Retinal and cortical patterns of spatial anisotropy in contrast sensitivity tasks.

It has often been postulated that asymmetries in performance within the visual field (VF) are not characteristic of early visual processing. Here, human retinal (naso/temporal), cortical (left/right) and superior/inferior patterns of asymmetry were explored with achromatic contrast sensitivity (CS) tasks, that probed distinct spatiotemporal frequency channels. Low spatial, high temporal frequency stimuli (illusory frequency-doubling (FD)) yielded superior and temporal field disadvantage. Independent right and nasal visual hemifield patterns of disadvantage were found when probing an intermediate spatial frequency (ISF) channel, with stationary sinusoidal gratings. These findings show that asymmetries in spatial vision are explained by independent retinal and cortical mechanisms.