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Spatial suppression in visual motion perception is driven by inhibition: Evidence from MEG gamma oscillations
Spatial suppression (SS) is a visual perceptual phenomenon that is manifest in a reduction of directional sensi-
tivity for drifting high-contrast gratings whose size exceeds the center of the visual field. Gratings moving at faster
velocities induce stronger SS. The neural processes that give rise to such size- and velocity-dependent reductions
in directional sensitivity are currently unknown, and the role of surround inhibition is unclear. In magneto-
encephalogram (MEG), large high-contrast drifting gratings induce a strong gamma response (GR), which also
attenuates with an increase in the gratings’ velocity. It has been suggested that the slope of this GR attenuation is
mediated by inhibitory interactions in the primary visual cortex. Herein, we investigate whether SS is related to
this inhibitory-based MEG measure. We evaluated SS and GR in two independent samples of participants: school-
age boys and adult women. The slope of GR attenuation predicted inter-individual differences in SS in both
samples. Test-retest reliability of the neuro-behavioral correlation was assessed in the adults, and was high be-
tween two sessions separated by several days or weeks. Neither frequencies nor absolute amplitudes of the GRs
correlated with SS, which highlights the functional relevance of velocity-related changes in GR magnitude caused
by augmentation of incoming input. Our findings provide evidence that links the psychophysical phenomenon of
SS to inhibitory-based neural responses in the human primary visual cortex. This supports the role of inhibitory
interactions as an important underlying mechanism for spatial suppression.