Rats counting rats: The use of conspecifics as discriminative stimuli

Abstract

Although a variety of experimental procedures have shown considerable evidence of “counting” in animals, there is no evidence of numerical competence when conspecifics are used as test stimuli. Here, we report evidence of a relative numerousness (2 vs. 4) judgment by rats that were required to discriminate the number of free-ranging conspecifics in an arena. This discrimination was ultimately disrupted by vigorous social interaction between the subjects and the to-be-counted rats. Attempts to restrict the movement of object rats in Experiment 2 did not lead to reestablishment of the discrimination, although 2 animals did show evidence of a simple presence versus absence (0 vs. 5) discrimination, a precursor of numerical ability. © 1992, Psychonomic Society, Inc.. All rights reserved.