receive. Also, the shorter time from the F cue
until the onset of the comparison, the less time there is for
forgetting in the absence of rehearsal (either through decay
or interference) to occur. If the superior matching perfor-
mance of R cued trials over F cued trials is the result of
differential amounts of rehearsal, or the result of differen—
tial amounts of time since rehearsal termination, varying the
temporal location of the cue within a constant length reten-
tion interval will reduce the difference in matching perfor-
mance between R and F cued conditions. In other words, delay-
ing the cue will reduce the effectiveness of the F cue.

One would probably not predict that varying the temporal
location of an R cue would have any effect on performance in
pigeon directed forgetting studies. In human research, where
the temporal location of an R cue does have an effect, it has
been demonstrated that pre-cue rehearsal is a rote maintanance
rehearsal, while post-cue rehearsal on R cued trials is a
more elaborative secondary rehearsal (Bjork & Geiselman, 1978).
There is no evidence for anything more than a rote maintenance
rehearsal pre- or post-cue in the pigeon. Since elaborative
rehearsal is closely associated with long-term memory, it is
probably not a factor in this paradigm, at least according to
Roberts and Grant (1976), who claim that long-term memories
of events occurring in DMTS trials are not established in the
pigeon. Since the directed forgetting effect in pigeons is
then due solely to differential amounts of rote primary re-
hearsal this effect can be seen as directly analogous to re-

cognition (but not recall) tests in human directed forgetting

20
studies. As previously pointed out, these recognition tests
are influenced by Type I, but not Type II, rehearsal (Glenberg
& Adams, 1978; Glenberg, Smith and Green, 1977).

Assuming that the directed forgetting effect in pigeons
is the result of differential amounts of rehearsal, (or differ-
ential amounts of lack of rehearsal) the temporal position of
the F cue is a crucial variable. Based on the above model
primary rehearsal occurs both before and after the cue on R
trials. This rehearsal only occurs before the cue on F trials.
The total rehearsal on F cued trials increases with longer
delays between the sample and the cue, resulting in decreased
differential rehearsal between R and F cued trials. The total
time in the absence of rehearsal (the post-cue interval) de-
creases with longer delays between the sample and the cue (in
a constant length retention interval). With an immediate cue
forgetting in the absence of rehearsal occurs for the entire
duration of the retention interval. The closer the onset of
the F cue gets to the end of the retention interval, the less
time there is for forgetting to occur before the onset of the
comparison stimulus. The combined factors of more rehearsal
and less forgetting should decrease the effectiveness of the
F cue (i.e., the pigeon will be less able to forget on F cued
trials the later the F cue occurs).

There is much support in the literature on human directed
forgetting for the notion that the longer the delay between
TBF items and the F cue the less effective the one will be.
Timmons (1974) designed an experiment to explore the effect of

varying the amount of processing time between the presentation

21

of a block of words and the forget cue. Timmons found that
the time of one presentation was a critical variable in the
recognition of TBF items, and that when the cue is delayed
until just prior to recall the TBF items received just as much
processing as if no cue had been presented at all. These items
were more likely to be recognized on a subsequent test than
items that were not maintained in STM as long, due to earlier
cueing. Reed (1970) also demonstrated that the greatest effect
of a forget cue was obtained when the cue occurred at the be-
ginning of the retention interval rather than the end.

The effect of delayed cueing has also been demonstrated
in item by item cueing procedures, which more closely parallel
the DMTS procedure used with pigeons. Woodward et a1. (1973)
felt that an item would be better remembered and less easily
forgotten the greater the amount of rehearsal there was that
was devoted to that item. By varying the rehearsal time bet-
ween each item and its corresponding cue they established that
the final rec0gnition increased systematically with the amount
of rehearsal. As previously described, Wetzel and Hunt (1977)
used a between list variation of the cue location, rather than
the within list variation of Woodward et al., to demonstrate
the effect of amount of rehearsal on both recall recognition.
The between list variation eliminated the equality of rehearsal
for items that initially had different word-cue intervals.
Wetzel and Hunt's study compared short and long delay cueing
conditions for equal retention intervals. Their long delay
condition utilized pre-cue intervals of 1, 4, 8, and 12 seconds.

