This meta-analysis summarized studies that examined group differences on the production of facial expressions in participants with ASD compared to typically developing or nonautistic clinical comparison groups. The overall summary effect from 67 effect sizes representing the average ASD-comparison group differences in facial expressions was -0.481, indicating a moderate effect size. We conducted subgroup analyses to group effect sizes according to separate facial expression abilities identified in the literature. These analyses revealed that participants with ASD display facial expressions less frequently and for less amount of time, and they are less likely to share facial expressions with others or automatically mimic the expressions of real faces or face stimuli. Their facial expressions are also judged to be lower in quality and are expressed less accurately. However, participants with ASD do not express emotions less intensely, nor is their reaction time of expression onset slower in response to odors, startling sensations, or in response to face stimuli in mimicry studies. ASD-comparison group differences were moderated by matching procedures, age, and intellectual functioning of the ASD participants suggesting that persons with higher IQ and larger number of accumulated life experiences are better able to produce facial expressions that are more consistent with "neurotypical" norms. Group differences were also stronger for "covertly elicited" than "explicitly elicited" facial expressions suggesting individuals with ASD may naturally produce facial expressions differently from other populations, but are less impaired in expressing emotions typically when prompted to do so in a laboratory setting. Autism Research 2018, 11: 1586-1601. © 2018 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: We reviewed studies that compared facial expressions in people with and without autism. Results revealed that facial expressions of people with autism are atypical in appearance and quality and are used atypically to regulate social interactions. The magnitude of these differences was influenced by participant characteristics (e.g. age and intellectual functioning), and by how facial expressions were measured and analyzed in various studies.
Keywords: autism; facial expressions; meta-analysis.
© 2018 International Society for Autism Research, Wiley Periodicals, Inc.