Abstract
The biomechanical limitations of the human body constrain the visual perception of apparent body motion (Shiffrar & Freyd, 1990). Numerous findings suggested that face processing is distinct from body processing. This raises the question of whether the structure of the human face influences the visual perception of apparent face motion. To answer this question, participants viewed two-frame apparent motion sequences that depicted photographs and drawings of human faces in which the two eyes blinked in alternation. Frame duration varied from 100 to 700 ms in 100 ms steps and the interstimulus interval was fixed at 0 ms. The stimuli were constructed so that two percepts were possible: (1) a physically possible motion in which the two eyes remained in their fixed locations and blinked in alternation, or (2) a physically impossible motion in which the visible eye appeared to translate back and forth between the two eye sockets. On each trial, subjects reported whether they perceived the possible or impossible apparent motion. Following a between subjects design, participants in Experiment 1, viewed chromatic and achromatic faces that were upright or inverted. Observers reported the perception of possible blinking motion with upright faces and the perception of impossible eye translation with inverted faces. Thus, holistic face processing changed apparent motion perception. In Experiment 2, the two alternately blinking eyes were presented in isolation, either upright or inverted. In this case, orientation had no effect on apparent motion perception. Thus, apparent motion differs for faces and isolated eyes. Taken together, these results suggest that the visual analysis of the face influences the visual perception of apparent motion. If so, then neural activity in area FFA might constrain activity in area MT.