Visual illusions provide a unique opportunity to understand cognitive and perceptual
alterations in schizophrenia-spectrum conditions. Schizophrenia patients often exhibit
increased susceptibility to the Müller-Lyer illusion. Here, we investigate susceptibility
to the Müller-Lyer visual illusion in the general population with different levels
of schizotypy.We assessed a population-based convenience sample (N = 263) on an online
platform. In addition to basic demographics, participants completed the Müller-Lyer
illusion, the Cardiff Anomalous Perceptions Scale (CAPS) to measure perceptual anomalies,
and the Multidimensional Schizotypy Scale - Brief (MSS-B) for schizotypic traits.
To evaluate what predicts susceptibility to the illusion, we fitted a large set of
multilevel logistic regression models and performed model averaging over the coefficients.We
found support for increased illusion susceptibility among individuals with high positive
schizotypy. However, we did not find a comparable effect for anomalous perceptions
alone, or for negative or disorganized schizotypy.The increased Müller-Lyer effect
in positive schizotypy might be specific to delusion-like beliefs and magical ideation.
Further research is needed to clarify how a hierarchical Bayesian formulation of brain
function (e.g. imbalances between bottom-up perceptual processing and substantial
reliance on prior expectations) can account for the Müller-Lyer effect in schizophrenia-spectrum
conditions.
