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Abstract:
Blindsight is the term coined by Weiskrantz (see Weiskrantz
et al. 1974) to describe the condition in which subjects with
damage to their primary visual cortex are able to perform simple
visual tasks in the area of visual space corresponding to their
brain-damage while maintaining that they have no visual experience
there. In other words, they retain some visual abilities in an area
where they report that they are phenomenally blind. This
dissociation between conscious experience and visual performance is
usually revealed in forced-choice tasks involving discriminations
of simple stimulus properties such as location, contrast,
orientation, color and so on. However, while conducting an
experiment mapping the area of one subject's residual vision
(Kentridge et al. 1997), we recently chanced upon an exception. In
this experiment the subject had to decide which of two tones was
accompanied by a flashing spot of light. By examining how his
performance varied as the spot of light was presented in different
positions we could map the area over which his blindsight extended.
Quite by chance, during one of the breaks in testing the subject
(known as GY) remarked that he had just realised that the stimuli
were sometimes being presented well above the horizontal and so now
he was trying to pay attention higher up in his blind visual field.
This is an extraordinary remark since one's intuition is that it is
attention that gives rise to consciousness. Our subjective
experience is that we are most conscious of that part of the world
to which we are attending. This apparently close relationship
between attention and consciousness was remarked upon from the
birth of modern psychology (see, for example, James [1890], Wundt
[1912] and still influences many modern theories of consciousness.
We followed the observation up in a series of experiments designed
to establish exactly which aspects of attention continue to
function in the blind region of GY's visual field. These
experiments are reported in detail elsewhere (Kentridge et al.,
submitted), in the present chapter we will briefly summarize their
results and then consider their implications for theories of
consciousness and the central bases of visual attention.
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