Asymmetry of Facial Mimicry and Emotion Perception in Patients With Unilateral Facial Paralysis

Abstract

Importance: The ability of patients with unilateral facial paralysis to recognize and appropriately judge facial expressions remains underexplored.

Objective: To test the effects of unilateral facial paralysis on the recognition of and judgments about facial expressions of emotion and to evaluate the asymmetry of facial mimicry.

Design, setting, and participants: Patients with left or right unilateral facial paralysis at a university facial plastic surgery unit completed 2 computer tasks involving video facial expression recognition. Side of facial paralysis was used as a between-participant factor. Facial function and symmetry were verified electronically with the eFACE facial function scale.

Exposures: Across 2 tasks, short videos were shown on which facial expressions of happiness and anger unfolded earlier on one side of the face or morphed into each other. Patients indicated the moment or side of change between facial expressions and judged their authenticity.

Main outcomes and measures: Type, time, and accuracy of responses on a keyboard were analyzed.

Results: A total of 57 participants (36 women and 21 men) aged 20 to 76 years (mean age, 50.2 years) and with mild left or right unilateral facial paralysis were included in the study. Patients with right facial paralysis were faster (by about 150 milliseconds) and more accurate (mean number of errors, 1.9 vs 2.5) to detect expression onsets on the left side of the stimulus face, suggesting anatomical asymmetry of facial mimicry. Patients with left paralysis, however, showed more anomalous responses, which partly differed by emotion.

Conclusions and relevance: The findings favor the hypothesis of an anatomical asymmetry of facial mimicry and suggest that patients with a left hemiparalysis could be more at risk of developing a cluster of disabilities and psychological conditions including emotion-recognition impairments.

Level of evidence: 3.