Perceiving Animacy From Deformation and Translation

In a cartoon, we often receive an animacy impression from a dynamic nonanimate object, such as a sponge or a flour sack, which does not have an animal-like shape. We hypothesize that the animacy impression of a nonanimal object could stem from dynamic patterns that are possibly fundamental for biological motion perception. Here we show that observers recognize the animacy of human jump actions from the combination of deformation and translation. We extracted vertical motion vectors from the uppermost and lowermost points in point-light jumper stimuli and assigned the vectors to a uniform rectangle. The participants' task was to rate the animacy and jump impressions for the rectangle. Results showed that both animacy and jump impressions for the rectangle movements were comparable to those for the original point-light movements. The impressions decreased for stimuli having a deformation or translation component alone, which was extracted from the original motion vectors. By mathematically simulating deformation and translation in a human jump, we also found that the temporal relation between deformation and translation plays a critical role in the determination of jump impressions but only has a moderate effect for animacy impressions. On the basis of the results, we discuss how cartoon techniques take advantage of the properties of biological motion perception.