Michael J. Beran, Ph.D.
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Last updated: 
September 1, 2021

 

 

Beran, M. J., & Beran, M. M. (2004). Chimpanzees remember the results of one-by-one addition of food items to sets over extended time periods. Psychological Science, 15, 94-99.

Four chimpanzees were highly accurate in selecting the larger of two concurrent accumulations of bananas in two opaque containers over a span of 20 minutes. Bananas were placed, one at a time, into one of the two opaque containers outside of the chimpanzeesí cages. The chimpanzees never saw more than one banana at a time, and there were no cues indicating the locations of the bananas after they were placed into the containers. The performance of these animals matched that of human infants and children up to four years of age in similar tests. The chimpanzees were successful even when the sets to be compared were sufficiently large (5 versus 8, 5 versus 10, and 6 versus 10) to discount the possibility that the chimpanzees were using an object file mechanism. The chimpanzees provided the first demonstration by nonhuman animals of extended memory for accumulated quantity.

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