The Tangled Bank

Magic has amazed people for centuries however the age old saying “the hand is quicker than the eye” is slightly flawed. The saying should go “the hand is quicker than “the parietal cortex”. The parietal cortex is a small region of the brain located behind your ear and has to do with concentration. Psychologists at the University College of London found that this particular piece of gray matter holds the key to a phenomenon called “change blindness”. Often people overlook the obvious where their attention is challenged.

If subjects are shown pictures of two faces in quick succession on a computer screen then they are able to notice that the two are different. However, if the person is distracted by a menial task, like counting or even by a flicker on the screen, the subject frequently will not notice the change. Current research suggests that the parietal cortex might be involved in this ruse because functional-imaging studies link this region to visual awareness.

Researchers connected test subjects to a transcranial magnetic stimulator, which focuses a magnetic field on a selected area of the brain, and temporarily disrupts the neural circuitry there. Subjects were given the face test and with the machine turned (focused over the parietal cortex) on they usually failed to notice that the faces were different. Although it may seem surprising that the parietal cortex is involved, since it is not a traditional visual area, the cortex is critical to auditory, tactile awareness as well as visual concentration. This really makes you think about how awareness can be easily interrupted by simply concentrating on something else (like when drivers “zone out”). However this does yield new meaning that “magic occurs not in the magician’s hand but in the mind of the spectator.”