Intracranial EEG recordings from face-selective temporal cortex show enhanced response to contralateral face information

Despite behavioral and neuropsychological evidence for a right hemisphere bias for face processing, and a corresponding left hemifield advantage for faces, neurally much remains unknown about the division of labor in face processing between the right and left fusiform. In particular, there remain gaps in our understanding of the role of bilateral face-selective areas in contributing to dynamic representation of face information. To clarify the effects of visual hemifield on bilateral fusiform dynamics, we recorded intracranial encephalography (iEEG) data from 4 patients with electrodes placed directly on right and/or left face-selective temporal cortex. While fixating, participants completed a gender discrimination task in response to 16 face-halves presented individually to the right or left of fixation (4 unique male and female faces divided into 8 left and right halves, yielding 16 unique images). Taking the grand average from the broadband signal, we found that electrodes placed in both right and left temporal cortex show an enhanced response to face-halves presented in the contralateral visual hemifield. This difference between contra- and ipsilateral face-halves emerges within the first 50 ms after stimulus presentation, with both hemispheres showing an early peak at ~160 ms. Signal differences persist throughout the 500 ms following stimulus presentation, with a second peak occurring at ~350 ms in right-lateralized electrodes and ~480 ms in left-lateralized electrodes. We examine identity decoding to determine whether identity processing has a hemifield bias and to assess whether a face-half invariant identity code is seen in the fusiform and when it emerges. Together, these results highlight both early and persistent differences in the hemispheric representational dynamics of face processing based on visual hemifield of stimulus presentation. Meeting abstract presented at VSS 2018