Patterns of Nonsocial and Social Cognitive Functioning in Adults with Autism Spectrum Disorder: A Systematic Review and Meta-Analysis

Background: Despite similar Autism Spectrum Disorders (ASD) prevalence rates of 1% in children and adults, and clear challenges that persist into adulthood, research and treatment efforts have been largely dedicated to children. A critical question that has remained largely unaddressed concerns the identification of cognitive domains that are most severely impaired in adults with an ASD diagnosis. A detailed evaluation and comparison of (social) cognitive deficits in adults with ASD will advance knowledge about the expression of ASD in later life, and may help pinpoint targets for (social) cognitive intervention.

Objectives: The present review and meta-analysis aims to systematically map the severity of impairments across domains of non-social and social cognitive functioning in adults with ASD compared to the neurotypical adult population. To help explain any variability between studies, potential moderators of impairments observed in these individuals will be evaluated.

Methods: The literature search was conducted in PubMed, PsycINFO, EMBASE and MEDLINE databases. The search was limited to studies published between 1980 (first inclusion of Autism diagnosis in the DSM-III) and July 2018. Studies were included if they were published as primary peer-reviewed research paper in English, included individuals with Autism Spectrum Disorder (ASD) aged 16 or over and assessed at least one domain of neurocognitive functioning or social cognition using standard measure(s). In total, 9829 potentially eligible papers were identified and screened, 75 studies met inclusion criteria for meta-analysis.

Results: Most of the 75 studies included in the meta-analysis were conducted in Europe (n=50, 67%), followed by studies from the USA and Canada (n=16, 21%). The sample sizes varied greatly, ranging from 18 to 3907 participants (including neurotypical adults) with 66 (88%) studies using samples between 20 and 100 participants. All the included studies had a combined sample of 3361 individuals with ASD and 5344 neurotypical adults. Adults with ASD showed large impairments in theory of mind (Effect size (ES) g=-1.09, 95% CI=-1.25 to -0.92; number of studies=39) and emotion perception and knowledge (ES=-0.80, 95% CI=-1.04 to -0.55; n=18), followed by medium impairments in processing speed (ES=-0.61, 95% CI=-0.83 to -0.38; n=21) and verbal learning and memory (ES=-0.55, 95% CI=-0.86 to -0.25; n=12). The relatively spared cognitive domains were working memory (ES=-0.23, 95% CI=-0.47 to 0.09; n=19) and attention and vigilance (ES=-0.30, 95% CI=-0.81 to 0.21; n=5). Meta-regressions confirmed robustness of the results.

Conclusions: This comprehensive review and meta-analysis of impairments in non-social cognitive functioning and social cognition of verbal adults with ASD showed that despite having an intact IQ, there are medium to large deficits observed in four key-domains of social and non-social cognition (Theory of Mind, Emotion perception and knowledge, Processing speed and Verbal learning and memory). While our findings support the key social cognitive theories of ASD, they also stress deficits in non-social cognitive areas. These results highlight the importance of a broader approach when studying cognition, also as potential mechanism underlying symptoms and treatment outcomes.