Autism Spectrum Disorder (ASD) is a pervasive developmental disorder described by behavioral symptoms, evident before the age of three, that can be divided into three groups: abnormalities in social interaction and play (e.g. problems in making eye contact), atypical communicative skills (e.g. absence or limited use of gestures and facial expressions and delayed language development), and stereotyped and repetitive patterns of behavior (e.g. queuing up toy cars over and over again). Besides these higher-level cognitive impairments, there is a growing body of evidence that ASD also encompasses pure perceptual aberrancies such as enhanced visual detail perception and probably also altered global processing and visual grouping. Although ASD is a genetically determined, neurodevelopmental disorder, there is as yet no generally accepted neural explanation for atypical visual perception in these patients. In this PhD thesis we tried to establish the neural basis of atypical visual perception in ASD by studying integration properties of the visual system, necessary for global processing, as well as the integrity of neural interactions associated with detail perception and grouping. Using electro-encephalography (EEG) and functional MRI we have provided evidence for an aberrancy in low-level visual processing in ASD, which we related to atypical lateral inhibition through horizontal interactions in early visual areas. Interestingly, this impairment could be compensated later in time through enhanced processing in the angular gyrus, possibly reflecting increased local attention. We conjecture that the combination of disrupted early processing with compensation at higher levels may be a general feature of the physiology of perception in ASD. Although the relation between these findings and enhanced detail perception is merely implicit, malfunctioning of horizontal interactions can explain aberrant perceptual grouping in people with ASD. Interestingly, from neurochemistry and neuropathology research aberrant lateral inhibition in other brain areas besides the occipital cortex has been inferred. Altogether, we speculate that aberrant horizontal interactions reflect a more general neural abnormality in this disorder. Studying these neural interactions more thoroughly in the future could be a promising direction for research on visual perception in particular and possibly for ASD in general
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