They clearly demonstrated that immediate cueing produced much

22
more efficient forgetting than delayed cueing, and that this
efficiency was a function of the length of the word-cue inter-
val. Clearly the greater opportunity for rehearsal prior to
the onset of the F cue decreased the ability of the subjects
to forget or discard that memory. It is precisely this effect
that is the main focus of the present study.

To recapitulate, it is assumed that the greater matching
performance following an R one over the performance following
an F cue is due to the pigeon's ability to utilize the F cue
to terminate rehearsal processes. Since R cued items are re-
hearsed both before and after the cue, and F cued items are
rehearsed only before the cue, it is assumed that the differ-
ential performance is a function of the differential amounts
of rehearsal, the differential amounts of time without re-
hearsal, or some combination of the two. By varying the
temporal position of the cue within the retention is should be
possible to control the amount of differential rehearsal and
forgetting due to a variation in the pre- and post-cue inter—
vals. Total rehearsal on F trials is varied through the varia-
tion of the pre-cue interval while total rehearsal on R cued
trials remain constant. The net effect of a delayed cue
should be negligible on R trials, but greater processing and
less forgetting should produce increased retention on F trials,
making the F cue less effective. Thus the matching perfor-
mance on a delayed F trial should fall between the level on
immediate F cued trials and the level on R cued trials, as
a function of length of delay.

The initial phase of the present experiment replicates

23
Maki and Anundson's directed forgetting effect using a suc-
cessive, rather than choice DMTS procedure. After demonstrating
good memory on R cued trials and poor memory on the F cued
trials the temporal location of the cues will be varied within
the retention interval as described above. The importance of
such a manipulation is twofold. In addition to investigating
the effects of manipulating the one location on matching per-
formance this manipulation has special importance in the inter-
pretation of the immediate cue data of both this and Maki and
Anundson's experiment. In both procedures the memory on F
cued trials is assessed on "probe" trials which instruct the
pigeon that the comparison stimulus will not occur and then
follow that cue with a comparison stimulus. If one assumes
only a trace-decay model and does not allow for rehearsal pro-
cesses, it might be argued that the directed forgetting effect
obtained in the two studies was merely an artifact of the
testing procedure used. The forgetting that is demonstrated
by poorer matching performance on probe trials (F cued) could
be explained by the fact that the occurrence of the comparison
stimulus following a forget cue is contrary to training and
is therefore disrupting. If this is the case, the forgetting
could be just as easily explained as a function of retro-
active interference of a passive trace (causing increased
decay) as it could be termination of an active rehearsal pro-
cess. The immediate cue data are confounded by the fact that
both reduced rehearsal and disruption due to the conflicting
occurrence of the forget cue and the comparison stimulus

would produce the same behavioral results--reduced matching

24
performance. In the present experiment, however, these two
explanations are pitted against one another and the controlling
variable should become clear. In the delayed cueing condition
the amount of pre-cue rehearsal time is greater than the
amount of pre-cue rehearsal time in the immediate cueing con-
dition. If termination of an active maintenance process is
the controlling variable in the poor matching performance on
F cued trials under the immediate cueing condition, the delay-
ed cueing condition should not produce such a poor matching
performance. Matching performance should improve due to a
stronger memory trace of the sample stimulus (due to either
more rehearsal or less time since rehearsal terminations).
In other words, the forget cue would be less effective in the
delayed condition than it is in the immediate condition. If,
on the other hand, disruption is the cause of poorer matching
performance following an F cue one would not expect better
matching performance on delayed cue trials. The poor matching
performance that occurs on F cued trials when the cue is
immediate should also occur when the cue is delayed because a
delayed cue would be at least as disrupting as an immediate
due, if not more so (cf. Roberts and Grant's 1978 work on the
effect of the point of interpolation of a light within the
retention interval). If disruption occurs due to an incongru-
ent pairing of an F cue and a second stimulus, this pairing
should be incongruent regardless of the temporal occurrence
of the F cue, since training will occur with both immediate
and delayed cueing conditions. A delayed F cue should be just

