Luminance- and Texture-Defined Spatial Information Processing In School-Aged Children with Autism

Background:  Low-level visual perception in adult individuals with Autism Spectrum Disorders (ASD) is different from that of neurotypical individuals. For example, sensitivity to luminance-defined spatial information has been demonstrated to be superior in ASD, whereas sensitivity to texture-defined information is less efficiently perceived (Bertone et al., 2005; Vandenbroucke et al., 2009). These results have been interpreted as resulting from atypical connectivity both (i) within the primary visual cortex (V1), where luminance information is extracted, and (ii) between primary and adjacent extra-striate visual areas (V2, V3) where recurrent neural interactions mediate texture-defined information (Baker & Mareschal, 2001). However, it is currently unknown if the neural alterations underlying such elementary visual processes are present in children with ASD.

Objectives:  To assess luminance- and texture-defined spatial information processing in children with autism using behavioural (psychophysical) and electrophysiological (visual evoked-potentials: VEPs) approaches.

Methods:  Seventeen autistic and 25 typically developing children, aged 6 to 10 years, with normal or corrected-to-normal vision, were matched on age, gender and intelligence. The visual stimuli were luminance- and texture-defined gratings, presented either vertically or horizontally within a circular aperture for 750 ms.

Psychophysical task:  Participants were asked to discriminate the orientation of luminance- and texture-defined gratings presented at five contrast levels (luminance modulations: 0.25%, 0.5%, 1%, 2%, 5%; texture modulations: 5%, 10%, 15%, 20%, 50%). Each pattern was shown 10 times in a pseudo-randomized order. Orientation-identification thresholds were obtained using a method of constant stimuli, and defined as the contrast level needed to attain a 75% correct level of performance.

Electrophysiological task: Participants were presented with luminance- and texture-defined gratings with contrast levels of 6% and 100%, respectively, in order to equate their visibility. Gratings from each condition were presented 160 times (80 vertical and 80 horizontal presentations). Participants were asked to fixate the center of the display while their brain activity was recorded using a high-density electrophysiological system. At posterior sites on the scalp, the early VEP component associated with pattern processing (P1) was examined for latency, amplitude and scalp distribution.

Results:  Psychophysical results suggest comparable mean contrast sensitivity between autistic and control children for both luminance- (p = .70) and texture-defined conditions (p = .42). Additionally, no group differences were found for electrophysiological measures. Nonetheless, we observed that the P1 component was modulated by the type of information presented in the expected direction. Specifically, P1 amplitude was greater at occipital midline (Oz) for luminance-defined gratings (p < .05), while occipitotemporal sites (PO7; PO8; P7; P8) tended to be more responsive to texture-defined information (p = .09).

Conclusions:  School-aged children with autism appear to process luminance- and texture-defined spatial information similarly to typically developing children, therefore contrasting with adolescent/ adult findings. Given the important developmental changes that occur during the school age years, we are presently analyzing and comparing behavioural and electrophysiological data as a function of age within each group. Findings will be discussed within the context of the Enhanced Perceptual Functioning (Mottron et al., 2006) and the Complexity-Specific (Bertone & Faubert, 2006) perceptual hypotheses in ASD.