Simultaneous and delayed physical identity matching -to -sample: Acquisition and transfer of responding to nominal categories of photographic stimuli by rhesus monkeys (Macaca mulatta)

Four monkeys were trained on an identity matching-to-sample task then transferred to novel stimuli under three delay conditions: simultaneous, single delay within a session, and multiple delays within a session to examine the effects of delay on acquisition and transfer of the identity matching. Five sets of digitized color photographs of natural objects, each divided into eight categories (amphibians, birds, fish, flowers, fruits and vegetables, insects, mammal faces and shells) were used. In Experiment 1 monkeys were trained on a simultaneous MTS task and performed significantly above chance when presented with novel stimuli. The delay between sample and comparison stimuli was gradually increased across sessions in Experiment 2, and the monkeys again were able to perform significantly above chance and no different from familiar stimuli when presented with novel stimuli. Finally, in Experiment 3, delays ranging from 8s to 80s in 8s increments were presented randomly from trial to trial. Though performance on novel stimuli was above chance, accuracy was significantly lower for novel stimuli than for familiar stimuli. Accuracy also decreased as the delay increased. Performance on trials with sample and distractor items from the same category did not differ significantly from performance on trials with the sample and distractor from different categories except during transfer to novel stimuli while the delay varied within a session. The monkeys learned an identity match when trained on photographic stimuli that transferred to novel stimuli without regard for category.