Learn Behav (2014) 42:40–46
DOI 10.3758/s13420-013-0122-x
Midsession reversals with pigeons: visual versus spatial
discriminations and the intertrial interval
Jennifer R. Laude & Jessica P. Stagner &
Rebecca Rayburn-Reeves & Thomas R. Zentall
Published online: 17 September 2013
# Psychonomic Society, Inc. 2013
Abstract Discrimination reversal learning has been used as a
measure of species flexibility in dealing with changes in reinforcement contingency. In the simultaneous-discrimination,
midsession-reversal task, one stimulus (S1) is correct for the
first half of the session, and the other stimulus (S2) is correct for
the second half. After training, pigeons show a curious pattern
of choices: They begin to respond to S2 well before the reversal
point (i.e., they make anticipatory errors), and they continue to
respond to S1 well after the reversal (i.e., they make perseverative errors). That is, pigeons appear to be using the passage of
time or the number of trials into the session as a cue to reverse,
and are less sensitive to the feedback at the point of reversal. To
determine whether the nature of the discrimination or a failure
of memory for the stimulus chosen on the preceding trial
contributed to the pigeons’ less-than-optimal performance, we
manipulated the nature of the discrimination (spatial or visual)
and the duration of the intertrial interval (5.0 or 1.5 s), in order
to determine the conditions under which pigeons would show
efficient reversal learning. The major finding was that only
when the discrimination was spatial and the intertrial interval
was short did the pigeons perform optimally.
Keywords Discrimination learning . Midsession reversal .
Spatial . Visual . Timing . Intertrial interval . Pigeons
The ability of an animal to adapt to environmental change
depends on its ability to learn that the reward value of a stimulus
can suddenly change. To the degree that the animal is influenced
only by the accumulated reinforcement history associated with
J. R. Laude : J. P. Stagner : T. R. Zentall (*)
Department of Psychology, University of Kentucky, Lexington,
KY 40506-0044, USA
e-mail: zentall@uky.edu
R. Rayburn-Reeves
University of North Carolina, Wilmington, NC, USA
the stimuli that it has experienced, its ability to respond to a
change in reward value should be rather slow, whereas if it is
able to benefit from feedback from the outcome of the preceding
trial, it should be able to acquire new learning faster, perhaps by
learning to ignore irrelevant cues and learning to quickly inhibit
earlier behavior.
One approach to assessing an animal’s learning-to-learn
ability is to train the animal on a serial reversal task in which
the animal is given a simultaneous discrimination. Following
acquisition, the discrimination is reversed (i.e., what was once
correct is now incorrect), and once the animal has acquired the
reversal, the discrimination is reversed repeatedly (e.g.,
Mackintosh, McGonigle, Holgate, & Vanderver, 1968). If
one uses original learning as a baseline against which to
measure improvement, one should be able to control for the
difficulty of the original discrimination and thereby assess
individual differences, and even make comparisons among
different species. That is, the degree of improvement with
successive reversals, relative to the original acquisition baseline, should be a measure of the animal’s cognitive flexibility
(Bitterman, 1975). Research has shown that a variety of
animals, including apes and monkeys (Beran et al., 2008;
Warren, 1966), horses (Martin, Zentall, & Lawrence, 2006),
rats (Bushnell & Stanton, 1991; Reid & Morris, 1992;
Williams, 1972), and birds (Bond, Kamil, & Balda, 2007;
Ploog & Williams, 2010) show substantial improvement with
reversals, suggesting that, since it is so prevalent, this type of
flexibility should have adaptive value (Shettleworth, 1998).
Furthermore, serial reversal studies have shown that the variability in improvement over reversals differs among species,
suggesting that some species can quickly adjust to changes in
the value of stimuli as a function of feedback.
When a reversal has been experienced repeatedly, the optimal strategy with this task would be to base one’s choice
on the consequences of the last trial. If the previous response
was rewarded, one should stay with it; if it was not rewarded,
one should shift to the alternative response. Humans are quite
Learn Behav (2014) 42:40–46
good at adopting this optimal strategy (Bechara, Tranel, &
Damasio, 2000), whereas other species typically do not show
such optimal reversal performance.
A variation of the serial reversal procedure is one in which
each session, involving a simple simultaneous discrimination,
begins with one stimulus (S1) as the correct (positive, S+)
stimulus and a different one (S2) as the incorrect (negative, S–)
stimulus (S1+, S2–), and halfway through the session the
discrimination reverses (S2+, S1–; Rayburn-Reeves, Molet, &
Zentall, 2011; see also Cook & Rosen, 2010; Mackintosh
et al., 1968). Unlike other serial reversal procedures, two
novel aspects of this procedure are that the correct response
at the start of each session is predictable and that the reversal
occurs at a predictable point in each session.
