turning points The blind leading the sighted An eye-opening experience of the wonders of .

Richard Gregory ne of the most dramatic, though very rare, human experiences is the Oacquisition of sight as an adult following blindness from birth. This hap- pened to Sidney Bradford at the age of 52, having been recorded as blind at ten months and almost certainly blind, owing to an infection, from birth. Studying Bradford’s new vision, and how it developed over the few years remaining to him, was the turning point at least for my appreciation of the wonders of perception. It was my research assistant,Jean Wallace, who saw in a local paper in 1959 that a man, blind from birth and now 52, was about to receive new eyes — or rather, corneal grafts Common : a formerly blind patient was able to transfer knowledge from touch to his new sight. that might allow him to see. We gathered every visual trick and gadget we thought blind,and now adult,and taught by his touch appearance. Pictures looked flat and mean- might be relevant from the practical class we to distinguish between a cube and a sphere… ingless. Perspective meant nothing to his ran in the Cambridge Psychological Labora- [Then suppose] the blind man be made to visual system,yet he could judge the distances tory. Dropping teaching and other commit- see: query, whether by his sight, before he and sizes of objects that were already familiar ments, we drove to a Midlands hospital in touched them, could he distinguish and tell from touch, such as chairs scattered around time to see Bradford just after his first eye was which was the globe and which the sphere? To the ward — although he was wildly wrong opened to the light. which the acute and judicious proposer about distances to the ground from the hos- We found a cheerful, confident, middle- answers, ‘Not. For, though he has obtained pital windows. Evidently, earlier touch expe- aged man who was willing to be investigated the experience of how a globe, how a cube, rience and behaviour such as walking, cali- and, so far as we could tell then or later, was affects his touch, yet he has not yet obtained brated and gave to his vision,which was truthful and honest.But an initial shock near- the experience, that what affects his touch so almost useless for untouchable objects or pic- ly made us turn back with the disappoint- or so, must affect his sight so or so.’” The tures. His unusual responses to the figures ment that this must be a put-up job,or at least philosopher George Berkeley (1685–1753) suggested that many illusions result from a Great Mistake: he correctly read the time on held the same opinion.And so,essentially,did cognitive processing, rather than physiologi- the clock in the ward. Could he have guessed psychologists at the time Bradford gained his cal signal processing occurring early in the it? Borrowing a nurse’s alarm clock, we set its vision, notably Donald Hebb. This distin- visual system; this led to experiments and hands to various positions,and he told us the guished Canadian psychologist, author of interesting controversies that persist today. times it showed. Taking a large watch, which The Organization ofBehaviour(1949),coined Vision was generally thought to be sepa- had no glass,from the top pocket of his jacket, the idea of neural nets and believed sight to be rate from the other senses, and is still mainly he told its time by rapidly touching its hands, a skill acquired only gradually. studied in isolation; yet Bradford showed as he had done for many years.So he could see Early cases of operable blindness that exploratory touch — as well no doubt as immediately, from earlier touch experience. (reviewed by Marius von Senden in 1932) taste, sound and other sensory experiences At least for us, this was a turning point for involved lens cataracts, sight being given by — gives richness and meaning to retinal understanding vision. removal of the lens. But as these primitive images. For optical images are but ghosts, Also rather by accident, we found he could operations did not allow a decent retinal materialized into objects by perceptual expe- read the name of the popular Everybody’s mag- image for weeks or months, patients’ slow- rience of the non-visual properties of things. azine,guessing the title from its upper-case let- ness to see was interpreted as evidence that Now there is a new case. Mike May, in ters even though he could not read the lower- they had no initial vision. It is now known California, lost sight in both eyes from a case ones.It turned out that at the blind school that babies a few hours beyond birth take chemical accident when he was three-and- he had attended, the boys were taught to read interest in faces. Their responses to stimuli a-half years old. He regained sight by a upper-case letters by touch, from wooden important to survival, such as facial expres- corneal graft, but the unique operation blocks engraved for the purpose. Technically, sions, suggest considerable immediate required the use of stem cells, which is why Bradford showed cross-modal transfer from vision, as Bradford had. But Hebb was right this was delayed until 2000, when he was in touch to vision, which no one knew about at that visual learning is important and slow — his early forties[ok?].May’s first visual expe- that time, although it was soon discovered by it was only knowledge acquired from touch riences,and his currently developing vision, other researchers studying primates. that enabled Bradford to interpret an artifi- mirror those of Bradford’s late entry to the The classical reference for considering the cial stimulus,such as a clock face,correctly. world of sight.And what is happening in his possibilities of adult sight given infant blind- Bradford’s responses to well-known illu- brain can now be investigated, thanks to ness is John Locke’s An Essay Concerning sion figures were far from normal. He per- another miraculous turning point: the Human Understanding (1690). Locke quotes ceived far less distortion,and he did not expe- advent of brain imaging technologies. a letter from his friend William Molyneux, rience the flipping ambiguity of the Necker Richard Gregory is at the Department of posing the question: “Suppose a man born Cube, or other such dynamic changes of Experimental , University of , UK.

NATURE | VOL 430 | XX AUGUST 2004 | www.nature.com/nature 1