Residual vision in a subject with damaged visual cortex

It is well known that a lesion in the optic radiation or striate cortex lea ds to blind visual regions in the retinotopically corresponding portion of the visual field. However, various studies show that some subjects still pe rceive certain stimuli even when presented in the "blind" visual field. Suc h subjects either perceive stimuli abnormally or only certain aspects of th em (residual vision) or, in some cases, deny perception altogether even tho ugh visual performance can be shown to be above chance (blindsight). Resear ch on monkeys has suggested a variety of parallel extrastriate visual pathw ays that could bypass the striate cortex and mediate residual vision or bli ndsight. In the present study, we investigated a subject with perimetricall y blind visual areas caused by bilateral brain damage. Black and white stim uli were presented at many locations in the intact and affected areas of th e visual field. The subject's task was to state, using confidence levels, w hether the target stimulus was black or white. The results revealed an area in the "blind" visual field in which the subject perceived a light flash w hen the experimental black stimulus was presented. We hypothesize that a sp ared region in the visual cortex most likely accounts for these findings.