The blindsight saga

Blindsight is the ability of patients with clinically blind field defects, caused by damage to the primary visual cortex V, to detect, localise and even discriminate visual stimuli that they deny seeing. Blindsight tells us much about the nature of visual processing in the absence of the primary visual cortex and is a paradigmatic example of implicit knowledge. It has attracted widespread interest and debate amongst philosophers, cognitive neuropsychologists and visual neuroscientists. Its downside is that possible artefacts abound, much more so than with examples of implicit memory or deaf hearing and numb touch. Unfortunately the artefacts are still frequently ignored, or dismissed as captious, with the result that many of the genuine qualities of blindsight remain uncertain. Now that blindsight in monkeys has been established the substantial literature on the effects of removing parts or all of V1 in monkeys on the residual physiological cerebral responses to visual stimuli in their field defects is at last directly relevant to human blindsight. Whether blindsight is, or could be, useful in everyday life is the next unsolved problem.