The body inversion effect in chimpanzees (Pan troglodytes)

抄録

Bodies are important social cues for animals. Humans show decreased performances in body recognition when bodies are inverted, compared to when they are upright. This inversion effect suggests the configural processing of bodies, which is different from the way used to process other objects. However, it is not known whether it exists in non-human primates. We tested seven chimpanzees using upright and inverted chimpanzee body stimuli and other stimuli in matching-to-sample tasks to examine the body inversion effect in order to understand their body processing. Experiment 1 used stimuli of chimpanzee bodies and houses. Experiment 2 used stimuli of intact bodies, bodies with blurred faces, and faces with blurred bodies. Experiment 3 used stimuli of intact bodies, bodies without faces, only faces, and body silhouettes. The chimpanzees showed the inversion effect to all intact body conditions, indicating the configural body processing. They also showed the inversion effect to faces with blurred bodies in Experiment 2 and to silhouettes in Experiment 3, suggesting the roles of faces and body contours in the inversion effect. The results suggest that chimpanzees use special cognitive processing to process bodies, which is different from the way they use for other objects, and that faces and body contours are important cues for body configural processing.