Blindsight in normal observers.
Some patients with lesions in visual cortex lack conscious visual experience but, when tested, exhibit a significant ability, termed 'blindsight', to discriminate visual stimuli. Here we report two different visual displays that induce blindsight in normal observers. Using an objective measure, we show that conscious experience remains defective at presentation times much longer (1 s) than the onset of visual sensitivity (approximately 60 ms). To obtain this effect, we generate a contrast between visual textures and then conceal the contrast by superimposing 'complementary' textures. Complementarity can involve either opposite motion or binocular rivalry and orthogonal orientation. In both cases, observers locate the texture contrast reliably but do not, by either subjective or objective measures, consciously experience it. Taken together with present knowledge of the visual cortical site(s) at which opposite motion and rivalrous orientation interact, this observation bears upon the functional anatomy of conscious visual experience.
Kolb
F C
FC
Computation and Neural Systems 139-74, California Institute of Technology, Pasadena 91125, USA.
Braun
J
J
D015350:Contrast Sensitivity; D006801:Humans; D009898:Optic Disk / Q000502:physiology*; D011601:Psychophysics; D014793:Visual Cortex / Q000502:physiology* / Q000503:physiopathology