American Psychological Association, Inc. Monkey Memory: Same I Different Concept Learning, Serial Probe Acquisition, and Probe Delay Effects

Three rhesus monkeys were trained and tested in a same/different task with six successive sets of 70 item pairs to an 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 four 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. These results are compared with similar ones from pigeons and are discussed in relation to theories of memory processing. The primacy effect, good memory of the first list items, has been recently demonstrated for two monkey species (Roberts & Kraemer, 1981; Sands & Wright, 1980a, 1980b) and a chimpanzee (Buchanan, Gill, & Braggio, 1981). The rinding of animal primacy effects, as well as the more common recency effects (remembering the last list items well) is im-portant because it demonstrates the continuity between human and nonhuman primate memory processing. Prior to the discovery of a nonhuman primate primacy effect, serial-position functions for monkeys revealed onl