BLINDSIGHT REVISITED

Some human patients with lesions to their primary visual (striate) cor tex (V1) demonstrate residual visual capacity, but without acknowledge d perceptual awareness. This phenomenon has been termed blindsight. Re cent results from work on blindsight patients suggest that it is unlik ely to be attributable to intact residual areas (tags) of V1. Previous research has reported that blindsight patients can retain the ability to detect monochromatic light and grating stimuli, and to discriminat e orientation and direction of movement in their 'blind' fields. These findings have been joined by reports that these patients also are sen sitive to, and are able to discriminate, wavelength in the absence of any experience of 'colour'. This reveals that retinal pathways other t han those to the striate cortex are crucially involved in vision. Cond itions can be controlled for obtaining either acknowledged awareness o r unawareness of discrimination of the direction of a small moving tar get in blindsight patients. This potentially offers the possibility to determine whether there are structures uniquely involved in visual aw areness. Monkeys lacking V1 also clearly demonstrate residual visual c apacity, and some evidence exists that they also experience 'blindsigh t'.