We often talk about which sense we would choose to lose, if we had to give one up. But sometimes, the borderline between senses is not so clear. Dr. Sacks explored this theme in Seeing Voices, and he will return to it in his forthcoming book, The Mind’s Eye.
There is, of course, a “consensus” of the senses—objects are heard, seen, felt, smelt, all at once, simultaneously; their sound, sight, smell, feel all go together. This correspondence is established by experience and association. This is not, normally, something we are conscious of, although we would be very startled if something didn’t sound like it looked—if one of our senses gave a discrepant impression. But we may be made conscious, very suddenly and startlingly, of the senses’ correspondence, if we are suddenly deprived of a sense, or gain one. Thus David Wright “heard” speech, the moment he was deafened; an anosmic patient of mine “smelt” flowers, whenever he saw them (Sacks, 1985); and a patient described by Richard Gregory (in “Recovery from early blindness: a case study,” reprinted in Gregory, 1974) could at once read the time on a clock when he was given his sight (he had been blind from birth) by an eye operation: before that he had been used to feeling the hands of a watch with its watch-glass removed, but could make an instant “transmodal” transfer of this knowledge from the tactile to the visual, as soon as he was able to see.
From Seeing Voices, Vintage paperback edition, p. 133.