Intact Susceptibility to Visual Illusions in Autistic Individuals

Altered sensory perception, a core characteristic of autism, has been attributed to attenuated use of stimuli context or prior information in perception. Reduced susceptibility to perceptual illusions was extensively used to support these accounts for autistic perception. However, empirical evidence has been inconsistent. The current study systematically investigated susceptibility to size illusions in autistic and non-autistic individuals using a standardized psychophysical battery. Eighty-one participants, 41 autistic and 40 non-autistic individuals, completed the Ben-Gurion University Test for Perceptual Illusions (BTPI), measuring susceptibility to the Ponzo, Ebbinghaus, and Height-width illusions. The results demonstrate clear evidence for susceptibility to illusions in the perception of size both in the autistic and non-autistic groups. No significant differences were found between groups in the magnitude of illusion on the perceived size, or on the perceptual resolutions of size (discrimination thresholds) in any of the illusory settings tested. The results challenge current theories suggesting reduced reliance on priors or enhanced sensory measurement in autism. Instead, using robust psychophysical methods, the study provides clear evidence for autistic people forming priors and using long-term knowledge in perception.