The online version of this article (doi:10.1186/s13229-017-0127-y) contains supplementary material, which is available to authorized users.
Studies reporting altered susceptibility to visual illusions in autistic individuals compared to that typically developing individuals have been taken to reflect differences in perception (e.g. reduced global processing), but could instead reflect differences in higher-level decision-making strategies.
We measured susceptibility to two contextual illusions (Ebbinghaus, Müller-Lyer) in autistic children aged 6–14 years and typically developing children matched in age and non-verbal ability using three methods. In experiment 1, we used a new two-alternative-forced-choice method with a roving pedestal designed to minimise cognitive biases. Here, children judged which of two comparison stimuli was most similar in size to a reference stimulus. In experiments 2 and 3, we used methods previously used with autistic populations. In experiment 2, children judged whether stimuli were the ‘same’ or ‘different’, and in experiment 3, we used a method-of-adjustment task.
Across all tasks, autistic children were equally susceptible to the Ebbinghaus illusion as typically developing children. Autistic children showed a heightened susceptibility to the Müller-Lyer illusion, but only in the method-of-adjustment task. This result may reflect differences in decisional criteria.
Our results are inconsistent with theories proposing reduced contextual integration in autism and suggest that previous reports of altered susceptibility to illusions may arise from differences in decision-making, rather than differences in perception per se. Our findings help to elucidate the underlying reasons for atypical responses to perceptual illusions in autism and call for the use of methods that reduce cognitive bias when measuring illusion susceptibility.
Additional file 1: Results with no replacement of outliers. Means, standard deviations and t-test statistics for group differences in bias in the Ebbinghaus and Müller-Lyer tasks in experiment 1 and Müller-Lyer context-free judgments in experiment 3 when outliers were not replaced. (PDF 9 kb)13229_2017_127_MOESM1_ESM.pdf
Additional file 2: Results of robustness checks for Bayesian analyses. Results of robustness checks for Bayesian independent sample t tests in experiments 1 and 3 and for the Bayesian contingency test in experiment 2. (PDF 92 kb)13229_2017_127_MOESM2_ESM.pdf
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- Susceptibility to Ebbinghaus and Müller-Lyer illusions in autistic children: a comparison of three different methods
Michael J. Morgan
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- BioMed Central