Abstract
Perceptual surround suppression is a phenomenon in which the perceived contrast of a stimulus is reduced when accompanied by a surrounding stimulus. This effect is influenced by various stimulus features of the center-surround, including relative orientation (i.e., orientation-dependent surround suppression [ODSS]). Patients with schizophrenia (SZ) often exhibit reduced ODSS, though the neurophysiological correlates of this atypical perception are not yet fully understood. Accordingly, the present study examined differences in electrophysiological (EEG) response between SZ (N=28), healthy controls (HC;N=26), patients with bipolar disorder (BP;N=29) and first-degree relatives of both patient groups (SZR,BPR;N=25,N=19) to probe whether atypical neural functions during ODSS are related to severe mental illness more broadly, and/or mark genetic liability for psychosis. Participants indicated whether a circular grating with a surrounding annulus randomly set to one of five relative orientations, or a reference grating with no surround, had greater perceived contrast, while undergoing 126-channel EEG recording. We applied current source density interpolation to more accurately capture contralateral visual cortical activation within group-averaged visual evoked potentials. Visual P1 (50-140 ms; reflects low-level visual processing) was insensitive to orientation, with SZ demonstrating markedly reduced amplitudes; BP and SZR exhibited intermediate reductions. The N1 component (120-205 ms; related to visual discrimination) was modulated by surround orientation, and attenuated in SZ and BPR. Blunted P1 response was associated with greater psychotic psychopathology, whereas blunted N1 was associated with reduced perceptual suppression. Experimental results suggest that early neural functions reflecting basic visual processing are disrupted in severe mental illness, and associated with genetic liability for psychosis—these disruptions were greatest in SZ, and associated with dimensional aspects of psychotic psychopathology. This study highlights that SZ exhibit alterations in orientation-selective neural functions that relate to reduced perceptual suppression, yielding novel insights into the neurophysiological mechanisms underlying reduced ODSS in SZ.