Memorization and “feature selection” in the acquisition of natural concepts in pigeons☆

Abstract Pigeons were trained on a successive discrimination task using complex visual stimuli. In Experiment 1, each photographic slide that contained a person had a corresponding “matched background” slide, one that showed the same scene with the person removed. Birds trained on a human positive discrimination acquired the matched pairs problem, but birds trained on a human negative discrimination performed poorly. This suggests a feature-positive effect for complex stimulus categories. Memorization control groups that were trained on a human-irrelevant discrimination also performed poorly with matched slides. However, subsequent experiments demonstrated that these effects depended on the use of matched pairs of slides. The human-as-feature effect was not obtained when human positive and human negative groups were subsequently trained with non-matched slides (Experiment 2), and memorization control groups acquired a human-irrelevant discrimination when trained with nonmatched slides (Experiment 3). Additional tests conducted in Experiments 2 and 3 found that performance was not disrupted when either the reinforced or nonreinforced slides were replaced. This effect was obtained when the category was relevant to the discrimination (Experiment 2) and when the category was irrelevant to the discrimination (Experiment 3). Finally, Experiment 4 demonstrated that memorization of a set of slides is possible when slides are sufficiently dissimilar, (i.e., nonmatched) but performance is not as good when the category exemplars are irrelevant to the discrimination.