Neural measures of the causal role of observers' facial mimicry on visual working memory for facial expressions

Abstract

Simulation models of facial expressions propose that sensorimotor regions may increase the clarity of facial expressions representations in extrastriate areas. We monitored the event-related potential marker of visual working memory (VWM) representations, namely the sustained posterior contralateral negativity (SPCN), also termed contralateral delay activity, while participants performed a change detection task including to-be-memorized faces with different intensities of anger. In one condition participants could freely use their facial mimicry during the encoding/VWM maintenance of the faces while in a different condition participants had their facial mimicry blocked by a gel. Notably, SPCN amplitude was reduced for faces in the blocked mimicry condition when compared to the free mimicry condition. This modulation interacted with the empathy levels of participants such that only participants with medium-high empathy scores showed such reduction of the SPCN amplitude when their mimicry was blocked. The SPCN amplitude was larger for full expressions when compared to neutral and subtle expressions, while subtle expressions elicited lower SPCN amplitudes than neutral faces. These findings provide evidence of a functional link between mimicry and VWM for faces and further shed light on how this memory system may receive feedbacks from sensorimotor regions during the processing of facial expressions.

Fig. 1

(A) Examples of the stimuli used in the change detection task, one for each three level of facial expression (neutral, intermediate, full) for two individual faces (one of a female and one of a male). (B) The pictures show how the gel mask limited the facial movements of a participant for two different facial expressions (of anger at the top and happiness at the bottom).

Fig. 2

Timeline of each trial of the change detection task.

Fig. 3

Mean proportion of correct responses in the change detection task for each facial expression condition (neutral, subtle and full).

Fig. 4

Grand averages of the face-locked ERP waveforms time-locked to the presentation of the memory array as a function of the facial expression conditions (neutral, subtle and full) collapsed across the mimicry conditions (free vs altered/blocked).

Fig. 5

Grand averages of the face-locked ERP waveforms time-locked to the presentation of the memory array as a function of the mimicry conditions (free vs altered/blocked) and collapsed across facial expression conditions (neutral, subtle and full) for medium-low EQ participants (A) and medium-high EQ participants (B) separately.