The Hermann grid illusion fails to fool patients with schizophrenia: Experimental support for a reduced lateral inhibition hypothesis

Abstract

A large body of evidence indicated that patients with schizophrenia spectrum disorders show deficit in perceptual and visual processing, but little is known about the origin of this defect. One of the strategies used to reveal the origin of such defects is to use tests that have a strong neuropsychological basis in normal individuals. In this study, we used the Hermann grid task to reveal the source of visual deficit in patients with schizophrenia. Several findings have shown that the Hermann grid illusion results from lateral inhibition of neuro-visual pathway cells. We compared 26 patients with schizophrenia to 26 participants with high schizotypy traits and 26 normal controls in a computer test we designed for the Hermann grid illusion. Chi-square analysis revealed that the patients with schizophrenia and the participants with high schizotypy traits reported significantly less the Hermann grid illusion than healthy controls. Therefore, the results support the hypothesis of a defect in lateral inhibition of patients with schizophrenia. This might suggest that the visual pathway cells in schizophrenic patients failed to properly combine the data from the visual receptors as they do in healthy people. • The Hermann grid illusion has wealthy neuropsychological background. • Visual perception difficulties in schizophrenia have been always reported. • Patients with schizophrenia do not report the Hermann grid illusion. • Evidence show that lateral inhibition contributes in the Hermann grid illusion. • Lack of Hermann grid illusion support a lateral inhibition defect in schizophrenia.