In Rayburn-Reeves et al.’s (2011) procedure, for each
pigeon, one stimulus was randomly assigned as the first
correct stimulus (S1), and responses to that stimulus and not
the other (S2) were reinforced for the first half of each 80-trial
session (S1+, S2–). However, for the last half of the session,
the contingencies were reversed (S1–, S2+). For a given
pigeon, S1 was always the same from session to session.
The results indicated that the pigeons made two distinct types
of errors: anticipatory errors (choosing S2 prior to the reversal)
and perseverative errors (choosing S1 after the reversal). This
pattern of results suggests that the pigeons were not very
sensitive to the feedback from the outcome of the most recent
trial(s) and that they were using the number of trials or the
passage of time into the session as a cue to estimate the point
of the reversal. That is, although use of the number of trials or
the time into the session resulted in reasonable overall choice
accuracy (near 90 % correct), they responded suboptimally
because they did not receive as much reinforcement as they
could have had, had they used the cues provided by their
recent history of reinforcement (a single error).
In an attempt to reduce the relevance of time into the session
as a dominant cue, Rayburn-Reeves et al. (2011) varied the
location of the reversal in the session in an unpredictable
manner from session to session. Specifically, in each session,
the reversal could occur at one of five different locations in
each session (after Trial 10, 25, 40, 55, or 70). Surprisingly,
after 100 sessions of training, they found that when the reversal
occurred early in the session, the pigeons showed a large
number of perseverative errors but few anticipatory errors,
and when the reversal occurred late in the session, the pigeons
showed a large number of anticipatory errors but few perseverative errors. In addition, the total number of errors increased,
the further from the middle of the session the reversal occurred.
Thus, even when the reversal location was unpredictable, the
number of trials or the time into the session continued to
influence sensitivity to the reversal. Furthermore, when the
reversal occurred at an unpredictable point in the session, the
total number of errors actually increased relative to when the
reversal occurred at a predictable point in the session. That is,
41
in part, the pigeons appeared to continue to use time or trials
into the session as a cue to reverse, suggesting that their ability
to use cues provided by changes in the value of the visual
stimuli was somehow impaired.
It is possible, however, that because the visual cues alternated randomly between the two locations (left and right), the
only relevant cue for the pigeons was whether a response to the
previously chosen color was reinforced. In this respect, optimal choice required that the spatial location of the stimulus
associated with reinforcement had to be ignored. To encourage
the pigeons to use the stimulus selected and the outcome of the
previous trial as the basis for choice on the current trial,
Rayburn-Reeves, Stagner, Kirk, and Zentall (2013) converted
the task to a spatial (left, right) midsession reversal discrimination, rather than the color midsession reversal discrimination
that had been used by Rayburn-Reeves et al. (2011); however,
once again, the pigeons made many anticipatory errors just
prior to the reversal and many perseverative errors after the
reversal. Another hypothesis for the pigeons’ poor performance with this task was that a component of the key-peck
response remained under the control of time into the session or
trial number. To determine whether the key-pecking response
was responsible for the pigeons’ inability to use the prior
response and its outcome as the basis for choice, Stagner,
Michler, Rayburn-Reeves, Laude, and Zentall (2013) had the
pigeons use a spatial treadle response rather than the key-peck
response that had been used earlier. Once again, the pigeons
were relatively insensitive to the change in contingency.
Recently, Rayburn-Reeves et al. (2013) proposed that the
reversal task for pigeons involved memory for the response
made on the previous trial and the outcome of that response,
maintained in memory over the 5-s intertrial interval that had
been used in previous research. They suggested that the task
could be thought of as a biconditional discrimination in which
a 5-s delay had been inserted between the sample stimulus
(consisting of the stimulus chosen and the outcome of that
response) and the comparison stimuli (the stimuli presented on
the following trial). If the intertrial interval was at least partially responsible for the errors around the reversal, RayburnReeves, Laude, and Zentall suggested that manipulation of the
duration of the intertrial interval might affect the error rate
before and after the reversal. Consistent with this hypothesis,
they found that in a spatial version of the midsession reversal
task, when the intertrial interval was 5 or 10 s, the pigeons
were less sensitive to the reversal, whereas when the intertrial
interval was only 1.5 s, near-optimal choice was found. That
is, the pigeons appeared to be using their recent reinforcement
history, as opposed to or in addition to the time or number of
trials into the session, as a cue to reverse their choice. RayburnReeves, Laude, and Zentall concluded that when the intertrial
interval was sufficiently short, the pigeons were able to use
their memory for the previous response as well as the outcome
of that response as the basis for the choice on the current trial,
42
and that this pattern of responding approximated a win–stay/
lose–shift strategy.
