Behavioural sensitivities to disparity-defined faces

Abstract

We tested the perception of disparity-defined depth under naturalistic and unnaturalistic contexts. Stimuli consisted of random-dot stereograms depicting upright faces, inverted faces, or curvature-matched surfaces. Observers completed two tasks in which they were asked to judge whether the target was in front or behind of a surround (SNR task) or which of two consecutively presented targets was nearer (feature task). Stimulus difficulty was manipulated by adjusting the percentage of dots laying on versus off the target's surface (SNR task), or adjusting the disparity difference between the two consecutively presented targets (feature task), via a staircase (QUEST) procedure. For the feature-discrimination task, thresholds were lower (better) for the curvature-matched control surface, than for the face stimuli at either orientation. Thresholds for the SNR task, however, did not differ across the three conditions. Our data suggest that object context can significantly influence disparity judgments, potentially as a consequence of feedback from traditional extrastriate object-related regions.