Michael J. Beran, Ph.D.
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September 1, 2021



Beran, M. J. (2007). Rhesus monkeys (Macaca mulatta) enumerate large and small sequentially presented sets of items using analog numerical representations. Journal of Experimental Psychology: Animal Behavior Processes, 33, 42-54.

Two rhesus monkeys selected the larger of two sequentially presented sets of items on a computer monitor. In Experiment 1, performance was related to the ratio of set sizes, and the monkeys discriminated between sets with up to 10 items. Performance was not disrupted when one set had fewer than 4 items and one set had more than 4 items, a critical trial type for differentiating object file and analog models of numerical representation. Experiment 2 controlled the inter-item rate of presentation. Experiment 3 included some trials in which number and amount (visual surface area) offered conflicting cues. Experiment 4 varied the total duration of set presentation and the duration of item visibility. In all of these experiments, performance remained high, although total set presentation duration also acted as a partial cue for the monkeys. Overall, the data indicated that rhesus monkeys estimate the approximate number of items in sequentially presented sets, and they are not relying solely on nonnumerical cues such as rate, duration, or cumulative amount.

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