Binocular depth modulates high-level visual perception without awareness

Abstract

Binocular depth does not always break through top-down suppression to consciousness when the stimuli have intrinsic depth property. For example, the back of a hollow mask is consistently interpreted as a normal face by healthy people (Dima et al., 2009; Schneider et al., 1996); and depth-scrambled point-light walkers are perceptually regulated into normal walkers through stereoscopic vision (Bülthoff et al., 1998). Do these seemly uncompetitive and subliminal binocular depth cues have any functional role in high-level visual perception? Using 3D point-light walkers presented with stereoscopic glasses, we identified a subgroup of participants (20%) who incorrectly interpreted all the rear-view (facing away from the viewer) 3D walkers as facing toward themselves. Despite that they couldn't discern between the 3D walkers with opposite facing directions in a forced-choice task, they had no difficulty in identifying moving direction of non-biological 3D objects. Most crucially, these participants were more sensitive in discriminating the walking direction of the walkers (left vs. right) that were facing toward than away from them, similar to the response pattern observed from the participants who accurately perceived the 3D walkers in depth. Our results demonstrate that binocular depth information could be sometimes registered independent of depth perception and modulate high-level visual perception.