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

Abstract

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.

Congenital facial palsy and emotion processing: The case of Moebius syndrome

“…The controversial role of facial mimicry in emotional processing can be better evaluated by studying what happens when the muscles of the face are experimentally blocked or impaired. If facial mimicry plays a causal role in understanding other people's emotions, blocking or reducing facial movements should make emotion recognition more difficult, for example, by reducing the accuracy of the detection of facial expressions …”

“…The motor system is therefore fundamental to operate such simulation and to translate the perception of an emotion into the corresponding motor representation. In support to this model, we reviewed several EMG experiments showing that any interference with the simulation process, such as blocking facial muscles, could affect others' emotions recognition . Given such theoretical perspective, in the current review we addressed the following questions: what happens when individuals have motor deficits in the use of facial muscles, which prevent them from mimicking the facial expressions of others?…”

“…If facial mimicry plays a causal role in understanding other people's emotions, blocking or reducing facial movements should make emotion recognition more difficult, for example, by reducing the accuracy of the detection of facial expressions. 149,150 Clinical evidence found a lower face recognition performance in Parkinson's disease patients than in matched healthy controls. 151,152 However, it should be noted that neurological diseases presenting facial amimia (such as Parkinsonism or Huntington disease) could present other symptoms such as impaired movement initiation, rigidity, tremors, postural instability and, in particular, reduced expressivity not only in the face but also in the body and voice.…”

“…In support to this model, we reviewed several EMG experiments showing that any interference with the simulation process, such as blocking facial muscles, could affect others' emotions recognition. 149,150 Given such theoretical perspective, in the current review we addressed the following questions: what happens when individuals have motor deficits in the use of facial muscles, which prevent them from mimicking the facial expressions of others? Do these deficits impact the process of the recognition of others' emotions?…”

Spontaneous Facial Actions Map onto Emotional Experiences in a Non-social Context: Toward a Component-Based Approach

“…Thus, the regression models requiring hierarchical structures that can include random effects of both participants and stimuli could not converge in this study. Also, we could not explore the asymmetry of facial expressions, which is relevant to the domain of spontaneous facial actions (Mammucari et al, 1988; Ross and Pulusu, 2013; Korb et al, 2016; see review by Murray et al, 2015), because the occurrence rate of applicable action units was too low in our data to evaluate the specificity of sidedness. Moreover, we cannot contribute anything to the debate on cultural differences or the universality of facial components related to emotional experiences.…”