as "effective" as an immediate F cue under this model. Thus

25

the prediction of a disruption hypothesis would be equal or
inferior matching performance for the delayed cueing condition
as opposed to immediate cueing, while the rehearsal hypothesis
would predict greater matching performance (less able to
forget) in the delayed cue condition.

Pilot data from cue location manipulations have favored
a rehearsal termination hypothesis. Further questions can
therefor be asked regarding the factors that lead to the ef-
fectiveness of an immediate cue as Opposed to the reduced ef—
fectiveness of a delayed cue. In the design of the present
experiment as has been described thus far there are three vari-
ables--duration of the retention interval, duration of the
pre-cue interval, and duration of the post-cue interval--that
are related in such a way that only one can be held constant
at a time leaving the other two variables confounded. In the
experiment as described thus far the retention interval will
be held constant at 4 seconds while pre-cue intervals of 0,
2, and 3.5 seconds will be paired with post-cue intervals
of 3.5, 1.5, and 0 seconds respectively (the cue will be 0.5
seconds). As has been alluded to, the result is that it
is unclear whether the primary influence of the expected re-
duced effectiveness of delayed F cues is increased rehearsal
(during increased pre-cue intervals) or decreased forgetting
in the absence of rehearsal through decreased post-cue inter-
vals. In human studies it can be shown that increased re-
hearsal leads to better memory. In the pigeon it may be that
rehearsal does not strengthen the memory trace but merely

maintains in enough to postpone the occurrence of forgetting

26

through either decay or interference. If this hypothesis is
true, the critical determinant of amount of forgetting should
be the amount of time from the termination of rehearsal, as
controlled by the F cue, until the presentation of the com-
parison stimulus (the post cue interval). If amount of re-
hearsal is the critical determinant of the amount of for-
getting the crucial variable would then be the pre-cue inter-
val. Should the strength of the memory for the sample vary
with cue location as is expected, the final phase of this
experiment will be an attempt to determine which of these
intervals--pre or post-cue--plays the more important role in
producing this effect. This will be accomplished by varying
the retention interval and comparing performance against one
condition where the pre-cue interval is held constant while
the post-cue varies, and against another condition where the
post-cue interval is held constant and the pre-cue interval

varies.

METHOD

SUBJECTS

Two adult experimentally naive White Carneaux pigeons
were used. Birds were maintained at 80% i 15 g of their free-
feeding weights. Birds were individually housed in a tempera-
ture controlled and constantly illuminated room and had free

access to water and grit.

APPARATUS

 

A standard Lehigh Valley Electronics three key condition-
ing chamber was used. Interior dimensions were 35 x 35 x 30 cm.
Only the center 2.5 cm. response key, which required a force
of 0.15 N for activation, was used. The response key was trans-
illuminated with either a red (606 nm) or green (555 nm) stimu-
lus from an IEE projector (Model # : 10-3723-757-L). The key
was located above the 5 x 6 cm magazine opening. Above the
key was a 28 V houselight (CM 1820). Also located on the
intelligence panel was a circular speaker gril. During re-
inforcement a 28 V light (SYLVANIA 28 PSB) within the magazine
enclosure was illuminated. Activation of a Lehigh Valley
Electronics photoelectronic relay initiated the reinforcement
timer. An exhaust fan, located on the wall opposite the res-
ponse panel, partially masked extraneous noises. Experimental
events were controlled by standard electromechanical program-
ming equipment located in an adjacent room, with a paper tape

reader controlling the sequence of events.

