Studies with pigeons have shown that releasing reinforcers during the Intertrial Interval (ITI)
on simple and conditional discrimination tasks can produce a drop on the stimulus control. In
the case of conditional discrimination, the literature suggests that the conditions that
deteriorate the performance involve the reinforcer’s release at the end or during all the ITI, in
other words, when the reinforcer is released next to the beginning of a new trial. This study
had the objective to investigate the effects of releasing of reinforcers during the ITI on the
performance on the identity delayed-matching-to-sample task (DMTS) with three capuchin
monkeys (Sapajus spp.). Each trial was initiated by presenting a sample stimulus; after the
emission of five touches to the sample, it was initiated a delay and, at the end of the delay,
comparison stimuli were presented so the choice response would occur. Correct responses
were followed by the release of 190 mg banana’s pellet and by the ITI and incorrect responses
were followed just by the ITI. The sessions were composed by trials with 1 s, 5 s, and 20 s
delay and 30 s ITI. In order to study the effects of free reinforcer releasing , a 190 mg pellet
was released also during the ITI, according to five conditions, which sequence was random
and differed between subjetcs: Early – free reinforcer released 5 s after the beginning of the
ITI; Middle – release 15 s after the beginning of the ITI; Late – release 25 s after the
beginning of the ITI; All – release 5 s, 15 s and 25 s after the beginning of the ITI; and, None
– there was no reinforcement release during the ITI. These conditions were applied in two
procedures. On the first, named Maintenance, just one set of stimuli was used on all
conditions of manipulation of reinforcement; on the second, named Acquisition, each
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condition presented a specific stimulus set. No effect of different conditions of free reinforcer
releasing was observed on the general performance of the subjects. However, on the
Acquisition procedure, it was verified a decay on the performance on the trials with maximum
delay, 20 s, though the conditions of releasing reinforcement that affected the performance at
these trials were different between the subjects. The result of one of the three subjects was
similar to what was found on the literature, the deterioration on the performance on the trials
with the longest delay, 20 s, occurred on the conditions in which the reinforcement was
released at the end or during all the ITI. The other participants showed decay on the
conditions in which there was no reinforcement during the ITI or when the release occurred at
the beginning or end of the ITI. We suggest, for future researches, to test the same
performances under the same conditions with new sets of stimuli seeking intra-subject
replication and later to use trials with delays longer than the 20 s, according to the training
history in different delays of each subject.
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