Reduced contrast surround suppression associated with schizophrenia depends on visual acuity and scene context

Abstract

Perceptual distortions are a primary symptom of schizophrenia. One perceptual distortion that has strong potential for revealing how neural networks function differently in the brains of people with psychotic disorders is an impairment of contrast surround suppression. Contrast surround suppression is the reduction of the perceived contrast of a visual stimulus when it is surrounded by a similar texture; a reduction that is not as strong for people with schizophrenia, compared to neurotypical controls. Contrast surround suppression is generally measured with a low-contrast target embedded in a high-contrast surround. In the present paradigm, however, the contrast of the center and surround were matched. This was done to remove one bottom-up segmentation cue (contrast difference), with the goal of better isolating the neural mechanisms responsible for atypical surround suppression in psychosis. Instead, we varied only the relative orientation of the target and surround textures, to quantify the impact of this segmentation cue. We examined how the degree and form of psychopathology were related to abnormal suppression by studying people with schizophrenia (N=31) and bipolar disorder (N=29), first-degree biological relatives of both patient groups (N=28, N=21, respectively), and healthy controls (N=29). Contrast surround suppression deficits in schizophrenia, while robustly observable under many stimulus conditions, were absent under the condition that produced strongest suppression: a high-contrast parallel grating with a high-contrast surround. The expected reduced suppression for participants with schizophrenia was only present when target and surround orientations were not parallel and, intriguingly, was only present for participants with relatively worse acuity. Our findings help elucidate the perceptual mechanisms of impaired center-surround processing in schizophrenia and highlight the importance of recent reports showing altered retinal function in this disorder.