Visual classes and natural categories in the pigeon.

After being trained on an oak leaf pattern, pigeons responded to other oak leaf patterns but not to leaf patterns of other species, suggesting graphic variation among the instances of a species is "transparent" to the visual system.

Abstract

After being trained on an oak leaf pattern, pigeons responded to other oak leaf patterns but not to leaf patterns of other species. Thus, graphic variation among the instances of a species is "transparent" to the visual system. At this taxonomic level, concept formation is spontaneous rather than inductive. It is argued that such immediate generalization may be critical to the survival of the organism.