D.B. (blindsight patient)
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Blindsight overview
Blindsight is the condition in which a person is able to respond to a visual stimulus without consciously perceiving it. The visual cortex, also called V1 or the striate cortex, receives input from the retina which makes visual discrimination possible. When V1 is removed, however, it is sometimes still possible to make "visual" discriminations because the input from the retina travels through other areas in the brain, which may also be the reason this phenomenon occurs. [1]
Origin of D.B.'s blindsight
D.B. is the first and most intensively studied case of blindsight. D.B.'s blindsight was caused not by brain damage but by the removal of a non-malignant tumor from his right visual cortex at the age of 26 which subsequently left him unable to detect things in his left visual field. Although an MRI wasn't possible because of the metal clips left in D.B.'s head after surgery, psychologists were able to use a CT scan to get a better look at the legion when D.B. was studied again in 2007.[2]
Weisenkrantz and Warrington study
Psychologists L. Weisenkrantz and Elizabeth Warrington first began studying D.B. in 1973 at the National Hospital in London. D.B. was tested with a "monkey-type" in which he was given no prompting for what he was looking for and was simply asked to reach out and touch the stimuli or to "guess" about what was being presented to him.
D.B. responded by successfully making "guesses" about things that he said he couldn't see. He was able to tell which direction grating was set and whether an object was moving or not. He could also reach for objects without consciously being aware of their presence. In fact, a great deal of the tests he participated in were all about guesswork, rather than conscious though, in D.B.'s mind and he was shocked when he was shown how accurate he had been across the board. [3]
After Weisenkrantz and Warrington published a book about their work with D.B. and blindsight in 1986, the two worked with D.B. again in 2007 and noted that his sensitivity had increased considerably. He was able to distinguish the expressions on faces presented to him as well as suddenly being able to see after-images of unconsciously perceived stimuli, which the researchers dubbed "prime sight." D.B. could accurately predict grating, as before, but he could also distinguish nearly perfectly whether he was being shown a square or a circle.[4]
Later research also allowed for the analysis of pupil dilation both in D.B. and in another blindsight patient who had been studied in the intermediary period. The pupils in both patients tended to constrict similarly when they were presented with certain visual stimuli, implying that this method could possibly be used in the future to help diagnose the occurrence of blindsight.[5]
