Concerning memory in the chimpanzee

With three objectives, namely (1) to observe the character of the delayed response in a controlled complex situation, (2) to determine the temporal limits of delay (memory span), and (3) to discover whether or not the delayed response is dependent upon merely one sensory factor, viz., color, in a varying situation, an experiment was conducted on four immature West African chimpanzees aged from four to seven and one-half years. A duplicate of the author's Florida gorilla apparatus was used. The animals, after a delay of three hours, can immediately and with ease gain access to the food box or the place where food has been placed; this is effected through position habits or spatial cues. When, however, position was made variable and the color of the food box constant, the animals exhibited much greater difficulty, the maximum period of delay being reduced to approximately 30 minutes. In the latter case their behavior became characterized by observational scrutiny, comparison, frequent recognition, hesitation, delay, occasional vacillation, disappointment, incredulity, mystification, resentment, anger, depression, and sometimes refusal to choose. Supplementary experiments, involving the chimpanzee's memory for persons and his finding buried food, indicate a memory carryover for a period of 10 months in the former and 96 hours in the latter. The animals did not fall into the same rank order for the three experiments and great individual differences characterized the fixed-color, variable-position experiment. The work is being continued. One figure, three tables, and six references.