Early processing of unattended emotional faces increases the brain response to attended emotional expressions: an SSVEP study

Abstract

The brain has the ability to evaluate unattended social information, such as facial expressions, and reassign attentional resources to specific relevant features. Two neuronal mechanisms could account for such facial emotional processing: one slow and accurate system that can be measured around 170 ms and one fast and imprecise system that is triggered around 90 ms which could support early negative emotional processing for automatic/unattended and peripheral stimulation. Evidence that these mechanisms exist for positive affective processing is scarce. The present study investigated the neural correlates of unattended negative and positive emotional processing using the rapid presentation of unilateral and bilateral peripheral facial expressions. Hence, we measured the electrophysiological correlates of unattended fear, happy and neutral faces presented in the left and right hemifields of neurotypical individuals using a frequency tagging paradigm and electroencephalography. Frequency stimulations of 5.8 Hz and 11 Hz were chosen to induce Steady-State Visual Evoked Potential (SSVEP) occurring at 170 ms and 90 ms, respectively. The SSVEP amplitudes showed that unattended positive and negative information in the periphery was processed at early stages and increased the brain's response to attended salient emotional stimuli in posterior visual regions. These results suggest that emotional stimuli presented outside the attentional focus elicit increased brain activity, particularly in posterior regions which could be altered in disorders of social recognition.