Abstract
Goal. A central question in neuroscience is how the organisation of cortical maps relates to perception, for which primary visual cortex (V1) is an ideal model system. V1 nonuniformly samples the retinal image, with greater cortical magnification (mm2 of cortex per deg2 of visual field) at the fovea than periphery, and at the horizontal than vertical meridian. V1 size and cortical magnification greatly vary across individuals - this variation should have important consequences for visual perception. Methods. We united fMRI with psychophysics to quantify individual differences in the organisation of V1 with contrast sensitivity at the four polar angle meridians. In 29 observers, we employed an orientation discrimination task to measure contrast sensitivity at the four cardinal meridians and, in the same observers, used fMRI to measure their V1 maps. We calculated overall V1 size, and the amount of V1 surface area dedicated to processing the same angular locations as the contrast measurements. Across observers, we correlated contrast sensitivity with V1 measurements. Results. First, contrast sensitivity (averaged across locations) was positively correlated with the size of V1 (r=0.47); observers with higher contrast sensitivity had a larger V1. Second, contrast sensitivity was positively correlated with the amount of surface area dedicated to the corresponding meridian (r=0.60); higher contrast sensitivity was associated with greater dedicated local surface area. Third, we computed the horizontal-vertical meridian asymmetry for contrast sensitivity and V1 surface area. The two measures were correlated (r=0.60); a stronger horizontal-vertical asymmetry in contrast sensitivity corresponded to a stronger horizontal-vertical asymmetry in the distribution of V1 surface. Conclusions. These data reveal that individual differences in contrast sensitivity are linked to individual differences in V1 surface area at global and local scales, and more broadly, show that differences in visual perception are rooted in the organisation of V1.