Monkey memory: Same/different concept learning, serial probe acquisition, and probe delay effects.

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Abstract
Three rhesus monkeys were trained and tested in a same/different task with 6 successive sets of 70 item pairs to 88% accuracy on each set. Their poor initial transfer performance (55%) correct with novel stimuli improved dramatically to 85% correct following daily item changes in the training stimuli. They acquired a serial-probe-recognition (SPR) task with variable (1-6) item list lengths. This SPR acquisition, although gradual, was more rapid for the monkeys than for pigeons similarly trained. Testing with a fixed list length of 4 items at different delays between the last list item and the probe test item revealed changes in the serial-position function: a recency effect (last items remembered well) for 0-s delay, recency and primacy effects (first and last list items remembered well) for 1-, 2- and 10-s delays, and only a primacy effect for the longest 30-s delay. Results are compared with similar ones from pigeons and are discussed in relation to theories of memory processing.