Objectives: To explore phase-locked gamma and beta responses to the Kanizsa square in TD children and to look for their possible abnormalities in ASD children.
Methods: We used illusory Kanizsa square and control non-illusory stimuli (experimental procedure described in Stroganova et al., 2007) to test how the phase-locked gamma and beta EEG responses of 23 typically developing (TD) children aged 3 to 7 years and those with ASD were modulated by the presence of IC in the image.
Results: The phase-locked beta and gamma activity strongly differentiated between IC and control figures in both groups of children (IC effect). However, the timing, topography, and direction of the IC effect differed in TD and ASD children. Between 40 and 120 ms after stimulus onset, both groups demonstrated lower power of gamma oscillations at occipital areas in response to IC than in response to the control figure. In TD children, this relative gamma suppression was followed by relatively higher parieto-occipital gamma and beta responses to IC within 120 to 270 ms after stimulus onset. This second stage of IC processing was absent in children with ASD. Instead, their response to IC was characterized by protracted (40-270 ms) relative reduction of gamma and beta oscillations at occipital areas.
Conclusions: These data suggest different modes of ICs processing in TD and ASD children. We hypothesize that children with ASD rely more heavily on lower-order processing in the primary visual areas and have atypical later stage related to higher-order processes of contour integration.
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See more of: Brain Structure & Function