27

28

PROCEDURE

 

Both birds were trained to approach and eat mixed grain
from the magazine. Birds were placed in the lighted test
chamber with the magazine elevated, lighted, and food easily
visible. A photoelectric beam was broken when the bird ate
from the magazine, and 2.5 seconds later the magazine lowered
out of reach. Thirty presentations of food occurred on a
variable time schedule of 45 seconds.

For the next three sessions birds were autoshaped accord-
ing to the Brown and Jenkins (1968) autoshaping procedure.

Each autoshaping session consisted of 50 trials during which

a six second stimulus presentation of either a red or green key-
light was immediately followed by reinforcement. The mean in-
terval was 45 seconds. Throughout the entire experiment re-
inforcement consisted of 2.5 seconds access to mixed grain.
After three autoshaping sessions both birds were reliably
pecking both red and green stimuli.

Following autoshaping birds were trained on the successive
delayed matching to sample task following the procedures out-
lined in Table l. The stimulus parameters followed Nelson
and Wasserman (1978) to obtain maximum matching performance.
Typically, the sample was presented for 12 seconds, followed
by a retention interval during which no stimulus appeared un-
til the onset of the comparison stimulus. Keypecks to the
comparison stimulus when it was the same as the sample (matched)
were reinforced, and keypecks during nonmatching comparison
stimuli were extinguished. The intertrial interval was 30

seconds.

29
Table 1

Training Procedures for Phase I
and the Transition Phase

 

 

Phase I: Delayed 12 Second 5 Second
Matching Sample Delay Interval Comparison
to Sample Stimulus Stimulus
Training

RED X sec. RED: Fl 5 sec.
RED X sec. GREEN: extinc-
tion
GREEN X sec. RED: extinc-
tion
GREEN X sec. GREEN: F1 5
sec.
Transition Phase Onset of Retention Onset of
Interval Comparison Stimulus
12 R cues
24 R cues
36 R cues
36 R cues 4 F cues
36 R cues 8 F cues
36 R cues 12 F cues
36 R cues 20 F cues
36 R cues 28 F cues

(Final Directed— 36 R cues 36 F cues
Forgetting Stage)
36 R cues 36 F cues Tone
From the responses to the matching and nonmatching com-
parison stimuli discrimination ratios were calculated as a
measure of matching accuracy or performance. This ratio was
calculated by dividing the responses during matching comparison

stimuli by the total number of response during comparison

stimuli, both matching and nonmatching. A discrimination ratio

30
of 1.00 indicates perfect matching performance with responding
during the comparison stimuli occurring exclusively on match-
ing trials. A ratio of .50 indicates chance levels of match-
ing performance, with equal levels of responding occurring on
matching and nonmatching trials.

During training the duration of the retention interval
was initially set at one second. This interval was maintained
until a bird performed above an 80% discrimination ratio for
two consecutive days. Retention intervals were increased in
one second increments each time the above criterion was met
until the terminal value of four seconds was reached. Once
this level of performance was met and maintained, the intro-
duction of remember (R) and forget (F) cues (vertical and
horizontal lines presented on the key) began according to
the schedule on the bottom of Table 1. During this transition
phase between basic DMTS and DMTS with directed forgetting
the 0.5 second cues occurred immediately after the termination
of the sample stimulus. The key remained dark for the re-
mainder of the retention interval. Cued trials were randomly
interspersed among noncued trials during the transition phase.
These cued trials are procedurally the same as the trials in
Phase II (Table 2), with the second stimulus not occurring
following a forget cue. The transition phase proceeded to
the next level each time performance met the 80% discirmina-
tion ratio criterion. Once all trials were being cued, a
40 msec 1,000 Hz tone of approximately 80 db was added to
the procedure. This tone occurred contiguous with the onset

of the comparison stimulus as an additional cue indicating

31

the presence of that stimulus (the importance of the tone
is on F cued probe trials where after presenting the forget
cue to the bird, the comparison stimulus is presented. Since
birds often turned away from the key upon seeing an F cue
it was necessary to alert the bird as to the presence of the
comparison stimulus on those trials in order to accurately
assess memory on those trials).

