Cortical sensitivity to contrast polarity and orientation of faces is modulated by temporal-nasal hemifield asymmetry.

Abstract

Behavioral studies demonstrate that the efficiency of detection of faces is dependent on configural and contrast polarity information characteristic to human faces. Stimulus inversion or contrast polarity reversal can disrupt this process. We investigated whether a face-sensitive event-related potential component, the N170, is modulated by the orientation and contrast polarity of highly degraded schematic face-like patterns (Experiment 1) in the same manner as it is for face photographs (Experiment 2). Inversion and/or contrast reversal delayed and enhanced the N170 for both kinds of stimuli, suggesting that a white oval with three black squares is sufficient to elicit face-sensitive cortical responses. In Experiment 3 we further tested whether the extrageniculate visual pathways modulate early cortical responses to faces. We found that the N170 responses to configural and contrast information are modulated by temporal-nasal visual field asymmetry under monocular viewing conditions, suggesting the involvement of subcortical, extrageniculate visual pathways in face detection. These results are consistent with the idea that an ontogenetically early and primitive bias to orient towards face-like patterns with relevant configural and contrast information influences the early stages of cortical face processing.