We are interested in counting and arithmetic skills in nonhuman primates, human adults, and human children. With regard to the question of whether animals are capable of counting behavior, we have approached the question through use of computerized tests of what is called constructive enumeration.

In these tests, chimpanzees have learned to select items on a computer screen, one-at-a-time, until they have accumulated (or constructed) a set equal to a presented target numeral. Chimpanzees are successful on such tasks for numerals up to 8, but performance is indicative of a process more similar to estimation than to formal counting.

The chimpanzees show decreasing performance levels as a function of increasing set size, and they also show greater variability in the size of the constructed set as numeral values increase. This pattern indicates that the enumerative process used by the animals is approximate in its representation of set size.

We have assessed estimation skills in chimpanzees, monkeys, human adults, and human children. In these tests, participants observe as items are placed into and removed from opaque containers so that additive and subtractive operations can be presented. This sequential presentation method has produced compelling similarities in the performance of the nonhuman primates and human children. In addition, recent studies have indicated that articulatory suppression methods can block subvocal counting routines in adult humans, producing data sets that are very similar to those of nonhuman primates and children who have not yet mastered the counting routine. Thus, these comparative data strongly suggest a shared mechanism for the approximate representation of set size for sequentially presented arrays. Modifications of the testing paradigm have demonstrated that chimpanzees also are capable of responding to addition and subtraction manipulations on these arrays, and also that chimpanzees can retain numerical information resulting from enumeration processes for extended time periods (up to 20 minutes). We have examined the link between these types of numerousness judgments and the formal counting skills acquired by children. We have postulated that counting skill is not required for children to be sensitive to arithmetic manipulations as such a sensitivity appears to be widespread phylogenetically.  This research is supported by the National Institute of Child Health and Human Development (HD-38051).

Selected Related Publications:

Beran, M. J., French, K., Smith, T. R., & Parrish, A. E. (2019). Limited evidence of number-space mapping in rhesus monkeys (Macaca mulatta) and capuchin monkeys (Sapajus apella). Journal of Comparative Psychology, 133, 281-293. 

Beran, M. J., & Parrish, A. E. (2016). Capuchin monkeys (Cebus apella) treat small and large numbers of items similarly during a relative quantity judgment task. Psychonomic Bulletin & Review, 23, 1206-1213.

Beran, M. J., McIntyre, J. M., Garland, A., & Evans, T. A. (2013).  What counts for “counting”? Chimpanzees (Pan troglodytes) respond appropriately to relevant and irrelevant information in a quantity judgment task.  Animal Behaviour, 85, 987-993. 

Beran, M. J., & Parrish, A. E. (2013). Visual nesting of stimuli affects rhesus monkeys’ (Macaca mulatta) quantity judgments in a bisection task. Attention, Perception, & Psychophysics, 75, 1243-1251.