A reversed-reward contingency task reveals causal knowledge in chimpanzees (Pan troglodytes)
In the reversed-reward contingency task, subjects are required to choose the less preferred of two options in order to obtain the more preferred one. Usually, this task is used to measure inhibitory skills, but it could also be used to measure how strong the subjects’ preferences are. We presented chimpanzees with support tasks where only one of two paper strips could physically bring food into reach. Subjects were rewarded for choosing the non-functional strip. In Experiment 1, subjects failed to pick the non-baited strip. In Experiment 2, subjects failed to pick the broken strip. Chimpanzees performed worse in these tasks than in other similar tasks where instead of paper strips, there were similar shapes painted on a platform. The fact that subjects found the reversed-reward contingency task based on causality more difficult to solve than a perceptually similar task with no causality involved (i.e., arbitrary) suggests that they did not treat real strips as an arbitrary task. Instead, they must have had some causal knowledge of the support problem that made them prefer functional over non-functional strips despite the contrary reward regime.
KeywordsReversed-reward contingency Inhibition Support Causal knowledge Chimpanzees
We would like to thank the keepers of Pongoland, in Leipzig Zoo, for providing help with the chimpanzees. Also, we are grateful to James Close for the proof reading of this article. Finally, we acknowledge the comments of two anonymous reviewers on a previous version of this manuscript.
Conflict of interest
The authors declare that they have no conflict of interest.
This study strictly adhered to the legal requirements of the country in which it was conducted.
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