Blindsight following visual cortex deafferentation disappears with purple and red stimuli: a case study.

We employed a redundant signal effect (RSE) paradigm to ascertain the role of the superior colliculus (SC) in blindsight. The RSE consists of the speeding of reaction time (RT) to double versus single stimuli. One patient with a unilateral lesion of the optic radiation and consequent hemianopia showed a RSE with pairs of visual stimuli presented across the vertical meridian despite seeing only stimuli in the intact hemifield. However, when, instead of achromatic stimuli we used short or long wavelength stimuli the implicit RSE disappeared. This result raises the possibility that implicit chromatic processing in the affected hemifield might have a different neural substrate following deafferentation with respect to lesion of the primary visual cortex.