Are children with autistic spectrum disorders susceptible to contour illusions?

Children with autism have been shown to be less susceptible to Kanisza type contour illusions than children without autism (Happé, 1996). Other authors have suggested that this finding could be explained by the fact that participants with autism were required to make a potentially ambiguous verbal response which may have masked whether or not they actually perceived the illusory contours (Ropar & Mitchell, 1999). The present study tested perception of illusory contours in children with autism using a paradigm that requires participants to make a forced choice about the dimensions of a shape defined by illusory contours. It was reasoned that accuracy of the participant on this task would indicate whether or not children with autism could perceive illusory contours. A total of 18 children with autistic spectrum disorder, 16 children with special educational needs not including autism and 20 typically developing children completed an experimental task which assessed perception of Kanisza-style rectangles defined by illusory contours. There were no significant differences between the performance of the children with autism and either of the two control groups, suggesting that perception of illusory contours is intact in autism.