CATEGORICAL DISCRIMINATION AND GENERALIZATION IN PIGEONS - ALL NEGATIVE STIMULI ARE NOT CREATED EQUAL

Three experiments investigated categorical discrimination and generalization in pigeons. Multiple fixed interval-extinction training was conducted with a pool of 48 different negative discriminative stimuli (12 slides each of people, flowers, cars, and chairs). The most errors were committed to negative stimuli (S-s) from the same category as the 12 positive stimulus (S+) slides. Such categorical generation was stronger when the 12 S+s entailed 1 copy of 12 different slides (Experiment 2) than when the S+s entailed 12 copies of 1 slide (Experiment 1). In addition, reliable but incomplete loss of inhibitory control was observed to novel stimuli chosen from the same category as the S- slides (Experiment 3). These results are consistent with perceptual theories of categorical coherence, according to which preexisting similarities among stimuli chiefly determine the acquisition and application of categories.