Blindsight

Blindsight is the ability of people who are cortically blind due to lesions in their striate cortex, also known as primary visual cortex or V1, to respond to visual stimuli that they do not consciously see. The majority of studies on blindsight are conducted on patients who have the "blindness" on only one side of their visual field. Following the destruction of the striate cortex, patients are asked to detect, localize, and discriminate amongst visual stimuli that are presented to their blind side, often in a forced-response or guessing situation, even though they don't consciously recognise the visual stimulus. Research shows that blind patients achieve a higher accuracy than would be expected from chance alone. Type 1 blindsight is the term given to this ability to guess—at levels significantly above chance—aspects of a visual stimulus (such as location or type of movement) without any conscious awareness of any stimuli. Type 2 blindsight occurs when patients claim to have a feeling that there has been a change within their blind area—e.g. movement—but that it was not a visual percept. Blindsight challenges the common belief that perceptions must enter consciousness to affect our behavior; it shows that our behavior can be guided by sensory information of which we have no conscious awareness. It may be thought of as a converse of the form of anosognosia known as Anton–Babinski syndrome, in which there is full cortical blindness along with the confabulation of visual experience.

We owe much of our current understanding of blindsight to early experiments on monkeys. One monkey in particular, Helen, could be considered the "star monkey in visual research" because she was the original blindsight subject. Helen was a macaque monkey that had been decorticated; specifically, her primary visual cortex (V1) was completely removed. This procedure had the expected results that Helen became blind as indicated by the typical test results for blindness. Nevertheless, under certain specific situations, Helen exhibited sighted behavior. Her pupils would dilate and she would blink at stimuli that threatened her eyes. Furthermore, under certain experimental conditions, she could detect a variety of visual stimuli, such as the presence and location of objects, as well as shape, pattern, orientation, motion, and color. In many cases she was able to navigate her environment and interact with objects as if she were sighted.

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