Müller-Lyer illusion susceptibility is conditionally predicted by autistic trait expression

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Tailor, Ganesh
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The Müller-Lyer Illusion (ML) is a visual illusion that biases size estimation. Illusory bias can be assessed using a variety of methods that may lead to different degrees of bias. There is also some evidence autistic individuals are less likely than neurotypicals to perceive illusory biases that rely on environmental experience. Varying levels of autistic trait expression have also been proposed to modulate susceptibility to illusions. The Autism Quotient (AQ) and Systemizing Quotient (SQ) are self-report measures that quantify autistic trait expression and systemizing ability in neurotypicals. The current study aimed to determine if perceptions of illusory size bias negatively correlate with autistic trait expression and the extent to which varying methods of illusion presentation change the magnitude of illusory bias. Thirty neurotypical adults completed both questionnaires as well as four size estimation tasks. Tasks 1 and 2 involved perceptual discrimination of ML figures by concurrent and successive presentation, where participants selected the longer figure by button press. In Task 3 participants adjusted the size of a non-illusory line to match its size to an illusory target ML figure. For Task 4 participants adjusted a composite ML figure to match its size to the target ML figure. Overall, task performance was not correlated with autistic trait expression. The one exception was a positive correlation with AQ when adjusting a composite illusory ML figure in Task 4. There was a stronger bias found in the concurrent figure presentation (Task 1) and composite figure adjustments (Task 4) when compared to the successive presentation used in Task 2 and the non-illusory adjustment in Task 3. Given these results, illusion susceptibility to the ML is suggested to be reduced with increases in AQ, but only when the method of illusion measurement is adjustment of concurrent illusory figures. Taken together the results provide evidence that traits associated with autism in a neurotypical population may systematically modulate perception.
Müller-Lyer, Autism, Perception action, Magnitude estimation, Illusion susceptibility, Autism-spectrum quotient, Visual illusion, Visual perception