Perception of human chimeric faces by chimpanzees: evidence for a right hemisphere advantage

The aim of this study was to investigate hemispheric advantages in the processing of human chimeric faces by chimpanzees using a free-vision task developed by Levy, Heller, Banich, and Burton (1983a). Subjects were taught a visual discrimination in which they were to select the human face that appeared "happiest" when paired with its neutral counterpart. After reaching criterion, chimeric faces were substituted as test trials, and the face the subjects selected was recorded. On 62% of the trials, three chimpanzee subjects selected the face in which the smiling half fell in the left hemispatial field. Familiarity factors appear to have accounted for some of the observed findings. We believe this is the first evidence for hemispheric advantages in the perception of human faces by great apes.