Dissociating the perception of speed and the perception of animacy: a functional approach

Differences in acceleration, differences in constant speed and illusory speed differences are all associated with predictable differences in animacy perception. The current study describes a dissociation between perceived speed and perceived animacy, apparently resulting from the human visual system taking gravity into account. In Experiment 1, participants compared dots moving at the same speed up and down a vertically oriented computer screen. Dots moving up were judged as animate more often than dots moving down, while dots moving down were judged as faster most often. To test whether this pattern of results was sensitive to changes in the orientation of the stimuli relative to gravity, Experiment 2 presented the same stimuli on a screen oriented horizontally. The dissociation between the perception of speed and the perception of animacy was maintained: The difference between the perception of animacy of dots moving away vs. toward was much reduced, while the effect on speed perception was more pronounced, compared to the vertical orientation. These results are consistent with the idea that the human visual system is designed to perceive animacy in a functionally reasonable way given the terrestrial environment in which it evolved.