Blindsight is when a person who cannot see consciously responds to visual stimuli due to damage in the occipital lobe. There are two types of blindsight, with individuals able to describe aspects of visual stimuli with great accuracy. Blindsight reveals a distinction between conscious and unconscious mental processes and can occur in people with scotomas.
Blindsight is a rare occurrence in which a perceptually blind individual, i.e. one who cannot see consciously, is still able to respond to some form of visual stimuli. This unusual phenomenon is usually the result of damage to the occipital lobe, the part of the brain responsible for vision. The eyes still function normally, but the part of the brain that translates visual stimuli into understandable sensory data is inoperable. An individual who has blindsight is essentially blind, as he cannot read, distinguish colors or see anything in the normal sense. Tests reveal that they are, however, able to describe various characteristics of a given visual stimulus with an accuracy that cannot be explained by pure chance.
There are two main types of blindsight that scientists have observed and classified. People with blindsight of the first type are completely unaware of any visual stimuli. When pressed, however, they can describe aspects of visual stimuli such as movement and location with great accuracy. Individuals with type two blindsight possess an indirect awareness of the presence of visual stimuli and may or may not be able to describe the location of an object. They may, for example, be aware of their eyes moving to track a moving object even though they cannot actually see the object.
The study of blindsight has revealed an interesting distinction between action and awareness of action. An individual may possess the ability to see but be completely unaware of this ability. This also suggests a stark difference between conscious and unconscious mental processes. A blind individual cannot consciously track an object as it moves across his field of vision. The fact that some blindsighted individuals are, in fact, able to follow movement with their eyes clearly demonstrates some level of unconscious processing.
This phenomenon has also been demonstrated in people who do not suffer from complete blindness on several occasions. Damage to the primary visual cortex can cause scotomas, or “islands” of blindness, in an otherwise completely normal field of vision. Just as in completely blind people, people with scotomas are sometimes able to predict the presence of visual stimuli with significant accuracy or are able to follow a moving stimulus with their eyes. This is also referred to as blindsight, even though the individual may not be completely blind. The eyes are still functioning properly and visual data is present, but the mechanisms by which that information can be transformed into intelligible sensory data are non-functional.
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