Two-item conditional same-different categorization in pigeons: Finding differences.

Research on same-different categorization has shown that mastery of tasks of this kind can be strongly affected by the number of items in the training arrays-for both humans and nonhuman animals. Evidence for two-item same-different categorization in pigeons is decidedly mixed: although some investigations have succeeded, others have failed. To date, no research has documented successful conditional same-different categorization using just two items, nor has research explored how pigeons' responses in this paradigm might be influenced by perceptual characteristics of the training stimuli. Through a series of methodological modifications, we provide the first successful documentation that pigeons can perform two-item conditional same-different categorization to a high degree of accuracy; further, they can do so without the support of item repetition. We also show for the first time that the perceptual disparity between the items in pairs of different stimuli plays a key part in pigeons' same-different categorization performance. (PsycInfo Database Record (c) 2021 APA, all rights reserved).