Environmental inversion effects in face perception.

Visual processing is highly sensitive to stimulus orientation; for example, face perception is drastically worse when faces are oriented inverted vs. upright. However, stimulus orientation must be established in relation to a particular reference frame, and in most studies, several reference frames are conflated. Which reference frame(s) matter in the perception of faces? Here we describe a simple, novel method for dissociating effects of egocentric and environmental orientation on face processing. Participants performed one of two face-processing tasks (expression classification and recognition memory) as they lay horizontally, which served to disassociate the egocentric and environmental frames. We found large effects of egocentric orientation on performance and smaller but reliable effects of environmental orientation. In a follow-up control experiment, we ruled out the possibility that the latter could be explained by compensatory ocular counterroll. We argue that environmental orientation influences face processing, which is revealed when egocentric orientation is fixed.