There are anecdotal accounts of blind people who can see sometime and deaf people who can likewise hear. In the 1970s, Larry Weiskrantz was working with brain damaged subjects who could not consciously see an object in front of them in certain places within their field of vision. Yet when asked to guess if a light had flashed in their region of blindness, the subjects "guessed" right at a probability much above that of chance.

In a typical case the subjects is completely blind in the left or right visual field after undergoing brain surgery yet he performs very well in reaching for objects. "Needless to say, [the patient DB] was questioned repeatedly about his vision in his left-half field, and his most common response was that he saw nothing at all...When he was shown the results, he expressed surprise and insisted several times that he thought he was just 'guessing.' When he was shown a video film of his reaching and judging orientation of lines, he was openly astonished." Obviously, blindsight patients possess visual ability but it is not part of their conscious awareness.

Blindsight has been explained as being a process similar to that of implicit memory or it has been proposed that consciousness is a result of a dialog going on between different regions of the brain. When this dialog is disrupted, even if the sensory signals do reach the brain, the person will not be aware of the stimulus. In visual processing, it appears that motion and form are processed separately, in parallel.

Greenfield has proposed that blindsight might be a result of the incoming signals being too weak due to some inhibitory chemical process. Flohr has suggested that consciousness depends not so much on the extent of neurons recruited but, rather, on the the rate at which the recruitment occurs. This rate of recruitment may be inhibited due to some inhibitory process.

These explanations of blindsight in terms of the dialog within the regions V1 and V5 or neurons recruited therein do not exclude the possibility that simulta-neous activity in other regions is essential for the feeling of consciousness. These simultaneous activity elsewhere need not be synchronized with the oscillations in the V1 and V5 regions.

Greenfield summarizes: "We have two clues about the phenomenology of consciousness; first, that it depends on a focus that is literally or psychologically strong, and second, that it might depend spatially and/or temporally on the extensive, rapid recruitment of a population of brain cells. These brain cells would span different brain regions or different parts of the cortex to constitute a temporary working assembly where all member neurons resonated or discharged in the same way. The more powerful the recruiting signal, the greater the likelihood that such assemblies would be established and consciousness ensue."

This model is quite attractive but it has fundamental difficulties. First, the blindsight patient is conscious although he may not be conscious of certain images in his field of vision. Second, there are activities which are performed automatically of which we are not conscious. Some of these can be brought under the ambit of conscious control with varying degree of difficulty. As examples consider breathing or heartbeats, of which breathing is easily controlled and heartbeats can be controlled only by yogic adepts.

Why not consider that the injury in the brain leading to blindsight causes the vision in the stricken field to become automatic? Then through retraining it might be possible to regain the conscious experience of the images in this field. In the holistic explanation, the conscious awareness is a correlate of the activity in a complex set of regions in the brain. No region can be considered to be producing the function by itself although damage to a specific region will lead to the loss of a corresponding function.