Facial expression recognition as a candidate marker for autism spectrum disorder: how frequent and severe are deficits?

Background: Impairments in social communication are a core feature of Autism Spectrum Disorder (ASD). Because the ability to infer other people's emotions from their facial expressions is critical for many aspects of social communication, deficits in expression recognition are a plausible candidate marker for ASD. However, previous studies on facial expression recognition produced mixed results, which may be due to differences in the sensitivity of the many tests used and/or the heterogeneity among individuals with ASD. To ascertain whether expression recognition may serve as a diagnostic marker (which distinguishes people with ASD from a comparison group) or a stratification marker (which helps to divide ASD into more homogeneous subgroups), a crucial first step is to move beyond identification of mean group differences and to better understand the frequency and severity of impairments. Methods: This study tested 46 individuals with ASD and 52 age-and IQ-matched typically developing (TD) participants on the Films Expression Task, which combines three key features of real-life expression recognition: naturalistic facial expressions, a broad range of simple and complex emotions, and short presentation time. Testretest reliability was assessed in 28 individuals who did not participate in the main study and revealed acceptable reliability (ICC r =.74). Results: Case-control comparisons showed highly significant mean group differences for accuracy (p = 1.1 x 10(-10)), with an effect size (Cohen's d = 1.6), more than twice as large as the mean effect size reported in a previous metaanalysis (Uljarevic and Hamilton, 2012, J Autism Dev Disord). The ASD group also had significantly increased mean reaction times overall (p =.00015, d =.83) and on correct trials (p =.0002, d =.78). However, whereas 63% of people with ASD showed severe deficits (they performed below two standard deviations of the TD mean, a small subgroup (15.3%) performed normally (within one standard deviation of the mean). Conclusion: These findings indicate that the majority of people with ASD have severe expression recognition deficits and that the Films Expression Test is a sensitive task for biomarker research in ASD. Future work is needed to establish whether ASD subgroups with and without expression recognition deficits differ from one another in terms of their symptom profile or neurobiological underpinnings.