Investigating the Face Inversion Effect in Autism Across Behavioral and Neural Measures of Face Processing: A Systematic Review and Bayesian Meta-Analysis.

This research looked at how people with autism process faces differently. When faces are shown upside-down, most people find them much harder to recognize - this is called the 'face inversion effect.' The study found that autistic people showed less of this effect, meaning their face recognition wasn't as disrupted by inverted faces. This suggests that autistic people may process faces differently, with less specialized brain systems for face recognition, especially for reading emotions from faces.

This systematic review and meta-analysis examined face processing differences in autism by analyzing the face inversion effect across 38 studies with 1,764 participants (899 autistic, 865 neurotypical). The face inversion effect measures how recognition accuracy decreases when faces are shown upside-down, indicating specialized face processing. Results showed autistic individuals had a significantly reduced face inversion effect (g = -0.41), suggesting less specialized face processing systems. This difference was more pronounced for emotion recognition compared to identity recognition, and in behavioral versus electrophysiological measures.

The findings indicate that autistic individuals may have less expertise or specialization in face processing, particularly for emotional facial expressions.

These findings suggest that face processing interventions for autistic individuals may need to focus particularly on emotion recognition skills. The reduced specialization in face processing systems indicates that traditional face training approaches may need modification. Assessment of social communication difficulties should consider these fundamental differences in face processing mechanisms.

The study showed considerable heterogeneity among effect sizes, indicating variability across studies. Moderator analyses had wide credible intervals, suggesting uncertainty in some findings. The review was limited to studies measuring face inversion effects specifically, which may not capture all aspects of face processing differences in autism.

Face processing is foundational to human social cognition, is central to the hallmark features of autism spectrum disorder (ASD), and shapes neural systems and social behavior. Highly efficient and specialized, the face processing system is sensitive to inversion, demonstrated by reduced accuracy in recognition and altered neural response to inverted faces. Understanding at which mechanistic level the autistic face processing system may be particularly different, as measured by the face inversion effect, will improve overall understanding of brain functioning in autism. To synthesize data from the extant literature to determine differences of the face processing system in ASD, as measured by the face inversion effect, across multiple mechanistic levels.

Systematic searches were conducted in the MEDLINE, Embase, Web of Science, and PubMed databases from inception to August 11, 2022. Original research that reported performance-based measures of face recognition to upright and inverted faces in ASD and neurotypical samples were included for quantitative synthesis. All studies were screened by at least 2 reviewers. This systematic review and meta-analysis was conducted according to the 2020 Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline.

Multiple effect sizes were extracted from studies to maximize information gain and statistical precision and used a random-effects, multilevel modeling framework to account for statistical dependencies within study samples. Effect sizes were calculated as a standardized mean change score between ASD and neurotypical samples (ie, Hedges g). The primary outcome measure was performance difference between upright and inverted faces during face recognition tasks. Measurement modality, psychological construct, recognition demand, sample age, sample sex distribution, and study quality assessment scores were assessed as moderators.

Of 1768 screened articles, 122 effect sizes from 38 empirical articles representing data from 1764 individual participants (899 ASD individuals and 865 neurotypical individuals) were included in the meta-analysis. Overall, face recognition performance differences between upright and inverted faces were reduced in autistic individuals compared with neurotypical individuals (g = -0.41; SE = 0.11; 95% credible interval [CrI], -0.63 to -0.18). However, there was considerable heterogeneity among effect sizes, which were explored with moderator analysis. The attenuated face inversion effect in autistic individuals was more prominent in emotion compared with identity recognition (b = 0.46; SE = 0.26; 95% CrI, -0.08 to 0.95) and in behavioral compared with electrophysiological measures (b = 0.23; SE = 0.24; 95% CrI, -0.25 to 0.70).

This study found that on average, face recognition in autism is less impacted by inversion. These findings suggest less specialization or expertise of the face processing system in autism, particularly in recognizing emotion from faces as measured in behavioral paradigms.