Table 2 outlines the procedures used in Phases II, III,
IV and V. All followed the same basic procedure, with the
defining characteristic of each phase being the temporal lo-
cation of the cues within the retention interval. For Phase
II the cues occurred immediately after the termination of the
sample stimulus (0 second delay). For Phase III the 0.5
second cues occurred as late as possible within the 4 second
retention intervals, in other words at a 3.5 second delay.
During Phase IV cues were located in the middle of the 4
second retention interval at a 2 second delay. For Phase V
the retention interval was shortened from 4 to 2.5 seconds
and the cues occurred after a 2 second delay. Each of these
phases is pictorially represented at the bottom of Table 2.

During training on all four phases the comparison stim-
ulus was only presented on R cued trials. On F cued trials
the retention interval was followed directly by the ITI.
Training proceeded on each phase until the bird performed at
or above the 80% criterion for five consecutive days. Once
the criterion was met probe sessions began. For each phase
five probe sessions, consisting of 68 baseline and 4 random-

ly located probe trials, were presented. Probe sessions that

32
Table 2
Training and Testing Procedures
For Phases II, III, IV, and V
Phase II: Training
Sl---0.5 sec R cue---3.5 sec---SZ(matching)---Rf---ITI
Sl---0.5 sec R cue---3.5 sec---SZ(nonmatching)---ITI
Sl---O.5 sec F cue---3.5 sec-~ITI
Phase II: Testing (5 sessions)
Sl--0.5 sec R cue---3.5 sec---SZ(matching)--Rf—--ITI
Sl--O.5 sec R cue---3.5 sec---SZ(nonmatching)---ITI
Sl--0.5 sec F cue---3.5 sec---SZ(matching)--Rf---ITI
Sl--0.5 sec F cue---3.5 sec--SZ(nonmatching)---ITI
Phase III: Training and Testing
Sl---3.5 sec---0.5 sec cue---82 or ITI
Phase IV: Training and Testing
Sl-—-2 sec---0.5 sec cue---l.5 sec---SZ or ITI
Phase V: Training and Testing

Sl---2 sec---O.5 sec cue---SZ or ITI

 

 

 

 

 

 

ITI SAMPLE RETENTION COMPARISON* ITI
INTERVAL
Phase II __J E T 1
Phase III .4-J 1 J 1

 

 

 

 

 

Phase V __J L_-| * L

 

 

 

* On R cued and Probe trials only

--— R/F cue

33

failed to maintain a 75% discrimination ratio on baseline
trails were eliminated from the final analysis. Probe
sessions were alternated with as many sessions as were ne-
cessary to maintain the 80% discrimination ratio. After data
was collected on five probe sessions the bird proceeded to
training on the next phase.

On probe trials the F cue was presented and was followed
by the comparison stimulus, contrary to training (see Table 2).
One of each of the four combinations of red and green was used
as a probe trial within a single probe session. The order of
the probe trials within a session was balanced between sessions.
Reinforcement was available following matching probes and ex—

tinction was in effect on nonmatching probes.

RESULTS

Table 3 shows the response rates during comparison stim-
uli for each bird under the various conditions. From these
response rates the discrimination ratios in Figure l were
calculated, using the formula previously described. Again,
a ratio of 1.00 indicates perfect matching performance and
a ratio of .50 indicates chance levels Of performance. Only
the discrimination ratios for the 4 second retention interval
conditions (Phases II, III, and IV) are plotted on this figure.
Under the 0 second delay condition it can be seen that birds
1162 and 1067 had matching accuracies of .91 and .86 respec-
tively on R cued trials, while performance on F cued trials
was greatly reduced to .58 and .54. By referring to Table 3
it can be seen that these near chance levels of performance
were primarily due to increased levels of responding on non-
reinforced nonmatching trials (red-green and green-red) rather
than a reduction in levels of responding on reinforced matching
trials (red-red and green-green).

