The discrimination of mirror-image forms by pigeons

Abstract

Four experiments investigated the discriminability of mirror-image forms with pigeons. Experiments 1-3 used U-shaped forms, oriented up, down, right, and left. The first experiment found non-mirror images better discriminated than mirror images on a matching-to-sample task. Experiment 2 found up-down reversals better discriminated than left-right mirror images on a three-key simultaneous discrimination task. Experiment 3 replicated this result with a single stimulus presentation method on a go/no-go discrimination. The final experiment repeated Experiment 2 with F-shaped forms whose mirror images could not be produced by a 180-deg rotation, but only by a reflection about the horizontal or vertical axis. These results are consistent with most findings for human and nonhuman subjects, but contrary to a recent suggestion by Hollard and Delius (1982) that mirror-image forms are distinct for pigeons. © 1983 Psychonomic Society, Inc.