Externalizing forgetting: delay testing in a long operant chamber

Abstract

In a long operant chamber, pigeons were trained to discriminate between 4-s and 12-s samples in a symbolic matching-to-sample task. Subsequently, delay and no-sample test trials were introduced. The location in the chamber in which the trial started and each comparison was presented varied across three experiments. Our main goals were to assess the effect of the delay and to compare preferences on delayed and no-sample trials. Both pigeons' preferences and their movement patterns were analyzed. In Experiments 1 and 3, pigeons learned to move immediately to the location where the correct comparison would be presented, allowing them to select a comparison at its onset and receive reinforcement. In Experiment 2, some birds moved differently-probably reflecting an interaction of travel distance with outcome certainty. On delay testing, as the delay increased, accuracy decreased and the pigeons tended to move to the middle of the chamber, irrespective if that location was associated with the beginning of the trials or with one of the comparisons. Inserting a delay seemed 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. On no-sample delayed testing, pigeons also showed a tendency to move toward the middle of the chamber, which was combined with a preference for the comparison associated with the short sample.