Abstract # 2854 Event # 125:

Scheduled for Saturday, June 19, 2010 09:30 AM-09:40 AM: Session 20 (Medallion Ballroom B) Oral Presentation


CHIMPANZEES (PAN TROGLODYTES) DELAY GRATIFICATION BY ACCEPTING TOKENS IN LIEU OF REWARDS

T. A. Evans, M. J. Beran and D. Hoyle
Georgia State University, Language Research Center, Decatur, GA, USA
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Tokens inherently introduce an element of delay between behavior and reward. For this reason, token studies may help us understand how animals process delays and anticipate future events. We presented 4 chimpanzees with tests involving choices between different numbers of visible food treats and tokens that could be later exchanged for similar treats, one-to-one. When we allowed chimpanzees to exchange tokens for rewards after each trial, they often chose a larger set of tokens over a smaller set of immediately available food items [Mean: 39%, Range: 15-70%]. Next, when chimpanzees had to complete 8 trials before exchanging tokens but could eat food items immediately, they preferred the smaller, immediate rewards [Binomial Tests: all P's< 0.001]. However, when we also delayed the delivery of visible food items, the chimpanzees selected the larger number of tokens more often [Mean: 74%] than in the previous experiment [Mean: 39%]. Finally, when we presented chimpanzees with repeated choices between two different token amounts and allowed them to exchange tokens for rewards only once at the end of each session, they quickly learned to collect a number of tokens before choosing to exchange [Mean: 14 tokens, Range 2-50 tokens]. Therefore, chimpanzees delayed gratification by selecting and holding tokens, and sometimes did so even when visible food items were present. Research supported by NSF Grant BCS-0924811.