The efficiency of biological motion perception

Humans can readily perceive biological motion from point-light (PL) animations, which create an image of a moving human figure by tracing the trajectories of a small number of light points affixed to a moving human body. We have applied ideal observer analysis to a standard biological motion discrimination task involving either full-figure or PL displays. Contrary to current dogma, we find that PL animations can be rich in potential stimulus information but that human observers are remarkably inefficient at exploiting this information. Although our findings do not discount the utility of PL animation, they do provide a realistic measure of the computational challenge posed by biological motion perception.