Pre-conscious reactions to faces as the biological roots of emotion perception

Bodies respond to others’ emotions through subtle physiological changes. Whether these responses require conscious emotion recognition is debated. Here, we examined the relationship between visual awareness and physiological arousal in response to emotional faces. We recorded facial electromyography (EMG), electrodermal activity (EDA), and pupil dilation during the presentation of fearful, happy, and neutral faces, as well as their phase-scrambled versions, to the left eye. Meanwhile, rapidly changing Mondrian patterns were displayed to the right eye to suppress the left-eye stimuli. Participants pressed a button when they noticed a change from the flickering mask. This setup allowed us to compare behavioural and physiological responses during conscious versus subconscious processing of emotional content. Results showed faster breakthrough times for happy faces and moderate physiological responses to emotional information, even without conscious perception. Specifically, pupils and facial EMG were more responsive to fearful than to happy or neutral expressions. EDA was higher for faces compared to control stimuli, regardless of the emotional expression. Once visual awareness was established, emotional expressions elicited distinct responses that aligned with the perceived emotion. An exploratory analysis revealed a negative correlation between pupil dilation and autistic, alexithymic, and schizotypal traits, whereas empathy traits correlated positively. Our findings highlight the role of subcortical visual processing in detecting emotionally relevant stimuli and show that social abilities are linked to the physiological processing of emotions at a subconscious level. They underscore how subcortical mechanisms interact with the autonomic nervous system, enhancing our understanding of the biological foundations of emotion perception.