Abstract
Pigeons and humans chose which one of two alternative visual forms was identical to, or a mirror image of, a previously presented sample form. The two comparison forms were presented in various orientations with respect to the sample. The two species yielded similar accuracies, but although human reaction times depended linearly on the angular disparities, those of the pigeon did not. Humans appeared to apply a well-known, thoughtlike, mental rotation procedure to the problem, whereas pigeons seemed to rely on a more efficient automatic process that humans can use only in simpler rotational invariance tasks. Mirror-image forms may be better discriminated by the pigeon's visual system than by the human one.
