ARE FACES OF DIFFERENT SPECIES PERCEIVED CATEGORICALLY BY HUMAN OBSERVERS

What are the species boundaries efface processing? Using a face-featur e morphing algorithm, image series intermediate between human, monkey (macaque), and bovine faces were constructed. Forced-choice judgement of these images showed sharply bounded categories for upright face ima ges of each species. These predicted the perceptual discrimination bou ndaries for upright monkey-cow and cow-human images, but not human-mon key images. Species categories were also well-judged for inverted face images, but these did not give sharpened discrimination (categorical perception) at the category boundaries. While categorical species judg ements are made reliably, only the distinction between primate faces a nd cow faces appears to be categorically perceived, and only in uprigh t faces. One inference is that humans may judge monkey faces in terms of human characteristics, albeit distinctive ones.