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 are blind 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 blindside often in a forced-response or guessing situation, even though they cannot actually see the stimulus. Research shows a surprising amount of accuracy in the guesses of blind patients. 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 is known as Type 1 blindsight. Type 2 blindsight occurs when patients claim to have a feeling that there has been a change within their blind area, for example, movement, but that it was not a visual percept. This phenomenon challenges what we once believed to be true, that perceptions must enter consciousness to affect our behavior. Blindsight proves that our behavior can be guided by sensory information of which we are completely unaware. (Carlson, 2010) 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.

There are two types of blindsight. In Type 1, subjects have absolutely no awareness of any stimuli, but, if forced to “guess”, can predict (at levels significantly above chance) aspects of a visual stimulus, such as location or type of movement. In Type 2 blindsight, subjects have some awareness, for example, of movement within the blind area, but no visual percept.