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


RESULTS
Across all tasks, autistic children were equally susceptible to the Ebbinghaus illusion as typically developing children. Autistic children showed aheightenedsusceptibility to the Müller-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.
Department of Experimental Psychology, University of Oxford, 9 South Parks Road, Oxford, OX1 3UD UK.
Catherine
0000-0001-6862-2525
C
Manning
Applied Vision Research Centre, City University, Northampton Square, London, EC1V 0HB UK.|Max-Planck Institute for Metabolism Research, Gleueler Str. 50, 50931 Köln, Germany.
Michael J
MJ
Morgan
Centre for Research in Autism and Education (CRAE), UCL Institute of Education, University College London, 55-59 Gordon Square, London, WC1H 0NU UK.
Craig T W
CTW
Allen
Centre for Research in Autism and Education (CRAE), UCL Institute of Education, University College London, 55-59 Gordon Square, London, WC1H 0NU UK.|School of Psychology, University of Western Australia, 35 Stirling Highway, Perth, WA 6009 Australia.
Elizabeth
E
Pellicano
D000293:Adolescent; D001321:Autistic Disorder / Q000523:psychology*; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D009903:Optical Illusions / Q000502:physiology*; D010364:Pattern Recognition, Visual; D010775:Photic Stimulation / Q000379:methods*; D012858:Size Perception
Autism; Cognitive bias; Context; Global processing; Perception; Response bias; Vision; Visual illusions