Abstract
BACKGROUND: 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 controls, but the mechanisms underlying this difference are poorly understood. METHODS: We assessed perceptual and neural surround suppression in 38 controls, 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 7 tesla fMRI responses in the lateral geniculate nucleus (LGN), primary visual cortex (V1), and lateral occipital complex (LOC). Additionally, we measured the concentration of γ-aminobutyric acid (GABA; an inhibitory neurotransmitter) in occipital cortex using 7 T MR spectroscopy. RESULTS: Responses in LOC showed the expected effect of weaker surround suppression in PwPP (and relatives) versus controls. 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. Multi-voxel pattern analysis of V1 fMRI responses revealed a group difference in decoding Surround vs. No Surround, with a trend toward lower accuracy in PwPP vs. controls. CONCLUSIONS: Our results suggest subtle differences in visual center-surround processing among people with psychotic psychopathology. Possible explanations for the discrepancy with previous findings include differences in task design and the deployment of spatial attention across groups.