In Figure 1 it is clear that the temporal location of an
R cue had little or no effect on performance on those trials,
especially for bird 1162 where all 3 cue locations produced
matching accuracy of .91. The temporal location of an F cue
within the retention interval substantially influenced be-
havior on those trials, however, as can be seen in the figure.
The longer the onset of the cue was delayed the better

34

Bird 1067

 

RIa
delay

4 sec
0 sec
4 RI

2 delay

SOC
sec

4 sec RI
3.5 sec
delay

2.5 sec RI
0 sec delay

Bird 1162

 

4 sec RI
0 sec delay

4 sec RI
2 sec delay

4 sec. RI
3.5 sec

delay

2.5 sec RI
0 sec delay

a
RI =

35

Table 3

Responses per minute during com-

parison stimuli following Remember

(R) and Forget (F) cues during

4 and 2.5 second retention inter-
vals with various cue delays.
Trial types are red—red (RR),
green-green (GG), red-green (RG)
and green-red (GR).

RR

R Cued

GG

RG

GR

 

 

195.3

249.6

281.7

262.8

191.7

142.5

167.4

167.1

196.5

247.5

248.7

260.4

181.2

111.9

148.5

122.4

34.2

53.1

17.1

12.3

12.9

10.8

12.6

34.2

Retention Interval

28.8

19.2

24.6

12.0

25.2

12.0

18.3

21.3

F Cued

RR GG RG GR

160.8 151.2 117.6 151.2
237.6 204.0 81.6 187.2
276.0 201.6 31.2 74.4
230.4 232.8 28.8 57.6
158.4 132.0 79.2 127.2
158.4 98.4 43.2 19.2
136.8 124.8 2.4 7.2
141.6 105.6 4.8 19.2

(interstimulus interval)

36

FIGURE 1. Matching performance as a function of cue
delay on remember (R) and forget (F) cued
trials.

37

 

 

Sufi >33 “3

 

 

0U" NOIIVNIWIUOSIG

38
matching performance was that occurred on those trials. Also,
the later the cue the less difference existed between R cued
and F cued trials. After a delay of 3.5 second F cues almost
completely lost their effectiveness, with performance on those
trials highly similar to performance on R cued trials.

Figure 2 presents the mean number of keypecks each bird
emitted during the retention intervals for the various cue
delays and for the various combinations of red and green and
of remember and forget cues. This figure presents the re-
tention interval keypecks that occurred during the five-day
baseline periods before testing on Phase II, III and IV.

Mean keypecks after red and green always differed by less than
one keypeck when comparing keypecks under either remember or
forget conditions for any of the cue delays for each indi-
vidual bird. In other words there was no difference in key-
pecking behavior following red and green samples. However,
there are differences in the amount of keypecking that occurs
on remember versus forget cued trials. These differences
resulted from the fact that generally birds pecked the key
during the retention interval until the presentation of the
cue. If a remember cue was presented pecking continued until
the presentation of the comparison stimulus. If a forget cue
was presented keypecking stopped and the bird usually began
engaging in other behaviors (intertrial behaviors such as
exploring and preening, since an F cue indicated the end of

a trial on all trials except probes). Consequently, few key-
pecks occurred during the retention interval when there was

no delay between the end of the sample and the presentation

39

FIGURE 2. Mean keypecks during 4 second retention
intervals as a function of one delay and
remember (R) and forget (F) cues.

4()

 

 

 

 

auau . auau a

Tm

1:—

 

rm—

 

ro—

 

 

rm—

 

:d: Sm m.m

ouau & auao a

 

 

 

 

 

=3: Sm ~

rm

ta—

ta.

 

In

re.

rm—

 

auau . case a

 

 

 

 

 

.Illnnnulllj
rm
f.
rm.
$2..
IHMIJ
rm
I .2
....u go... HHHHHH rm.
2.. 2:. I 32..
:3: 3m 6

83(3)“!!! NVJW

41

FIGURE 3. Comparison of matching performance on Phase
V (control condition) to Phases III and IV.