However, the improved performance that resulted from the
spatial discrimination with very short intertrial intervals also
may have resulted from a repetitive response pattern involving
the S1 location and the feeder (e.g., peck left, eat, peck left,
eat, peck left, eat,...) that was interrupted by the omission of
reinforcement on Trial 41 (i.e., the first trial on which choice
of S1 was no longer reinforced). When the intertrial interval
was 5 s, the reason that the pigeons’ accuracy on the spatial
midsession reversal was so poor may have been because the
time between trials was sufficient for the pigeons to engage in
interfering behavior (i.e., behaviors other than the correct
response based on the feedback from the last trial).
The purpose of the present experiment was to test the
repetitive-response-pattern hypothesis by replicating the
intertrial-interval manipulation used by Rayburn-Reeves et al.
(2013) using a visual (color) midsession reversal task. In the
present experiment, pigeons were trained on a midsession
reversal involving either a spatial or a color discrimination
and either a 1.5-s or a 5.0-s intertrial interval. If poor memory
for the stimulus to which a response had been made on the
preceding trial and the outcome of that response was responsible for the large number of anticipatory and perseverative errors
when the intertrial interval was 5.0 s, then we should see fewer
errors with both the spatial and color discriminations when the
intertrial interval was short (i.e., 1.5 s) than when it was long
(i.e., 5 s). On the other hand, if the improved performance with
the short 1.5-s intertrial interval found by Rayburn-Reeves,
Laude, and Zentall was due to the repetitive response pattern,
then the short intertrial interval should reduce errors in the
spatial task but not in the other three conditions. This outcome
would be predicted because in the color discrimination task, the
location of the correct response requires that the pigeon track
the positive discriminative stimulus, which can appear on either
the left or the right response key from trial to trial. That is, no
repetitive response pattern would be possible, as it is in the
spatial version of the task.
Method
Subjects
A total of 16 unsexed White Carneaux pigeons (ages 3–12 years)
purchased from the Palmetto Pigeon Plant, Sumter, South
Carolina, served as subjects. All of the pigeons had had experience with successive color discriminations, but not with simultaneous discriminations or with a reversal-learning task. The
subjects were maintained at 85 % of their free-feeding weight
and were individually housed in wire cages with free access to
water and grit in a colony room that was maintained on a 12-h/
Learn Behav (2014) 42:40–46
12-h light/dark cycle. The pigeons were cared for in accordance with University of Kentucky animal care guidelines.
Apparatus
The experiment took place in a BRS/LVE (Laurel, MD)
standard sound-attenuating operant test chamber measuring
34 cm high, 30 cm wide, and 35 cm across the response
panel. Three circular response keys (2.54-cm diameter) were
horizontally aligned on the response panel (spaced 6.0 cm apart
from edge to edge) and were located 25 cm from the floor. A 12stimulus in-line projector (Industrial Electronics Engineering,
Van Nuys, CA) with 28-V, 0.1-A lamps (GE 1820) was
mounted behind the left and right response keys to project
green and red hues (Kodak Wratten Filter Nos. 2 and 60,
respectively). Reinforcement consisted of 1.5-s access to
mixed grain (Purina Pro Grains, a mixture of corn, wheat,
peas, kaffir, and vetch) that was provided from a food hopper.
A 28-V, 0.04-A lamp illuminated the hopper when reinforcement was delivered. Experimental events were controlled by a
microcomputer and interface located in an adjacent room.
Procedure
Subjects were randomly assigned to one of four conditions
(n = 4 in each group) that varied in the duration of the intertrial
interval (ITI; 1.5 or 5.0 s) and the discrimination type (visual or
spatial): Group 1.5–Spatial, Group 5–Spatial, Group 1.5–Visual,
and Group 5–Visual.
