Center-Surround Processing in Psychosis

People with psychotic psychopathology (PwPP) often experience subtle variations in visual perception. In the contrast-surround suppression illusion, a central pattern appears to have lower contrast in the presence of a surrounding pattern. PwPP typically show weaker contrast-surround suppression than control participants, but the mechanisms underlying this difference are poorly understood.

We assessed perceptual and neural surround suppression in 38 control participants, 44 first-degree biological relatives of PwPP, and 64 PwPP as part of the Psychosis Human Connectome Project. To probe the neural mechanisms of surround suppression, we quantified contrast discrimination thresholds and examined 7T functional magnetic resonance imaging (fMRI) responses in the lateral geniculate nucleus, primary visual cortex (V1), and lateral occipital complex (LOC). Additionally, we measured the concentration of GABA (gamma-aminobutyric acid), an inhibitory neurotransmitter, in the occipital cortex using 7T MR spectroscopy.

Responses in the LOC showed the expected effect of weaker surround suppression in PwPP (and relatives) compared with control participants. However, in V1, we found no group differences in surround suppression strength. Additionally, we saw no behavioral evidence for reduced surround suppression in PwPP. Suppression metrics were not significantly correlated with occipital GABA levels or symptom measures. Multivoxel pattern analysis of V1 fMRI responses revealed a group difference in decoding surround versus no surround, with a trend toward lower accuracy in PwPP compared with control participants.

Our results suggest subtle differences in visual center-surround processing among PwPP. Possible explanations for the discrepancy from previous findings include differences in task design and the deployment of spatial attention across groups.