Introduction. Visual illusions are used increasingly as a practical and eff ective tool for
studying the underlying mechanisms of perception in the normal and morbid conditions.
Understanding the organization of perception can help in the study of the causes of
schizophrenia symptoms.
Purpose. To identify the susceptibility to visual illusions (Muller-Lyer and Ponzo) of
schizophrenic patients (resistant and non-resistant to treatment) compared to healthy
controls in visual and motor estimation.
Materials and methods. Three groups of subjects participated in the cross-sectional study:
9 resistant patients with schizophrenia, 14 non-resistant patients with schizophrenia, and
20 healthy subjects. The participants performed three types of tasks: memorization of
tracing movements across the central shafts of illusory or neutral stimuli on the sensory
screen, reproduction of memorized movements and verbal adjustment of the central
shafts of two stimuli by the keyboard.
Results. In the adjustment task, both illusions are signifi cantly stronger in the resistant
group than in the healthy control one. The sensorimotor estimations of neutral stimuli as well as the Ponzo illusion do not diff er from zero at the memorization phase in all three
groups. The Muller-Lyer illusion diff ers signifi cantly from zero in each group during the
memorization phase and during the reproduction phase. The Ponzo illusion exists in all
three groups, and is signifi cantly weaker for the healthy control group than for the nonresistant and for the resistant groups.
Conclusion. The increased sensitivity to illusions compared to healthy controls detected
in both tasks (adjustment and tracing) indicates impairments in the ventral and dorsal
visual pathways in schizophrenic patients.well as the Ponzo illusion do not diff er from zero at the memorization phase in all three
groups. The Muller-Lyer illusion diff ers signifi cantly from zero in each group during the
memorization phase and during the reproduction phase. The Ponzo illusion exists in all
three groups, and is signifi cantly weaker for the healthy control group than for the nonresistant and for the resistant groups.
Conclusion. The increased sensitivity to illusions compared to healthy controls detected
in both tasks (adjustment and tracing) indicates impairments in the ventral and dorsal
visual pathways in schizophrenic patients.