Numerical matching behavior by a chimpanzee (Pan troglodytes): Subitizing and analogue magnitude estimation

A female chimpanzee (Pan troglodytes) received numerical matching-to-sample training. The comparative stimuli used in ail experiments were Arabic numerals. The sample stimuli in Experiment 1 were semi-random patterns of one to six dots displayed on a computer monitor. in addition to the increase of dot numbers to seven, three specific patterns were mixed into random patterns in Experiment 2. The sizes of dots were changed between and within sessions during Experiment 3. A set of objects in different colors and forms was displayed on the video monitor as a sample in Experiment 4. Results of these experiments showed that the chimpanzee was able to label, with numerals up to seven, a set of dots as well as objects displayed in a homogeneous or heterogeneous pattern. Reaction time as a function of the number of dots suggested that her performance was based on subitizing and estimation of magnitude analogous to the number.