| Abstract |
In natural environments, the outcomes of actions are often delayed and separated from the actions themselves by intervening events, posing a credit assignment problem for learning. Although both humans and nonhuman animals can associate actions with immediate subsequent outcomes, little is known about learning when action-outcome delays span multiple, unpredictably ordered events. We investigated whether chimpanzees could associate a choice with a reward delivered several trials later, using a touchscreen-based task. Six chimpanzees completed four experimental rounds involving three trial types: an immediately rewarded discrimination, a non-rewarded choice that triggered a delayed reward, and a reward-delivery trial contingent solely on prior choices. Three chimpanzees showed a significant increase in choosing the stimulus associated with delayed reward. Reversal of stimulus roles in a later round confirmed that increased selection of the delayed-reward stimulus was not attributable to fixed stimulus preferences. Although performance remained variable across individuals and sessions, the results suggest that chimpanzees possess learning mechanisms capable of bridging extended action-outcome gaps, likely operating implicitly rather than through explicit understanding of task structure. Our study contributes to comparative perspectives on the evolutionary origins of learning beyond the "here and now."
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