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Abstract:
Five chimpanzees were tested on their ability to discriminate
faces and automobiles presented in both their upright and inverted
orientations. The face stimuli consisted of 30 black and white
photographs, ten each of upright and inverted chimpanzees (Pan
troglodytes), brown capuchins (Cebus apella), and humans (Homo
sapiens). Ten black and white photographs of automobiles were also
used. The stimuli were presented in a sequential,
matching-to-sample format using a computerized, joystick-testing
apparatus. Subjects performed better on upright than inverted
stimuli in all classes. Performance was significantly better on
upright versus inverted presentations of chimpanzee and human
faces, not capuchin monkey faces or automobiles. These data support
previous studies in humans that the inversion effect occurs for
stimuli for which subjects have developed an expertise. Alternative
explanations for the inversion effect based on the type of spatial
frequency contained in the stimuli, and mode of visual processing,
are also discussed. These data are the first to provide evidence
for the inversion effect using several classes of face stimuli in a
great ape species.
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