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In Experiment 1, three groups of pigeons were trained in
delayed matching-to-sample procedures to investigate the effects
of successive responses to a pair of sample or comparison stimuli
as compared to responses to a single key. The group that was
required to respond sequentially both to the sample and
comparison stimuli (Group SEQ-SEQ) was the slowest to reach
the criterion. Group SEQ-SG, which was required to respond
sequentially only to the samples reached criterion faster and
performed better when much longer delay intervals were
introduced. In Experiment 2, Group SEQ-SG was further analyzed
to determine which contributed to its performance, the
sequentiality or the number of responses to the sample. The
results showed that the latter was more effective, consistent with
prior reports that accuracy on delayed matching-to-sample
increases as the number of responses to the sample increases.