Numerical Matching Behavior by a Chimpanzee (Pan troglodytes): Subitizing and Analogue Magnitude Estimation

Abstract

A female chimpanzee (Pan troglodytes) received numerical matching‐to‐sample training. The comparative stimuli used in all 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.

Enumeration of briefly presented items by the chimpanzee (Pan troglodytes) and humans (Homo sapiens)

“…When she was 5 years old, she was initially trained on a numerical labeling task by using Arabic numerals (1 to 6) and real-life objects (Matsuzawa, 1985;Matsuzawa et al, 1986). The objects were later replaced by white dots appearing on a CRT display that also included the numbers 7, 8, 9, and 10 (Matsuzawa et al, 1991;Murofushi, 1997). Concurrently with the present experiment, she was also trained on sequential responding with Arabic numerals (Tomonaga, Itakura, & Matsuzawa, 1993;Tomonaga & Matsuzawa, 2000; see also Biro & Matsuzawa, 1999;Kawai & Matsuzawa, 2000).…”

“…Miller (1993) suggests that modifying the original meaning of these processes to explain the various types of results from animal experiments is not acceptable. To use response times as data, it is necessary to teach "numerals" to animals, a simple, human-like, but difficult task (Biro & Matsuzawa, 2001a, 2001bBoysen & Berntson, 1989;Ferster & Hammer, 1966;Matsuzawa, 1985;Matsuzawa, Asano, Kubota, & Murofushi, 1986;Matsuzawa, Itakura, & Tomonaga, 1991;Murofushi, 1997;Pepperberg, 1987Pepperberg, , 1994.…”

“…This training in numerical labeling was later continued by replacing the real objects with white dots presented on a computer monitor Murofushi, 1997). The chimpanzee was successively introduced to larger numbers up to 10.…”

“…She showed improved accuracy and faster response times on the largest number, relative to the second largest number at each training period. Murofushi (1997) argued that the chimpanzee might use analogue magnitude codes during the numerical labeling task but might not use the codes as humans use them. An apparent increase in response times from 5 to the second largest number provides time for a different process from counting.…”

Cognitive access to numbers: the philosophical significance of empirical findings about basic number abilities

“…The author of the study took the RT data to suggest that for numbers up to 3 Ai was probably subitizing and for numbers beyond 3 estimating rather using non-verbal counting; and the estimation probably involved a comparison of representations from an analogue magnitude system. 23 Ai was later trained to name the number in computer displays of 1 to 9 items. At 20 years she was trained with the aim of incorporating "0" into her stock of numerals as a symbol for absence of items 24 .…”