For subjects assigned to the spatial versions of the task, at
the start of each trial, both the left and right response keys
were illuminated, for example, green (for the other half of the
subjects, red key lights were used). For half of the subjects, a
single peck to the left side key (i.e., the first correct stimulus,
or S1) turned off both key lights, started the ITI (1.5 s for
pigeons in Group 1.5–Spatial, and 5.0 s for pigeons in Group
5–Spatial), and provided reinforcement consisting of 1.5-s
access to mixed grain. A response to the right key (i.e., the
second correct stimulus, or S2) turned off both keys and
resulted in the ITI alone. For the other half of the pigeons,
initial choice of the right key (S1) was reinforced, and the left
key (S2) was not. For the first 40 trials of each 80-trial session,
the subjects were trained with S1+/S2−. On Trial 41 a reversal
occurred, such that for Trials 41–80, choice of the previously
nonreinforced spatial location was reinforced (S2+/S1−).
Pigeons assigned to the visual version of the task were
presented with red and green hues, illuminated on the left
and right response keys. The positive discriminative stimulus
(S1) appeared randomly on either the left or the right key from
trial to trial. For half of the subjects, a response to the red key
(S1) turned off both keys, started the ITI (1.5 s for pigeons in
Group 1.5–Visual, and 5.0 s for pigeons in Group 5–Visual),
and provided reinforcement consisting of 1.5-s access to
Learn Behav (2014) 42:40–46
43
mixed grain. Responding to green (S2) turned off both
keys and resulted in the ITI alone. For the other half of the
subjects, choice of the green key (S1), not the red key (S2),
was initially reinforced. For the first 40 trials of each 80-trial
session, subjects were trained with S1+/S2−, and on Trial 41 a
reversal occurred, such that for Trials 41–80, the previously
nonreinforced color was reinforced (S2+/S1−). All subjects
were trained for 60 sessions.
None of the other terms in the model was statistically significant (all ps > .25). Minimal improvements in task accuracy
were observed over the subsequent 30 sessions. When the data
were pooled over the last 20 sessions, a one-way ANOVA
revealed that terminal, overall performance was not significantly different as a function of condition: Group 1.5–Spatial,
M = 94.1, SE = 1.42; Group 1.5–Visual, M = 88.0, SE = 2.47;
Group 5–Visual, M = 89.5, SE = 1.68; and Group 5–Spatial,
M = 89.4, SE = 0.89; F(3, 12) = 2.44, p = .11.
Results
Sensitivity to the reversal
Acquisition
The percentage of choices of the first correct stimulus (S1) as a
function of trial number (in blocks of five trials) averaged over
subjects for the last 20 training sessions (Sessions 41–60) can
be found in Fig. 2. As can be seen in the figure, Group 1.5–
Spatial appears to have greater sensitivity to the reversal, whereas the other three groups show considerably less sensitivity to
the change in contingency. On the other hand, the four groups
do show comparable degrees of insensitivity to the reversal.
In line with our previous research (Rayburn-Reeves et al.,
2013, 2011), in approximately 20–30 sessions, the discrimination reversals were acquired to a level at which accuracy
changed little with continued training. The pigeons in both
spatial groups acquired the midsession reversals very quickly,
whereas the pigeons in the two visual groups were slower to
acquire the midsession reversals. In fact, from the first session
of training, pigeons in the two spatial groups performed the
midsession reversal at better than 90 % correct. To compare the
rates of acquisition among the four groups, a three-factor
mixed-model analysis of variance (ANOVA) was conducted
on the total percentages of choices correct for each session with
ITI Duration (1.5 or 5.0 s) and Task Type (visual or spatial) as
between-subjects factors, with repeated measures on the third
factor, Session (1–30). The analysis indicated a main effect of
session, indicative of an increase in overall accuracy with
training, F(29, 348) = 3.39, p < .001. We also observed a main
effect of task type, F(1, 12) = 16.97, p = .001, which was
qualified by a significant Task Type × Session interaction,
F(29, 348) = 2.83, p < .0001, indicating that the spatial task
was acquired at a faster rate than the visual task (see Fig. 1).
