Contrast sensitivity: a fundamental limit to vision restoration after V1 damage.

Stroke-induced V1 damage in adult humans induces a rapid and severe impairment of contrast sensitivity for orientation and direction discrimination in the affected hemifield, although discrimination of high-contrast stimuli can persist for months. Adaptive training with Gabor patches of progressively lower contrasts improves contrast sensitivity for these discriminations in the blind-field of both subacute (<3 months post-stroke) and chronic (>6 months post-stroke) participants, although it fails to restore fully-normal contrast sensitivity. Nonetheless, more subacute than chronic stroke participants benefit from such training, particularly when discriminating the orientation of static, non-flickering targets. Thus, contrast sensitivity appears critically dependent on processing within V1, with perceptual training displaying limited potential to fully restore it after V1 damage.