Frames of reference for biological motion and face perception.

We investigated the roles of egocentric, gravitational, and visual environmental reference frames for face and biological motion perception. We tested observers on face and biological motion tasks while orienting the visual environment and the observer independently with respect to gravity using the York Tumbling Room. The relative contribution of each reference frame was assessed by arranging pairs of frames to be either aligned or opposed to each other while rendering the third uninformative by orienting it sideways relative to the stimulus. The perception of both biological motion and faces were optimal when the stimulus was aligned with egocentric coordinates. However, when the egocentric reference frame was rendered uninformative, the perception of biological motion, but not faces, relied more on stimulus alignment with gravity rather than the visual environment.