Trial-by-trial analysis
To more closely examine each group of pigeons’ sensitivity to
the reversal, we examined the trial-by-trial accuracy of each
group on the trials immediately before and after the reversal
(see Fig. 3). As can be seen in Fig. 3, the pigeons in the spatial
groups made fewer anticipatory errors than did the pigeons in
the visual groups, and the pigeons in the 1.5-s groups made
somewhat fewer anticipatory errors than did the pigeons in the
5.0-s groups; however, the groups did not appear to differ in
the numbers of perseverative errors made. To determine
whether the groups differed in their sensitivity to the feedback
from the reversal, a one-way ANOVA was conducted on the
difference between the average of the percentage choices of
Fig. 1 Acquisition (Sessions 1–30) by pigeons of a spatial midsession reversal with a 5.0-s ITI (Group 5–Spatial) or a 1.5-s ITI (Group 1.5–Spatial), or
of a visual (color) midsession reversal with a 5.0-s ITI (Group 5–Visual) or a 1.5-s ITI (Group 1.5–Visual)
44
Learn Behav (2014) 42:40–46
Fig. 2 Asymptotic choice of the stimulus that was correct on the first 40
trials of each session plotted in blocks of five trials for pigeons trained on
a spatial midsession reversal with a 5.0-s ITIs (Group 5–Spatial), or a
1.5-s ITIs(Group 1.5–Spatial) and for pigeons trained on a visual (color)
midsession reversal with a 5.0-s ITIs (Group 5–Visual), or a 1.5-s ITIs
(Group 1.5–Visual)
the first correct stimulus (S1) on Trials 37–41 (the five trials
that occurred just prior to the feedback from the first reversal
trial) and on Trials 42–46 (the first five trials following the
reversal), involving the data from all four conditions. The
analysis indicated an overall effect of condition, F(3, 12) =
10.61, p = .001. A planned comparison was then conducted
comparing the sensitivity to the reversal (the difference
between the averages of the percentages of choices of
the first correct stimulus (S1) on Trials 37–41 and Trials
42–46) for Group 1.5–Spatial (M = 71.8, SE = 8.57) to
the other three groups: Group 1.5–Visual (M = 30.0, SE =
7.82), Group 5–Spatial (M = 42.2, SE = 4.75), and Group
5–Visual (M = 25.8, SE = 2.29). The analysis revealed
that pigeons in Group 1.5–Spatial were significantly more
sensitive to the change in contingency, F (1, 12) = 28.23,
p < .05 (see Fig. 3).
Fig. 3 Asymptotic choice of the stimulus that was correct on the first 40
trials of each session for the final five trials before and first five trials after
the reversal of each session (trial by trial for Trials 37–46) for pigeons
trained on a spatial midsession reversal with a 5.0-s ITIs (Group 5–
Spatial), or a 1.5-s ITIs (Group 1.5–Spatial) for pigeons trained on a
visual (color) midsession reversal with a 5.0-s ITIs (Group 5–Visual), and
or a 1.5-s ITIs (Group 1.5–Visual)
Learn Behav (2014) 42:40–46
A further planned comparison was conducted comparing
Group 5–Spatial with the two visual groups (Group 1.5–Visual
and Group 5–Visual). The analysis revealed that the difference
was not statistically significant, F(1, 12) = 3.39, p = .09. Finally,
a planned comparison was conducted comparing Group 1.5–
Visual with Group 5–Visual, and the analysis revealed that the
difference was not statistically significant, p > .05.
Discussion
Rayburn-Reeves et al. (2011) found that when pigeons were
trained on a color-discrimination midsession reversal with 5-s
ITIs, the subjects were relatively insensitive to the point of the
reversal. The results of the present study confirm the earlier
finding that when pigeons are trained on a midsession reversal
involving a visual (color) discrimination with an ITI of 5 s, the
reversal is guided largely by time or the number of trials into
the session, rather than by the local feedback cues resulting
from the stimulus and outcome from the last response made. In
later research, it was hypothesized that the reversal might be
made more salient if the discrimination was spatial (RayburnReeves et al., 2013), but only a small decline in anticipatory
errors was found. Rayburn-Reeves, Laude, and Zentall suggested that the task could be considered a biconditional discrimination, with the stimulus selected on a given trial and the
outcome of the choice serving as the biconditional sample and
the 5.0-s ITI serving as a delay between the offset of the sample
and the onset of the comparison stimuli. When viewed in this
way, the relatively poor accuracy prior to and following the
reversal could be attributed largely to the 5.0-s ITI (see,
e.g., Randall & Zentall, 1997). If this characterization is
correct, Rayburn-Reeves, Laude, and Zentall reasoned that
anticipatory and perseverative errors might be reduced by
shortening the ITI. In fact, when they shortened the ITI to
1.5 s, no evidence of systematic anticipatory errors emerged,
and perseverative errors were largely eliminated, as well.
