Facial expression adaptation impairs perceived social signal across expressions.

Facial expressions provide crucial cues for assessing others' internal states, leading to appropriate responses to maintain social harmony. This study investigated how social signals evoked by facial expressions are perceived, focusing on their automatic triggering and relationship to the representations of the expressions by using adaptation aftereffect paradigm. Participants evaluated their perceived need for help and their motivation to provide help in response to sad and fearful expressions, both of which convey help signals, before and after adaptation. Accordingly, the ratings for perceived need for help for both sad and fearful expressions decreased following adaptation to sad expressions, indicating that perceived need for help was represented independently from the perception of test expressions. Additionally, this result also indicates that the need for help is automatically triggered during viewing sad facial expressions. However, the ratings for perceived need for help for fearful expressions alone decreased after adaptation to fearful expressions. The motivation to help remained unaffected by adaptation to sad or fearful expressions. Additional experiments demonstrated that impairment of perceived need for help occurs independently of the perceived intensity of the expressions and participants' moods. This study suggests that social signals can be represented independently from facial expressions, and facial expression adaptation paradigms can examine this possibility.