Michael J. Beran, Ph.D.
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Last updated: 
June 11, 2022



Beran, M. J., Smith, J. D., Redford, J. S., & Washburn, D. A. (2006). Rhesus macaques (Macaca mulatta) monitor uncertainty during numerosity judgments. Journal of Experimental Psychology: Animal Behavior Processes, 32, 111-119.

Two rhesus macaques (Macaca mulatta) judged arrays of dots on a computer screen as having more or fewer dots than a center value that was never presented in trials. After learning a center value, monkeys were given an uncertainty response that let them decline to make the numerosity judgment on that trial. Across center values (3-7), errors occurred most often for sets adjacent in numerosity to the center value. The monkeys also used the uncertainty response most frequently on these difficult trials. A second experiment showed that monkeys’ responses reflected numerical magnitude and not the surface-area illumination of the displays. This research shows that monkeys’ uncertainty-monitoring capacity extends to the domain of numerical cognition.  It also shows monkeys’ use of the purest uncertainty response possible, uncontaminated by any secondary motivator.

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