Social Functioning in Autistic Children with Below-Average vs. Average IQ: Limited Behavioral and Neural Evidence of Group Differences.

Despite the relatively high rates of intellectual disability (ID) in autism, research studies and clinical trials commonly exclude autistic participants with below-average IQ. This study aimed to characterize the effect of intellectual ability on social functioning in autistic adolescents assessed using behavioral and neural measures. Caregiver reports and direct standardized behavioral assessments of social abilities along with event-related potential measures of social and nonsocial information processing were obtained in school-age children with autism and ID (n = 41) matched on age, sex, and autism symptom severity to autistic participants with average IQ (n = 41). Full-scale IQ differences did not affect caregiver reports of social functioning in daily life. Group differences were observed only for the direct behavioral assessments of social perception and cognition (NEPSY Memory for Faces delayed, Theory of Mind) as well as social behavior with an unfamiliar friendly confederate, where higher IQ was associated with better performance. Similarly, the impact of IQ on neural responses was limited to a minimal delay in the processing speed of all visual stimuli and the magnitude of differences between social and nonsocial images, but not on incidental memory for the repeated stimuli. The effects of IQ on behavioral or neural responses did not vary based on biological sex. Below-average full-scale IQ in autistic youth affects results of some but not all behavioral or neural measures probing social functioning. Therefore, enrolling participants with a wider range of intellectual ability could be feasible in future studies.