Vision seekers: giving eyesight to the blind raises questions about how people see

Science News, Nov 22, 2003 by Bruce Bower

Objects and faces also puzzle May. He has difficulty identifying everyday items, distinguishing male from female faces, and recognizing emotional expressions on unfamiliar faces. May keeps track of people's faces by noting hair length, eyebrow shape, and other individual features.

May does track his own and others' movements with precision. He also distinguishes shaded areas from illuminated surfaces. With these capabilities, he's made a transition from being an expert blind skier, who depended on verbal directions from a sighted guide, to being a competent sighted skier.

May's chipper outlook and visual accomplishments so far are inspiring, remarks psychologist Richard L. Gregory of the University of Bristol in England. Says Gregory: "It is possible to live happily with delayed sight and to gain from the new experiences"

BLIND BRAINS The transition from prolonged blindness to sudden sight doesn't demand just psychological resilience. It requires unprecedented accommodations from the brain.

Brain--imaging studies indicate that neural areas devoted to vision, which comprise as much as one-quarter of the brain in primates, take on entirely different responsibilities in blind individuals. For instance, vision--associated regions of the brain appear to facilitate the sensitivity of touch among those without sight. In 1996, researchers reported that the visual cortex at the back of the brain showed increased activity when blind people use the tips of their fingers to read Braille publications.

Moreover, psychological investigations suggest that blind people perform better than their sighted peers do on tests of verbal memory. Parts of the brain's visual system--including tissue that otherwise serves as an entry point for visual information from the eyes--become more active when blind participants recall previously studied words and generate verbs for a list of braille nouns, according to a report in the July Nature Neuroscience.

Blind volunteers with the strongest verbal memories displayed especially intense activity in these brain areas when they performed the word tasks. In sighted volunteers, these neural tissues remained calm during the same verbal tests, say neuroscientist Ehud Zohary of Hebrew University in Jerusalem and his colleagues. In sighted people, language--related brain areas far removed from the visual cortex handle verbal memory.

Studies such as Zohary's suggest that the brain undergoes a major reorganization in people who are blind from birth to adulthood, enabling tissue that would otherwise deal in vision to take on other sensory duties, as well as language and memory assignments.

If so, the brains of formerly blind children should yield scientific surprises. Sinha's 10-year-old cataract patient in India undoubtedly relishes the possibility of mustering a few neural revelations. In this boy's case, eyesight may spark insight.