Abstract
Facial expression recognition is shaped by both stimulus properties and the perceiver’s affective state. Research on emotional face processing under backward masking has largely focused on threatening expressions, and few studies have examined how an observer's mood influences recognition of non-threatening facial expressions under limited visibility. The present study investigated how experimentally induced sad versus neutral mood modulates behavioral and neural responses to sad and neutral facial expressions under low (10 ms) and high visibility (200 ms) backward masking conditions. Participants underwent sad and neutral mood induction on separate days and performed a facial expression categorization task while electroencephalography was recorded. Behavioral and event-related potential (ERP) analyses included 25 and 20 participants, respectively. Behaviorally, a mood effect on response criterion was observed in the low visibility condition: the criterion was lower in sad than neutral mood, reflecting a reduced tendency to categorize faces as neutral. Discrimination sensitivity was higher under high than low visibility but was not significantly affected by mood. Facial expressions modulated N170, P2, and P3 amplitudes under high visibility, and N170 and P2 under low visibility. P2 amplitude in the low visibility condition showed an interaction effect between mood and facial expression. In neutral mood, sad faces elicited larger P2 amplitudes than neutral faces, whereas in sad mood, the relation was the opposite. These findings highlight the influence of the observer’s affective state on behavioral and neural responses to facial expressions under limited visibility, extending previous findings beyond threat-related expressions to sadness.