Susceptibility to Ebbinghaus and Muller-Lyer illusions in autistic children: a comparison of three different methods

Catherine Manning, Michael J. Morgan, Craig T. W. Allen, Elizabeth Pellicano

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)


Background: 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.

Methods: We measured susceptibility to two contextual illusions (Ebbinghaus, Muller-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.

Results: Across all tasks, autistic children were equally susceptible to the Ebbinghaus illusion as typically developing children. Autistic children showed a heightened susceptibility to the Muller-Lyer illusion, but only in the method-of-adjustment task. This result may reflect differences in decisional criteria.

Conclusions: 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.

Original languageEnglish
Article number16
Pages (from-to)16
Number of pages1
JournalMolecular Autism
Publication statusPublished - 23 Mar 2017


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