Social motivation modulates early visual processing for a few others' emotions

Emotional faces, compared to neutral ones, have been shown to elicit enhanced early event-related potentials (ERPs) even in the absence of expression-related goals. The phenomena reflect implicit facilitation in early visual processing, in which viewers' interpersonal traits may play a role. Although there is a vast literature for single faces, social interactions often involve encounters with multiple others. The present study aimed to reveal whether facial expressions of more than one other implicitly modulate early visual processing, by examining the effects of the numerosity of task-irrelevant happy faces and individual differences in empathic concern on early ERPs. Participants viewed arrays of three face photographs, in which the number of happy faces ranged from zero to three (with the remaining faces displaying neutral expressions), while pressing a button to infrequent non-face targets. Results showed that the happy-face numerosity and the self-reported empathic-concern tendency jointly modulated posterior P1 and N170 amplitudes, the pattern of which indicates that prioritized expressions may vary depending on the level of trait empathic concern and processing stages. The finding suggests an interplay between the processing of multiple individuals' facial expressions and a viewer's other-oriented social motivation, which implies a dynamic nature of early visuo-attentional processes for a small number of others' emotional states.