42

 

m.~

 

83V .2235. 3:552

mac—mom e \uaomxg ~
mac—m9. 3 \ “=8...— ~
mac—mom c\u=ou¢m mg

m

O
D

Q
33

.N

O
I
4

3:9

3:.—

 

OllVll NOIIVNIWIHOSIO

43
of an F cue, more occurred when the F cue was delayed 2
seconds, and many occurred when the cue was delayed 3 1/2
seconds. The data on the number of keypecks during the
retention interval is highly similar to the matching perfor-
mance depicted in Figure l, with R cued trials remaining re-
latively constant and F cued trials increasing as a function
of the cue delay.

Figure 3 presents the data obtained on Phase V in rela-
tion to the data obtained in Phases III and IV. The latter
data, from conditions with 4 second retention intervals and
2 and 3.5 second cue delays respectively, is the exact same
data from those cue delays on Figure l. The new point of
interest is that from Phase V, where the retention interval
is 2.5 seconds and the cue delay is 2 seconds. By varying
the retention interval in this fashion it is possible to
compare the Phase V point with each of the other points. In
comparing the Phase V point with the 3.5 second delay point
the post-cue interval is held constant at 0 seconds while the
pre-cue interval is increased from 2 to 3.5 seconds. In com-
paring the Phase V point with the 2 second delay point the
pre-cue interval is held constant at 2 seconds and the post-
cue interval is increased from 0 to 1.5 seconds. For both
birds it can be seen that the former comparison, increasing
the pre-cue interval, had very little effect on matching per-
formance (.84 vs. .82 for bird #1067; .91 vs. .96 for bird
#1162). On the other hand, the latter comparison, which
increases the post-cue interval, clearly demonstrates that

with a longer period from the end of an F cue until the

44
presentation of the comparison matching performance sharply

declines, even at a difference of only 1.5 seconds (.84 vs.

.62 for bird # 1067; .91 vs. 80 for bird #1162).

DISCUSSION

 

The results of this experiment present extremely strong
evidence in favor of an active memory processing in the
pigeon. If short-term memory in the pigeon is a passive pro-
cess that is not under the control of the organism, remember
and forget cues could not gain stimulus control. Therefore,
performance with immediate cues should be similar for both
remember and forget cued trials. The data Obtained with
immediate cues in Figure l are extremely consistent with
Maki's directed forgetting results in that matching perfor-
mance is very good on remember cued trials and greatly re-
duced on forget cued trials, supporting an active processing
hypothesis. The results with delayed cues, in that a de-
layed F cue is less effective the later it occurs within the
retention interval, demonstrate that the effect with immedi-
ate cues is due to different memory strengths on R and F cued
trials that seems to have resulted from differential re-
hearsal. Apparently when an R cue is presented the pigeon
rehearses during the entire retention interval, both before
and after the cue regardless of its temporal location. On
F cued trials it appears as if the pigeon rehearses until
the F cue is presented, and terminates rehearsal upon the
presentation of that stimulus. This behavior closely par-
allels the behavior reported in human directed forgetting
studies by Bjork and Geiselman (1978) and others.

The notion that the immediate cue data in this and in

45

46

Maki's study could be due to a disruption caused by the test-
ing procedure is clearly not supported. Such a hypothesis
would predict equal disruption regardless of the temporal lo-
cation of an F cue. This is clearly not the case. Rather,
F cues lose their effectiveness when they are delayed within
the retention interval to the point where a cue at the end of
the retention interval is barely different from R cued trials,
if at all. This appears to be due to the changes in differ-
ential rehearsal. The less a stimulus is maintained via re-
hearsal during the retention interval, the poorer the memory
for that stimulus will be at the end of the retention interval.

