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How we change what others think, feel, believe and do
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How we change what others think, feel, believe and do |
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Blindsight
Explanations > Brain stuff > Blindsight Description | Discussion | See also
DescriptionA person with blindsight may, on the surface, be completely or partially blind. When presented with an object in a zone where they cannot consciously see, they will honestly declare that they cannot see it. Yet if they are asked to guess things about the object or point to it, they are able to perform such tasks with accuracy somewhat above chance. When asked about how they did this, they typically rationalize the success as luck. In Type 1 blindsight, the person is not aware of any stimuli, but can predict quite well aspects such as location or movement of a stimulus. Type 2 blindsight is where the person has some awareness but no visual perception, for example their eyes may follow an object but they cannot point to it. DiscussionThe brain processes vision in more than one place. In particular, it is processed both in the mammalian cortex (significantly in an area called V1) and also in the primitive mid-brain, where basic functions such as eye movement are managed. Cortical visual processing is more complex, of course; the primitive systems allow for identifying basic objects and movement. Thus if the V1 area is damaged, the mid-brain can still perceive visual signals, which can then subconsciously alert the cortex. A significant point about this is that consciousness does not exist in all parts of the brain. Blindsight was first identified by Pöppel, Held and Frost in 1973. This was followed by a a deep study of a patient known as 'DB'. See alsoPöppel, E., Held, R., and Frost, D. (1974). Residual visual function after brain wounds involving the central visual pathways in man. Nature, 243, 295-296. Weiskrantz, L. (1986, 1998). A Case Study and Implications. Oxford: Oxford University Press. |
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