, Volume 29, Issue 2, pp 107-119

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

Abstract

Herrnstein and Loveland (1964, pp. 549–551) successfully trained pigeons to discriminate pictures showing humans from pictures that did not. In the present study, a go/no-go procedure was employed to replicate and extend their findings, the primary focus of concern being to reevaluate the role of item- and category-specific information. The pigeons readily acquired the discrimination 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 global features (Experiment 2). The presentation of gray-scale stimuli indicated that color was important for classifying novel stimuli and recognizing familiar 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 pictures (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 precedence over the former.

The research was supported by Grant P-10975-BIO from the Austrian Science Foundation. We thank Michaela Loidolt, who prepared Experiments 1 and 2 and also helped to carry them out. Thanks are also due Dieter Grass, who developed the MATLAB computer program for gradual scrambling. Finally, we thank Renate Nowotny and Michael Pollirer for their assistance in the pigeon laboratory.