Human brain detection of natural brief facial expression at a single glance

Abstract published in Neurophysiologie Clinique, 49(3):199, June 2019National audienceBackground: The processing of emotional facial expressions has been studied mainly with stereotypical and posed face stimuli. In the human brain, brief facial expression changes are quickly read from faces (Dzhelyova et al., 2017).Objectives: The purpose of this study is to know how reliably brief changes are detected with realistic faces embedded in a natural context.Methods: In this study, faces varied in viewpoint, identity, gender, age, ethnic origin and background context. We recorded 128-channel EEG in 17 participants while they viewed 50s sequences with neutral-expression faces at a rate of 5.99 Hz (F) at two faces orientations (upright, inverted). Every five faces, the faces changed expression to one of the six basic expression (fear, disgust, happiness, anger, surprised or sadness; Ekman, 1993), one emotion per sequence. EEG responses at 5.99 Hz reflect general visual processing, while the EEG responses at F/5 = 1.1998 Hz and its harmonics (e.g., 2F/5 = 2.3996, etc.) index detection of a brief change of natural facial expression.Results: At group level, the categorization response was measured over occipito-temporal sites and was largely reduced when faces were inverted, indicating that it reflects high-level processes. Our observations with natural expressions highlight a stronger response for a shift from neutral to sad faces, especially over the left hemisphere. Moreover, we observed a right hemisphere dominance for fearful faces and a left hemisphere dominance for surprised faces.Conclusion: Human brain is able to detect automatically in natural scenes dynamic brief facial expression changes