20º Encontro APPE

Externalizing Forgetting: Delay Testing in a Long Operant Chamber

To study animals’ ability to behave according to time-related cues (i.e., perform temporal discriminations), the symbolic matching-to-sample task has been widely used. In this task, animals choose between two options (i.e., the comparisons) according to the duration of a previously presented stimulus (i.e., the sample). A variation of this task in which a delay is introduced between the sample and the comparisons—the delayed symbolic matching-to-sample—has been extensively used to study animal memory given that to respond correctly animals need to retain information during the delay. Yet, choice biases have been reported and, while some authors attributed them to a memory-related process, others do not. To clarify the effects of inserting a delay following a temporal discrimination, we conducted a series of experiments with pigeons in a long operant chamber. This chamber allows bridging hypothetical internal events, for instance, temporal estimation and sample memories, to external events, pigeons’ movements. The location where trials started and where each comparison was presented varied across experiments. Results showed that as the delay increased, accuracy decreased and pigeons tended to move toward the middle of the chamber, irrespective of what that location was associated with. Inserting a delay seems to lead to a disruption where stimulus control by the sample was reduced and replaced by control by the location at the moment of choice. To test whether this disruption resulted from the novelty of the delay, two additional experiments were conducted in which the delay was present since the beginning and, its duration was simply decreased or increased during testing. Results remained similar which is not consistent with the novelty hypothesis.