Research in the literature suggests that patients with schizophrenia are particularly susceptible to the Müller-Lyer illusion and consider it a potential marker of vulnerability.

We hypothesized that the perception of the Müller-Lyer illusion might be influenced by the patient's mental state. To test this, we studied 12 patients with schizophrenia, aged 18 to 45 years, at both the second week (after the patient became available for contact and could perform cognitive tests) and the eighth week of therapy. Participants were asked to align two segments on a monitor screen to match in length. They were presented with both neutral segments of equal length and segments configured to produce the Müller-Lyer illusion.

Mental state was assessed using the PANSS scale. Only patients with positive symptom scores of less than 4 points were included in the study. Statistical analysis was conducted using a mixed regression model.

The study results indicated no significant differences in perception between patients at the second and eighth weeks of therapy, suggesting that the mental state during this period did not substantially influence the course of therapy. Our findings suggest that the perception of the Müller-Lyer illusion is not significantly influenced by the severity of the mental state, and that antipsychotic therapy does not appear to impact cognitive functions related to susceptibility to the Müller-Lyer illusion.

Financial statement: This work was supported by a grant from the Russian Science Foundation (project No. 22-18-00074) "Psychological mechanisms of perception and action mismatch when solving tasks under visual illusions”.