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Natalie Dill, Richard Krauzlis; Reaction times and perceptual judgments are atypical in autism. Journal of Vision 2008;8(6):368. doi: https://doi.org/10.1167/8.6.368.
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Subjects with autism have greater difficulty than controls discriminating the direction of visual motion, suggesting the presence of abnormalities at early stages of visual processing. Alternatively, this difficulty could be attributed to differences in how perceptual judgments are formed. To test this possibility, we measured reaction times as well as choices in a motion discrimination task.
Subjects (ASD-diagnosed adolescents and typically developing controls) performed a 2AFC visual motion discrimination task. After subjects fixated a central spot, a stochastic motion patch (8° diameter, centered 8° above fixation) was presented along with two response dots placed 8° to the left and right of fixation. The direction of motion was equally likely to be rightward or leftward, and the strength of motion was randomly selected from 9 values between 0 and 40% coherence. Subjects were instructed to fixate until they could judge the direction of motion, and to indicate their choice by moving their eyes to the response dot in the same direction as the judged motion. Subjects received auditory feedback about their choice after each trial. We measured saccades on each trial to examine the subjects' reaction times as well as their choices.
As expected, autistic subjects showed higher motion coherence thresholds (15–32%) compared to control subjects (10–13%). However, the reaction times for autistic subjects were also much shorter (∼250 ms) than for controls (∼500 ms). In addition, the reaction times for the autistic subjects did not change as a function of signal strength, unlike the control subjects, who showed significantly shorter reaction times for stronger motion signals.
Our results confirm that autistic subjects have higher thresholds for discriminating motion direction, consistent with possible abnormalities in sensory processing. However, the unusual pattern of reaction times in the task suggests that the process of forming the perceptual choice is also atypical.
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