Processing of identity and conditional relations in monkeys (Cebus apella) and pigeons (Columba livid)

As a test of differential processing of identity and conditional relations, subjects were first highly trained on 0-sec delay identity matching (IM) and conditional (“symbolic”) matching (CM), with the same pair of stimuli serving as samples in both tasks. CM probe trials were then randomly interspersed among baseline IM trials and vice versa. The differences in response latencies obtained on the probe and baseline trials provided the critical data. It was argued that differential processing of identity and conditional relations should result in a larger difference in response latency when CM probes were interspersed among IM baseline trials than when the reverse assignment was made. This pattern was found in cebus monkeys but not in pigeons. The results provide further evidence for the matching concept in monkeys, and they support the view that the matching concept is at best only weakly represented in pigeons.