Within-hemifield perceptual averaging of facial expressions predicted by neural averaging

Abstract

High-level visual neurons in the ventral stream typically have large receptive fields, supporting position-invariant object recognition but entailing poor spatial resolution. Consequently, when multiple objects fall within their large receptive fields, unless selective attention is deployed, their responses are averages of responses to the individual objects. We investigated a behavioral consequence of this neural averaging in the perception of facial expressions. Two faces (7 degrees -apart) were briefly presented (100-ms, backward-masked) either within the same visual hemifield (within-hemifield condition) or in different hemifields (between-hemifield condition). Face pairs included happy, angry, and valence-neutral faces, and observers rated the emotional valence of a post-cued face. Perceptual averaging of facial expressions was predicted only for the within-hemifield condition because the receptive fields of 'face-tuned' neurons are primarily confined within the contralateral field; the between-hemifield condition served to control for post-perceptual effects. Consistent with averaging, valence-neutral faces appeared more positive when paired with a happy face than when paired with an angry face, and affective intensities of happy and angry faces were reduced by accompanying valence-neutral or opposite-valence faces, in the within-hemifield relative to the between-hemifield condition. We thus demonstrated within-hemifield perceptual averaging of a complex feature as predicted by neural averaging in the ventral visual stream.