Differential pupillary constriction and awareness in the absence of striate cortex

The fact that the pupil constricts differentially to visual stimuli in the absence of changes in light energy makes it a valuable tool for studying no rmal function as well as residual capacity in hemianopic subjects. When pup illometrically effective stimuli such as equiluminant gratings or coloured patches with an abrupt onset and offset are presented to the 'blind' hemifi eld, a hemianopic subject with damage largely restricted to striate cortex (V1) sometimes reports being 'aware' of the transient onset/offset, althoug h without 'seeing' as such. The question addressed here is whether the pupi l still responds in the condition of blindsight in its strict sense-i.e. di scriminative capacity in the absence of acknowledged awareness-when stimuli are deliberately designed to eliminate awareness. This was accomplished by making stimulus onset and offset slow and gradual. The results with a well -studied hemianope, G.Y., demonstrate that there is still a pupillary const riction to isoluminant achromatic gratings and red-coloured stimuli, althou gh reduced in size, in the absence of acknowledged awareness.