Reduced visual orientation-surround suppression in schizophrenia shown by measuring contrast detection thresholds

Abstract

The contrast detection threshold for a grating located in the visual periphery is increased by the presence of a surrounding grating of the same spatial frequency and orientation. This inhibition has been termed orientation-surround suppression. Previous studies (Yoon et al., 2009, Schizophrenia Bulletin, 35,6) using contrast discrimination thresholds, have suggested abnormal surround suppression in patients with schizophrenia. In this work, we have tested this hypothesis by measuring contrast detection thresholds using different stimulus configuration (Serrano-Pedraza, Grady, & Read, 2012, Journal of Vision, 12(6)). We tested two groups: 21 patients with schizophrenia and 44 healthy control subjects. To obtain the contrast thresholds, we used Bayesian adaptive staircases in a 4AFC detection task where the target was a grating within a 3 deg Butterworth window that could appear in one of four possible positions at 5 deg eccentricity. We compared three experimental conditions, a) target with no surround (NS), b) target on top of a surrounding grating of 20 deg diameter and 25% contrast with same spatial frequency and orthogonal orientation (OS), and c) target on top of a surrounding grating with parallel (same) orientation (PS). Our results show significantly lower thresholds for controls than for patients in NS and OS conditions (t-test, p<0.001). We also found significant differences between groups when comparing suppression ratios PS/NS of contrast thresholds (p<0.001). To examine whether the difference in PS/NS was driven by the lower NS thresholds for controls, we also examined a subgroup chosen such that patients and controls had similar NS thresholds. This subgroup showed significant differences between patients and controls in both PS (p=0.0167) and PS/NS (p=0.0105). Both these analyses therefore indicate that a parallel surround raised contrast thresholds less in patients than in controls. Our results support the hypothesis that inhibitory lateral connections in early visual cortex are impaired in schizophrenia patients.

Meeting abstract presented at VSS 2014