Objectives:
The aim of the study was an assessment of the phenomenon of depth perception in schizophrenic patients compared to healthy subjects.

Methods:
We conducted a comparison erroneous assessment of the concave side of the mask as convex, using the popular website presenting rotating Charlie Chaplin’s mask. The study was performed in patients hospitalized at the Stanisław Kryzan Psychiatric Hospital in Starogard Gdanski diagnosed with paranoid and undifferentiated schizophrenia based on ICD-10 criteria and control group matched for age and education; each group included 58 subjects.

Results:
The correct perception of depth in the hollow mask illusion regards approx. 30% of patients with paranoid and undifferentiated schizophrenia during exacerbation and it is three times higher in this group than in the general population. Except the number of relapses and hospitalization in anamnesis, it shows no correlation with another clinical and demographic data such as: the age of onset, the duration of illness, and results on Positive and Negative Syndrome Scale (PANSS).

Conclusions:
The correct perception of the hollow mask may be potentially one of the subsequent premises for the diagnosis of schizophrenia in doubtful cases. The simplicity and general availability is also an argument for conducting the test.