Registration of light stimuli in the cortically blind hemifield and its effect on localization.

Patients who suffer from unilateral damage to the geniculostriate system were asked to make a voluntary blink response whenever they guessed that a light stimulus was presented in their perimetrically blind hemifield. After about 600 trials they were able to register the presence of a light stimulus appearing in the 'blind' part of their visual field without any conscious visual access and, additionally, without any link to correct verbal responses. The patients' ability to localize targets presented in the hemianopic part of the visual field was at a high level of accuracy (as judged by their saccadic responses) after this procedure. The results indicate that there is a common extrastriate visual pathway subserving the performance in registration and localization of visual stimuli.