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Gorillas’ use of the escape response in object choice memory tests

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The ability to monitor and control one’s own cognitive states, metacognition, is crucial for effective learning and problem solving. Although the literature on animal metacognition has grown considerably during last 15 years, there have been few studies examining whether great apes share such introspective abilities with humans. Here, we tested whether four gorillas could meet two criteria of animal metacognition, the increase in escape responses as a function of task difficulty and the chosen-forced performance advantage. During testing, the subjects participated in a series of object choice memory tests in which a preferable reward (two grapes) was placed under one of two or three blue cups. The apes were required to correctly select the baited blue cup in this primary test. Importantly, the subjects also had an escape response (a yellow cup), where they could obtain a secure but smaller reward (one grape) without taking the memory test. Although the gorillas received a relatively small number of trials and thus experienced little training, three gorillas significantly declined the memory tests more often in difficult trials (e.g., when the location of the preferred reward conflicted with side bias) than in easy trials (e.g., when there was no such conflict). Moreover, even when objective cues were eliminated that corresponded to task difficulty, one of the successful gorillas showed evidence suggestive of improved memory performance with the help of escape response by selectively avoiding trials in which he would be likely to err before the memory test actually proceeded. Together, these findings demonstrate that at least some gorillas may be able to make optimal choices on the basis of their own memory trace strength about the location of the preferred reward.

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I thank Lisa Stevens for allowing me to work with the great apes at the Smithsonian’s National Zoological Park and all the zookeepers of the Great Ape House for their support. I also thank Milton Tierney for constructing the testing apparatus. This study was supported by a research grant from the David Bohnett Foundation, the Smithsonian Institute Fellowship to CK, and a CAREER Grant from the National Science Foundation to FS (BCS-0748717). All of the experiments were approved by the IACUC of the National Zoological Park and complied with the current laws of the country in which they were conducted.

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Correspondence to Chikako Suda-King.

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Suda-King, C., Bania, A.E., Stromberg, E.E. et al. Gorillas’ use of the escape response in object choice memory tests. Anim Cogn 16, 65–84 (2013).

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