In the present experiment, we manipulated the nature of the
task (spatial or visual) and the intertrial interval (1.5 or 5.0 s),
and we found that in line with our hypothesis, pigeons trained
with a 1.5-s ITI showed fewer errors around the reversal than did
the other three groups: Group 1.5–Visual, Group 5–Visual, and
Group 5–Spatial. Consistent with earlier research (RayburnReeves et al., 2013), pigeons trained on the spatial discrimination midsession reversal with short ITIs showed a pattern of
errors that approximated a win–stay/lose–shift strategy.
The results of the present experiment suggest that with the
visual-discrimination midsession reversal with relatively long
ITIs used by Rayburn-Reeves et al. (2011), poor memory for
the events from the preceding trial was largely responsible for
the reliance on time or number of trials into the session as a cue
to reverse (but see McMillan & Roberts, 2012, who found that
their pigeons showed evidence of timing when they increased
45
or decreased the ITI). The advantage of the spatial discrimination was that proprioceptive and kinesthetic cues provided by
pecking the key and moving from the key to the feeder provided
relevant cues that, together with the outcome of the choice, were
sufficient to guide choice on the following trial. Furthermore,
the shorter ITI greatly reduced the memory load for the events
from the previous trial. This suggests that when the
difficulty of the biconditional discrimination is increased by
adding time between the events that cue future reinforcement,
pigeons tend to rely more heavily on the passage of time or the
number of trials within the session, which influence the pigeon’s choice more than the cues from the preceding trial.
Although the conditions in which pigeons continue to
make errors around the reversal could have involved the use
of either time or trials into the session as a cue to estimate the
reversal point, the results reported by Rayburn-Reeves et al.
(2013) suggest that estimation of trial number was the more
likely cue. In their study, they found that manipulation of the
ITI resulted in near-identical anticipatory and perseverative
error rates among pigeons that had 5.0-s ITIs and 10.0-s ITIs.
Had the pigeons been using time into the session as a cue to
reverse, one would have expected timing to the middle of the
session to have been somewhat poorer when the ITI was 10 s
than when it was only 5 s; however, estimation of the number
of trials into the session would be expected to be about the
same in both conditions.
When Rayburn-Reeves et al. (2011) reported that pigeons are
relatively insensitive to the local cues provided in the midsession
reversal, they focused on the presumed simplicity of the simultaneous visual discrimination, and failed to consider the contribution of the 5.0-s ITI. When, in the present experiment, we
simplified the discrimination by making it spatial and shortened
the ITI from 5.0 s to 1.5 s, performance on the midsession
reversal approached ideal win–stay/lose–shift performance.
It is interesting to note that rats trained on a spatial discrimination midsession reversal have shown virtually no anticipatory errors, even when the ITI was relatively long (5.0 s). The
difference between rats and pigeons on this version of the task
may be related to inherent differences in the abilities of the
animals to benefit from experience with tasks involving multiple reversals (serial reversal tasks; see Bitterman, 1975), but
it is also possible that differences in the ways that the two
species make their responses contribute to the differences
found. Pigeons must peck and eat with their beaks. Thus, they
must move their head away from the key when they eat, and
the 5.0-s ITI introduces a memory load for the response key
last pecked. Rats, on the other hand, press the lever with their
paw and can maintain contact with the lever (or stay in close
proximity to it) when they eat from the magazine. Thus, the
spatial location of their paw between trials can serve as a
salient cue for the next response 5.0 s later, and at the point
of the reversal (Trial 41), the absence of reinforcement serves
as a salient cue to press the other lever. For the pigeons, the
46
short, 1.5-s ITI reduces the memory load and allows for a
continuous sequence of key-peck, consummatory response,
and back to the pecking key for the pigeon, disrupted only by
the absence of reinforcement on Trial 41. Thus, the combination of a spatial midsession reversal together with a short ITI
allowed the pigeons to show a near win–stay/lose–shift reversal pattern.
With the short, 1.5-s ITI, the pigeons should have had
little difficulty remembering both the color of the stimulus
pecked from the preceding trial and the outcome of that
choice. The fact that they could not do so efficiently with
the visual discrimination reversals suggests that the repetitive response pattern involving the S1 location and the
feeder was what allowed the pigeons to overcome their
tendency to use the time into the session or an estimate of
the number of trials experienced as a cue to begin to reverse, even though that pattern of choice was not as efficient as the more optimal win–stay/lose–shift response pattern. Thus pigeons’ performance on the repeated midsession
reversal continues to present animal learning researchers with
a curious pattern of responding.
Author note This research was supported by National Institute of Child
Health and Development Grant No. 60996.
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