Spatial Frequency Processing in 3- and 4-year-olds with Autism Spectrum Disorder (ASD)

Background: Besides difficulties in social interaction, people with ASD have an atypical visual processing style which is more detail oriented than in typical subjects (Happe and Frith, 2006). This might be explained by abnormal spatial frequency (SF) processing in ASD (Boeschoten et al., 2007). Any input to the visual system consists of luminance variations at various frequencies across space. Low spatial frequencies (LSF) capture large-scale variations (coarse information) whereas high spatial frequencies (HSF) represent small-scale variations (detailed information).

Objectives: In the present study we investigate whether abnormal SF processing is already present in ASD in early childhood and how this is reflected in the brain. We predict faster and/or elevated processing of HSF in ASD.

Methods: Nineteen ASD children (3/4 years) and 21 age matched controls were presented with 90 HSF and 90 LSF gratings, during which EEG was recorded. Diagnosis of ASD was defined as meeting criteria for ASD at the Autism Diagnostic Observation Schedule (ADOS) and Autism Diagnostic Interview Revised (ADI-R).

Results: Children with ASD showed higher P1 amplitudes for HSF than for LSF, whereas this was not significant in controls. No latency differences between ASD and controls were found for the P1 (positivity at 100 ms) and N2 (negativity at 200 ms) at OZ (electrode above the visual cortex).

Conclusions: In typical adults, amplitude differences between HSF and LSF gratings at the P1 are linked to the involvement of different brain areas for HSF and LSF (Ossenblok & Spekreijse, 1990). The present data suggest that the visual system might be more differentiated and mature at an early age in ASD, as the pattern of larger P1 amplitudes to HSF than LSF gratings is also seen in typical adults.