A very different slant on orientation sensitivity in human and non-human primates

Abstract

It is generally assumed that sensitivity to different stimulus orientations is mapped in a globally equivalent fashion across primate visual cortex, at a spatial scale larger than that of orientation columns. However earlier evidence, and a new model, predicts instead that radial orientations should produce higher activity than other orientations, throughout visual cortex. Here this prediction was robustly confirmed using human psychophysics, human fMRI, and fMRI in behaving macaque monkeys. In both human and macaque cortex, fMRI activity was higher in the retinotopic representations of polar angle which corresponded to the radial stimulus orientations. In a global demonstration of this, we activated complementary retinotopic quadrants of visual cortex by simply changing stimulus orientation - without changing the stimulus location in the visual field. This radial bias was also robust in psychophysical tests, using analogous stimuli. All this evidence confirms a novel link between orientation sensitivity and the cortical retinotopy, which have previously been considered independent.