Sensitivity to motion features in point light displays of biological motion.

Psychophysical experiments are described that measure the sensitivity to motion features in point light displays of biological motion. Three motion features were investigated: the relative motion of the thighs, the relative motion of the thigh and leg, and the velocity profile of the leg. The perceptual threshold for discriminating a change in each motion feature was compared in upright and inverted point light displays. We find that subjects are more sensitive to two of the motion features in the upright display configuration (relative motion of thighs, relative motion of thigh and leg), but more sensitive to the third feature (velocity profile of the leg) in the inverted configuration. We propose that perceptual sensitivity to features used in biological motion perception should be greater in upright versus inverted displays. The results suggest that motion features differ in salience in biological motion perception.