Synesthesia

Know someone who see colors associated with words, letters, and numbers? Maybe for them, the letter “c” is blue, or word “book” is red. They have normal vision, but for them words have distinct colors. They have a rare condition called synesthesia, as reported here.

How do we know it’s for real? Here’s a pretty convincing test, from the same report:

A standard test where color confers a real advantage is a search test where the target is a different color than the distracters surrounding it. Subjects report that the colored target “pops out” of the page. As a result, the time it takes them to pick out the target is about same regardless of the number of distracters in the scene. WO sees “2” as orange and “5” as green but he sees both “6” and “8” as nearly the same shade of dark blue. Using a special font so that the “2” and “5” are mirror images, the researchers made up two sets of computer displays. One set had single white “2s” hidden among varying numbers of white “5s.” The other set had single white “8” hidden among varying numbers of white “6s.”

Non-synesthetes who took these tests found the 2-among-5 search slightly harder than the 8-among-6 search. But WO found the 2-among-5 search much easier and was able to find the target significantly faster than non-synesthetes because the figures appeared as different colors, while his performance on the 8-among-6 search, which look the same to him, was comparable to that of the non-synesthetes.