The role of item- and category-specific information in the discrimination of people versus nonpeople images by pigeons

Herrnstein and Loveland (1964, pp. 549-551) successfully trained pigeons to discriminate pictures showing humans from pictures that did not. In the pr esent study, a go/no-go procedure was employed to replicate and extend thei r findings, the primary focus of concern being to reevaluate the role of it em- and category-specific information. The pigeons readily acquired the dis crimination and were also able to generalize to novel instances of the two classes (Experiment 1). Classification of scrambled versions of the stimuli was based on small and local features, rather than on configural and globa l features (Experiment 2). The presentation of gray-scale stimuli indicated that color was important for classifying novel stimuli and recognizing fam iliar ones (Experiments 1 and 2). Finally, the control that could possibly be exerted by irrelevant background features was investigated by presenting the pigeons with images of persons contained in former person-absent pictu res (Experiment 3). Classification was found to be controlled by both item- and category- specific features, but only in pigeons that were reinforced on person-present pictures was the latter type of information given precede nce over the former.