Objectives: The aim of this study is to investigate, using visual evoked potentials (VEPs), the neuronal correlates of local luminance and texture perception in school-aged autistic children.
Methods: Autistic and typically developing children, aged 6 to 10 years, were matched on handedness, gender, chronological age and intelligence based on Raven’s Standard Progressive Matrices. All children had normal or corrected-to-normal vision. In a texture segregation task based on orientation, children were presented with four high contrast visual stimuli on a display while their brain activity was being recorded using a high-density electrophysiological system. Stimuli were shown 120 times each in a block sequence. Children were not required to respond to stimuli. To only record trials where the child was attending, one experimenter present in the testing room signaled the child’s behaviour (via button press) to the adjacent control room. Testing sessions were also video recorded for later verification. Two stimuli were low-level orientation patterns (ORI) defined by homogeneous oblique lines oriented either to the right or left. Two stimuli were segregated texture patterns (TEX) composed of the same oblique lines but presented in an orientation-defined checkerboard (90º line gradients), oriented either concentrically or outwards. A texture segregation VEP (tsVEP) was isolated by subtracting the ORI- from the TEX-VEP response. The tsVEP reflects neuronal integration between V1 and V2/V3, mainly via feedback from V2/V3 to V1. Early VEP components (P1, N2) at occipital sites were examined for latency, amplitude and scalp distribution across all conditions.
Results: Preliminary results indicate that compared to controls, the P1 component in the autism group shows delayed but larger and sustained activity at occipital sites (Oz, O1, O2) for both ORI and TEX conditions. In the control group, the tsVEP appears as a negative deflection at around 194ms post-stimulation, as expected from the literature. In contrast, autistic children demonstrate reduced amplitude of this negative deflection.
Conclusions: Autistic children appear to process low-level orientation and segregated texture patterns differently from typically-developing children, and both low-level and texture processing contribute at altering texture segregation mechanisms. These findings will be discussed within the framework of the enhanced perceptual functioning model (Mottron et al., 2006) and the complexity-specific hypothesis for perceptual information processing in autism (Bertone & Faubert, 2006).