Abstract
The purpose of this study is to examine the influence on the perception of animacy of visual motion cues or information. The study focuses on the preference in predatory activity of squirrel monkeys on the basis of whether their baits or feeds are alive or dead. In experiment 1a, two mealworms (one alive and the other dead) were simultaneously placed in front of the monkeys to investigate whether they could discriminate between the alive and dead mealworms based on whether they are moving or not. We introduced a mechanical rotary movement to see if the monkeys could distinguish a natural movement of living matter from the artificial rotary movement. The monkeys showed a preference for the live mealworms over the dead ones, suggesting that the mechanical motion did not influence the predatory activity of the monkeys. In experiment 1b, taking into consideration the possibility of the monkeys discriminating between the alive and dead mealworms, using other cues than the motion information used in experiment 1a, we introduced differences in constant brightness, shape, and placement among the stimuli. Thus, the monkeys were completely forced to choose the mealworms, using only the motion cues. The results we obtained are similar to those obtained in experiment 1a, indicating that the monkeys perceived animacy from the motion cues. In experiment 2, we presented moving images of similar stimuli to human subjects under the same conditions as those used for experiments 1a and 1b, and asked human subjects to select that one of the images which gave a stronger impression in terms of biological features. The result of this experiment suggested that motion information mediates animacy perception in common to squirrel monkeys and humans.