International Meeting for Autism Research (London, May 15-17, 2008): Illusory Contour Effect in Healthy and Autistic Children

Friday, May 16, 2008

Champagne Terrace/Bordeaux (Novotel London West)

A. Prokofyev , Moscow State University of Psychology and Education, Moscow, Russia

E. Orekhova , Institute of Neuroscience and Physiology, Sahlgrenska Academy, Gothenburg University, and Massachusetts General Hospital, Boston, Gothenburg, Sweden

I. Posikera , Psychological Institute of the Russian Academy of Education, Moscow, Russia

A. Morozov , Institute of Radio Engineering and Electronics of the Russian Academy of Sciences, Moscow, Russia

V. Morozov , Institute of Radio Engineering and Electronics of the Russian Academy of Sciences, Moscow, Russia

Y. Obukhov , Institute of Radio Engineering and Electronics of the Russian Academy of Sciences, Moscow, Russia

T. Stroganova , Psychological Institute of the Russian Academy of Education, Moscow, Russia

Background: Autism syndrome is characterized by atypical visuoperceptual processing that is usually interpreted in terms of the reduction in the contextual integration of information. It is assumed that this reduction is related with dysfunction of neural mechanisms of ‘intermediate’ vision which can be studied using the illusory contour paradigm.

Objectives: The study examined the hypothesis of lower-level processing abnormalities related to perceptual grouping in boys with autism aged 3 to 6 years. We investigated event-related potentials response to visual elements that either formed perceptually coherent illusory contour or were arranged in a noncoherent way.

Methods: The subjects were 19 boys with autism aged 3-6 years and 19 age-matched typically developing boys. Electroencephalogram (EEG) was recorded from the 19 electrodes (10-20 International System) and digitized at 500 Hz. EEG was registered while the subject passively viewed two types of visual stimuli which were presented pseudorandomly. Non-parametric analysis of the amplitude and latency values of the N1 component was performed for six posterior scalp regions of interest: O1, O2, P3, P4, OZ, PZ.

Results: In typically developing boys, the illusory contour as compared with control stimulus elicited enhanced negativity of N1 peak (illusory contour effect), which has been previously found in adults. The illusory contour effect on N1 amplitude in typically developing boys was most pronounced at parietal areas of the right hemisphere. Boys with autism demonstrated the reliable inverted illusory contour effect, that is, more positive N1 amplitude to illusory contour at occipital areas. The latency of N1 peak in response to illusory contour did not differ between two groups of children.

Conclusions: We hypothesized that sensitivity to difference between illusory contour and control figures in boys with autism is based on collinearity processing mechanisms implemented in neural circuitry of primary visual cortex.

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