Phase-Linked EEG Alpha Activity on Perception of an Illusory Kanisza Square in Healthy and Autistic Boys of Preschool Age

Abstract

The time dynamics of the power of phase-linked EEG alpha oscillations were studied on presentation of an illusory (Kanizsa square) and control non-illusory image to children aged 4–7 years with normal development and with childhood autism. Analysis of variance showed that in the group of children with normal development, the “illusion effect,” consisting of an increase in the power of alpha-oscillations in response to the illusory figure, had, on average, a right-sided lateralization. Analysis of the continuity of the illusion effect using a simplex method showed that this group contained children showing this effect bilaterally. In the group of children with autism, analysis of variance did not show an illusion effect, though the simplex method showed that this group included children demonstrating an anomalously early “illusion effect,” located above the occipital cortex, and/or a late effect present on the EEG of the left parietal area. These results suggest that the asymmetry of the “illusion effect” in the group of normally developing children shows incompleteness of the processes forming the “intermediate” mechanisms of perception of the whole object. The atypical “illusion effect” in autism may result from hyperfunction of “low-level” mechanisms of processing outlines in combination with dysfunction of the “intermediate” mechanisms of perceptual grouping.