Developmental Changes in the Cognitive Profile of Individuals with Autism Spectrum Disorders

Background:  Individuals with autism spectrum disorders (ASD) often present with variable cognitive profiles.  Despite showing deficits in their verbal abilities, many children with ASD have intact or superior nonverbal skills (Joseph, Tager-Flusberg, & Lord, 2002) and a relative strength in their visuospatial reasoning (Green, Fein, Joy, & Waterhouse, 1995). However, some research has shown that Full Scale IQ (FSIQ), Verbal IQ (VIQ), and Performance IQ (PIQ) scores improve with age in children with ASD, with the gap between VIQ and PIQ eventually closing (Mayes & Calhoun, 2003).  While such profiles have been relatively well documented in children with ASD, research examining cognitive profiles of ASD across the lifespan is rather limited.

Objectives:  The main objective of this study was to examine the cognitive profile (i.e., VIQ, PIQ, and FSIQ) of high-functioning children and adults with ASD, and compare it to typically developing (TD) control participants.

Methods:  Participants were high-functioning individuals (i.e., FSIQ > 70) with and without ASD.  The current sample consists of 75 children (ages 8 to 18 years; 47 ASD and 28 TD) and 70 adults (ages 19 to 40 years; 31 ASD and 39 TD). All participants completed the Wechsler Abbreviated Scales of Intelligence (WASI) to obtain a measure VIQ, PIQ, and FSIQ.  Correlational analyses and two-way between-groups ANOVAs were conducted to explore the impact of age (i.e., child or adult) and diagnosis (i.e., ASD or TD) on FSIQ, VIQ, and PIQ.  An independent samples t-test was conducted to compare the PIQ-VIQ difference between children and adults with ASD.  

Results:  FSIQ, VIQ and PIQ scores were significantly positively correlated with age in both the ASD and TD groups (r = .49, .47, and .34 respectively; p < .001).  The FSIQ, VIQ, and PIQ of adults were significantly higher than that in children, for both individuals with ASD and TD (F(1,142) = 47.66, 43.71, and 18.17 respectively; p < .001).  The main effect of diagnosis was only significant for VIQ (F(1,142) = 5.81, p < .01), with a greater increase in VIQ scores from the child to adult group for ASD participants (17.16 points) as compared to TD participants (13.38 points). Although PIQ was higher than VIQ in both child and adult ASD participants, these differences were not statistically significant (t(76) = .76, p= .45).

Conclusions:  The results of this study revealed that IQ scores increased with age for both ASD and TD participants.  However, individuals with ASD showed greater increases in VIQ from childhood to adulthood, perhaps because the verbal skills of children with ASD may have been more likely to be targeted during school interventions than their nonverbal skills. Notably, there were no significant differences between the VIQ and PIQ scores of children or adults with ASD.  This suggests that the PIQ-VIQ difference may not be apparent in high-functioning individuals with ASD, or as Mayes and Calhoun (2003) found, this gap may close prior to age 8 (the youngest age in our sample). Further analyses of the data are in progress.