Memorization of serial items by Japanese monkeys, a chimpanzee, and humans

The memorization of serial items was investigated with three Japanese monkeys, a chimpanzee, and six humans. The subjects were trained to touch two to four different-sized circles in an order determined by the experimenter Two types of list were presented: monotonic and nonmonotonic. The subjects performed better with monotonic than with nonmonotonic lists, both in terms of the percentage of correct trials and reaction times, The subjects' search strategies were classified as either a serial search or a collective search. The chimpanzee more often used a collective search than a serial search, compared with the Japanese monkeys. This tendency was also prevalent with the human subjects. Therefore, a collective search might be an evolutionarily new cognitive function. A serial search model based on evaluation and motion is proposed, and this could well explain the subjects' reaction times.