The Contribution of Visual Attention to Performance on Tests of Nonverbal Ability in Adolescents with Intellectual Disability with and without Comorbid Autism Spectrum Disorder

Background:  Few studies have considered how visual attention contributes to solving the visual items on nonverbal IQ tests especially for individuals with Intellectual Disability (ID) with and without Autism Spectrum Disorder (ASD) where fast activation and maintenance of visual attention is characteristically problematic.

Objectives:  To identify the contribution of rapid activation of visual attention to the nonverbal IQ tests scores of adolescents with ID and typically developing (TD) children of comparable mental age.

Methods:  We compared the performance of both groups on the Raven’s Coloured Progressive Matrices, the Test of Nonverbal Intelligence –Fourth Edition and the Wechsler Nonverbal Scale of Ability, nonverbal IQ (NVIQ) test and threshold performance on 4 visual tasks requiring rapid and maintained activation of attention i.e., motion coherence, inspection time (IT), contrast threshold for illusory figures, and change detection. Multiple regression analyses were utilized to compare the contribution of the 4 visual attention tests scores to variance on NVIQ scores. Furthermore, as it is well accepted that many adolescents with ID also show co-morbid symptoms of Autism Spectrum Disorder (ID+ASD), we compared the performance on all tasks of the individuals with ID non-ASD and those with ID+ASD.

Results:  Performance of the ID group was worse than that of the TD group on all visual attention tasks especially the IT task, which contributed significant variance to nonverbal tests scores for the ID group but not for the TD group. Threshold visual attention scores also contributed substantial amounts of variance to NVIQ test scores for the ID+ASD but not for the ID non-ASD group.

Conclusions: Our results suggest that adolescents with ID are slower to activate visual attention and complete visual NVIQ test items than children with TD of a similar mental age. The finding that the ID+ASD performed less well than the ID non-ASD confirms earlier observations that attention deficits are greatest for those with more severe ID and co-morbid ASD.