Conceptual Behavior in Pigeons: Categorization of Both Familiar and Novel Examples From Four Classes of Natural and Artificial Stimuli

Abstract

Two new procedures-a four-key choice procedure and a four-ply multiple fixed ratio schedule procedure-were used to train pigeons to categorize color slides depicting natural (cat, person, flower) and human-made (car, chair) objects. In Experiments 1 A, 1 B, 2 A, and 2 B, 16 pigeons trained with 10 slides from each of four categories reliably classified novel examples from these categories. However, performance was more accurate on training than on novel stimuli. In Experiment 3, 8 pigeons learned to classify 2,000 nonrepeating slides. Thus, repetitive training with a limited number of stimuli is not necessary for pigeons to learn a four-category classification task. In Experiment 4, 4 pigeons were trained with a set of repeating slides while concurrently being trained with novel stimuli. As in Experiments 1 A, 1 B, 2 A, and 2 B, performance here was more discriminative on repeatedly seen stimuli than on novel ones. Thus, repetition facilitates categorization, whether or not the pigeons are concurrently exposed to novel stimuli. The implications of these results for models of categorization are discussed. We conclude that the conceptual abilities of pigeons are more advanced than hitherto suspected.