Spatial Processing and Contour Integration In Children with Autism 6-16 Years of Age

Background: It has been observed with increasing frequency that, in addition to the behavioral manifestations of autism spectrum disorders (ASD) which present to the naked eye, there are atypicalities at more basic levels of processing.  For instance, there is some suggestion that low level visual processing is atypical in individuals with autism (Vandenbroucke et al., 2008).   The typical adult brain can interpolate object identity under less than optimal viewing conditions, permitting gaps to be bridged in the contours of incomplete or obstructed objects, a process called perceptual completion.  Kanizsa-type illusory contours (IC) are a stimulus class frequently employed to study this phenomenon.  When pacman-shaped disks are oriented so that the contours of their “mouths” are precisely aligned and not too far from one another, the viewer can close the gap between them, perceiving continuous contours even though none exist.  Event-related potential studies (e.g. Murray et al., 2002, Foxe et al., 2005) have extensively investigated this phenomenon, establishing a set of robust dependent measures underlying the binding of components into objects within the ventral visual stream.  An early, automatic, contour-dependent ERP component occurring at approximately 110-200 ms, termed the IC effect, appears to be the earliest sensitivity to IC stimuli measurable with ERP. It has been localized to a cluster of ventral stream regions known as the lateral occipital complex, associated with object processing.

Objectives: We sought to better understand the limits of the automatic, contour-dependent phase of perceptual completion by taxing IC processing in typical and ASD children.  We hypothesized that differences in basic visual processing and/or the tendency of persons with ASDs to default to processing parts over wholes, might weaken the strength of the illusion or increase the processing requirements of binding, differences that would be made manifest in the amplitude or the latency of the well-characterized IC effect.

Methods: ERPs to IC stimuli were compared between typical and ASD children, in two age cohorts: 6-10 and 11-16, as well as in a normal healthy adult cohort. IC- inducing stimuli were presented at three retinal eccentricities (4, 7 and 10 degrees).  IC-effect amplitudes and latencies were measured for each.

Results: Results from typical adults replicate Murray et al’s (2002) IC effect, and demonstrate indifference of either effect amplitude or peak latency to the manipulation of eccentricity. This pattern appears to be replicated in typically developing children and ASD children ages 11-16, however, preliminary analyses indicate a less robust IC-effect for the ASD younger cohort as a result of the parametric manipulation.  

Conclusions: These data indicate that automatic completion of object contours is accomplished by older children with ASD in a comparable fashion to their typical counterparts.  Our preliminary analyses of the data suggest that there might be a deficit in contour completion in the younger ASD group.  However, additional analyses are required before strong conclusions can be drawn.