Contextual Modulation: Components of the Rod-and-Frame Illusion and the Systemizing Trait of Autism
Adams, David John
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Adams, David John
Individuals with autism tend to have superior sensory discrimination abilities and a locally-oriented cognitive style. The mechanisms that underlie these phenomena are unknown and may be linked to atypicalities in the contextual modulation occurring through mutually inhibitory interactions of neurons in early visual cortex. Prior wo·rk, in both monkeys and humans, has demonstrated that the perceived orientation of a line is distorted when presented in the context of other tilted lines (flankers), with the magnitude and direction of these effects dependent on the orientation and location of the flankers. With collateral flankers, the test line is perceived to be tilted away from flankers with 15 degree tilts, but this "perceptual repulsion" becomes smaller (or even a "perceptual attraction") with smaller flanker tilts. Experiment I examined the relationship between these contextual effects and the systemizing trait of autism. Individuals who scored high on the "insistence on sameness" subcomponent of systemizing were more sensitive in their orientation judgments, while showing a greater repulsive effect of the flankers. However, when the flankers were replaced with a small ii iii tilted frame, the resulting repulsive effects (known as the Rod-and-Frame illusion) were even larger, but they were uncorrelated with insistence on sameness. In Experiment 2, we dissected the frame into its component parts in an attempt to determine the specific features that drive the orientation contrast effects of the Rodand- Frame illusion. We discovered that the left and right sides of the frame induced a significantly smaller repulsive effect than lateral flankers of the same tilt. However, the top and bottom of the frame induced a large repulsive effect that even exceeded that of the intact frame. These results indicate that the Rod-and-Frame illusion is the result of an underadditive combination of two independent contextual effects, though neither of these effects are correlated with insistence on sameness. Future work should further investigate this underadditivity, as well as the link between autism and local contrast effects. Such work may provide clues into how neural architecture differs in individuals with autism.