The results presented in Figure 2 show that when pigeons
rehearsed during the retention interval they also keypecked.
This data would not lead one to conclude that keypecking was
the rehearsal process, however, in light of the fact that
keypecking was nondifferential following red and green sample
stimuli. However, it is more likely that keypecking is a
collateral behavior occurring simultaneously with rehearsal.
If this is the case it is easier to think of rehearsal as a
cognitive process, since the maintenance of two behaviors-—
one sample specific and one nondifferential--does not seem
parsimonious. In observing the behavior of birds during the
retention interval it was noted that birds stayed focused on
the key (usually keypecking) for the entire retention inter-
val on R cued trials. The consistently high matching perfor-
mance on R cued trials indicates that rehearsal was maintain-
ed throughout the retention intervals on those trials. On F

cued trials birds stayed at the key only until the cue. When

47
an F cue was presented birds not only stopped keypecking but
also left the key and began other behaviors that proved to
interfere with the memory of the sample stimulus. The function
of matching performance on F cued trials indicates that re-
hearsal occurred for increasing periods of time as a function
of one delay, probably during the pre-cue interval. It is my
opinion, then, that during the time attention was focused on
the key a cognitive rehearsal process was occurring. Attention
was focused on the key in order to reduce interference from
other stimuli and events. As attention was focused on the key
during rehearsal the natural response of the pigeon was to peck
the key, but that keypecking behavior was not itself the re-
hearsal process. Whether keypecking was necessary or whether
focused attention alone would have been sufficient to reduce
interfering events is not clear.

In saying that the results of Figure l are due to varying
amounts of differential rehearsal it should be noted that im-
plied in this term are two contributing factors: differential
amounts of time when rehearsal was occurring and differential
amounts of time when rehearsal was not occurring. On F cued
trials the former relates to the pre-cue interval and the latter
relates to the post-cue interval. The results in Figure 3 show
which of these factors played the major role in F cues becoming
less effective as cue delay increases. If increasing the pre-
cue interval produced the decreasing effectiveness of the F
cues one would predict that the new point on the left from
Phase V (2.5 second retention interval) would be similar to

the lower of the two points on the right and different from

48
the higher of the two points. This prediction stems from the
fact that in the former comparison the pre-cue interval is
held constant whereas in the latter comparison the pre-cue in-
terval is varied. If decreasing the post-cue interval pro-
duced the decreasing effectiveness of the F cues one would pre-
dict the Opposite results; that the new point would be similar
to the higher of the two points on the right and different
from the lower point, since the former comparison holds the
post-cue interval constant while the latter comparison varies
the post-cue interval. Figure 3 indicates that performance on
Phase V was more similar to the higher of the two points on
the right than it was to the lower. For both birds it can be
seen that increasing the amount of rehearsal (pre-cue interval)
from 2 to 3.5 seconds had very little effect on memory as
measured by matching performance. In contrast, increasing the
amount of time after the termination of rehearsal (post-cue
interval) from 0 to 1.5 seconds had a large effect on memory.
Longer periods of time without rehearsal resulted in weaker
memory at the time of testing. In other words the factor that
produced reduced F cue effectiveness for delay cues was reduced
post-cue intervals, or time since the termination of rehearsal,
rather than increased rehearsal.

The result that increased rehearsal does not increase the
strength of the memory is one point where the present study
differs from the results found in human memory processing
studies. The findings of Glenberg, Smith and Green (1977),
Meunier, Ritz and Meunier (1972), Woodward et a1. (1973), and

Wetzel and Hunt (1977) demonstrated that there was a direct

49
relationship between amount Of Type I or maintenance rehearsal
and performance on a recognition test. In pigeons it appears
that the rehearsal process does not strengthen the memory
trace but merely maintains it enough to postpone the occurrence
of forgetting. The fact that birds are only able to maintain
a memory for 4-6 seconds under the present experimental condi-
tion seems to indicate that memory loss is even occurring
during the rehearsal process. Rehearsal in the pigeon there-
fore serves to delay or slow down the forgetting that inevitably
occurs. This forgetting occurs despite rehearsal processes, but

would occur much more rapidly without rehearsal.

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