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Do zoo visitors induce attentional bias effects in primates completing cognitive tasks?

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While previous research has focused on the impact of visitors on zoo-housed animals’ behavior, here, we evaluated the impact of visitors on the performance of four zoo-housed Japanese macaques (Macaca fuscata) in a cognitive task. The macaques completed a touchscreen-based match-to-sample task in glass-sided booths at the perimeter of their enclosure, adjacent to a visitor viewing area. The task was novel to all macaques at the start of this study but over the 6-month testing period the macaques showed increased accuracy on the task, suggestive of learning. We recorded the number of visitors within the viewing area roughly every 12 trials each macaque completed. We categorized visitor counts as small (0–20), medium (21–40), and large (41–60) crowds and we considered the macaques’ response latencies and accuracy by crowd size and study period (first 3 months versus second 3 months). If visitor presence negatively influenced performance, we predicted that macaques’ accuracy would decrease but response times would increase with crowd size. We found effects of crowd size and study period on the macaques’ accuracy. In the first period, the macaques performed at chance and accuracy did not differ across crowd categories. In the second period, the macaques’ accuracy improved as compared to the first period, but their accuracy was mediated by crowd size: the macaques were significantly more accurate in the presence of small crowds than medium or large crowds. The macaques’ response latencies also varied by study period and crowd size, but we found no evidence of a response-slowing effect.

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The authors would like to thank the animal care staff at Lincoln Park Zoo’s Regenstein Macaque Forest for the daily care for our subjects and for being supportive of our research, in particular Jill Moyse and Danielle Fogarty. We also greatly appreciate the helpful feedback offered to us by three anonymous reviewers on an earlier version of this article. We also thank the Lincoln Park Zoo Women’s Board for funding this research.


The Lincoln Park Zoo Women’s Board.

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Authors and Affiliations



SMH: Methodology, investigation, data curation, formal analysis, visualization, writing—original draft, writing—review and editing; SRR: Funding acquisition, resources, supervision, writing—review and editing; and LMH: Conceptualization, methodology, data curation, formal analysis, funding acquisition, project administration, resources, supervision, writing—review and editing.

Corresponding author

Correspondence to Lydia M. Hopper.

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The author declares that they have no conflicts of interest.

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This study was approved by Lincoln Park Zoo’s Research Committee and was conducted in accordance with the American Society of Primatologists’ Principles for the Ethical Treatment of Nonhuman Primates.

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We affirm that the research described here has not been submitted or published in another venue, and all authors are aware of the manuscript’s submission to this journal.

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Huskisson, S.M., Ross, S.R. & Hopper, L.M. Do zoo visitors induce attentional bias effects in primates completing cognitive tasks?. Anim Cogn 24, 645–653 (2021).

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