Giving eyesight to the blind raises questions about how people see
One witheringly hot day last summer, a 10-year-old boy performed a few miracles at a hospital near Calcutta, India. For openers, he caught a balled-up piece of paper thrown to him. Then, he picked up paper clips and inserted them into a holder through a small opening. Looking determined, the boy proceeded to identify drawings of an elephant and other animals. Finally, he greeted all of his physicians and nurses, referring to each by name.
Not impressed? These accomplishments sure looked miraculous to Pawan Sinha, a neuroscientist at the Massachusetts Institute of Technology (MIT) who was in Calcutta visiting the hospital. Sinha knew that the boy had had severe cataracts in both eyes since birth. He had grown up in a poor family, and the reason for his blindness went undiagnosed until he tripped and broke his leg at age 10. A physician treating the boy's leg instantly noticed the youngster's cataracts and arranged for free surgery.
Five weeks later, the boy–a newcomer to the world of sight–dazzled Sinha with visual feats. It's not yet clear whether a child deprived of sight for many years can learn to see the world with all the subtlety and skill of a person who grew up with normal vision, however. Researchers are just beginning to piece together how the brain responds to blindness early in life and then how it reacts to the sudden unleashing of vision, however years or even decades later.
What's evident, though, is that sight requires far more than simply opening one's eyes and letting reality in. Perception, whether through vision or any other sense, is an acquired taste. People learn to make visual sense of faces and other items of interest, often during infancy and early childhood but sometimes over much longer periods.
A person's view of the world feeds off his or her past experiences with three-dimensional space, the physical details of particular settings, and the predictable shapes and colors of various items, to name a few.
When the loss of sight deprives young eyes of visual experience, other faculties fill the void: Brain regions traditionally thought to handle only vision commit to duties ranging from touch processing to verbal memory.
Sinha now finds himself in a position to explore how kids' brains adapt to years of blindness and then respond to the onset of sight. He and his coworkers are tracking the progress of 20 children in India, ages 6 to 15, who grew up sightless before the surgical removal of their cataracts. "I'm amazed at how much these kids can do based on vision shortly after cataract surgery," the MIT scientist says. "No one knows if the visual modality will reclaim areas in their brains that it lost to other senses due to blindness."
It's particularly gratifying to observe the success of formerly blind children at recognizing the faces of their family members, physicians, and other familiar people, Sinha says. He estimates that cataract-induced blindness affects as many as 100,000 children in India.
The "fairly crummy" level of visual detail available to most of the Indian children after cataract surgery encourages them to concentrate on the geography of entire faces, while ignoring the nuances of eyes, mouths, noses, or hair, Sinha says. These children also often recognize even partial or faded pictures of familiar faces, indicating that the youngsters refer to a mental catalogue of whole faces, Sinha says.
Babies, whose vision is also blurry, may similarly perceive whole faces rather than specific facial features, he theorizes.
Yet such speculation runs smack into scientists' limited knowledge about the nature of face perception in formerly blind children, as well as in infants (SN: 7/7/01, p. 10: Faces of Perception).
At least some data on the subject come from studies of Canadians directed by psychologist Daphne Maurer of McMaster University in Hamilton, Canada. Children subjected to cataract-induced blindness in only the left eye for the first 2 to 6 months of life lose an element crucial for discerning facial configurations, Maurer's team reports in the October Nature Neuroscience. As teenagers and young adults, these individuals find it difficult to detect differences in the spacing of eyes and other facial features from one person to another.
In contrast, people of the same age who had right-eye cataracts for 2 to 6 months after birth can discern the distance between facial features as well as people with no prior vision problems do.
Despite lacking this face-recognition skill, adults who had left-eye cataracts removed during infancy still manage to recognize their friends and family and don't report any problems in telling familiar faces apart.
Individual facial features evidently guide recognition. McMaster psychologist Catherine J. Mondloch and her coworkers found that people deprived of left-eye vision as babies could accurately tell when the researchers had substituted different eyes or mouths on previously seen images of faces or had digitally thinned or fattened the faces.
The results, which so far derive from 10 volunteers born with left-eye cataracts and another 10 born with right-eye cataracts, implicate the brain's right side in expert face processing, Mondloch says. It is only during infancy that visual information entering the left eye goes mainly to the right hemisphere, while the right eye sends most of its visual input to the left hemisphere. Thus, the capacity to notice the spacing of facial features develops only if the right hemisphere receives visual stimulation during that brief period of time. Even then, according to other studies directed by Mondloch, this skill isn't fully developed until about age 18.
For instance, when asked to identify matches between pairs of faces with assorted head angles–posed so that the spacing of facial features appeared to vary–10-year-olds with no prior eye problems performed as poorly as adults with former left-eye cataracts did. Given normal visual development, face processing improves sharply between ages 16 and 18, Mondloch says.
She plans to conduct brain-scan and brain-wave studies of cataract patients to determine their neural responses to faces. The McMaster researchers also want to see whether people who had left-eye cataracts removed can be trained to recognize faces solely on the basis of the spacing of eyes and mouths.
Sinha hopes to direct similar studies of Indian youngsters treated for cataracts. Those children will undoubtedly become visually adept in many ways, but they were blind far too long to become face-processing experts, Mondloch suspects. "It's already too late if you receive cataract surgery 2 months after birth," she says.
Even if improvements in vision are marginal for those children surgically thrust into the sighted world after years of blindness, there's room for optimism regarding their adaptation to whatever sight they acquire.
"The kids I've studied show good emotional adjustment after cataract surgery," Sinha says. "It probably helps that adults don't have a lot of expectations about what these children should be able to do as sighted individuals."
Adults who regain their sight after being blind for all or most of their lives are often not so fortunate. Published reports of such cases, which date to 1,000 years ago, often describe an initial elation at being able to see, followed by emotional turmoil, depression, and even suicide.
In his book An Anthropologist On Mars (1995, Knopf), neurologist Oliver Sacks of Albert Einstein College of Medicine in New York recounts the story of Virgil, a man who saw little until having cataract surgery at age 50. Sacks calls Virgil's behavior after cataract removal that of a "mentally blind" person–someone who sees but can't decipher what's out there.
Virgil's perceptual identity, his sense of himself, was tied to experiences that had nothing to do with sight. He often felt torn between first looking at objects or touching them instead, as he had always done.
When feeling visually overloaded, he would act as if he were still blind.
Often confused, Virgil rapidly sank into depression. About 4 months after his surgery, he died of pneumonia.
Michael G. May has adapted much better to his recovered vision. A stem-cell transplant delivered sight to his right eye in 2001 when he was 43, after 40 years of blindness. Ione Fine of the University of Southern California in Los Angeles and her colleagues describe May's visual progress in the September Nature Neuroscience.
May regards the challenge of learning to see as an exciting new chapter in his life. It helps that he's an outgoing, optimistic person with a supportive spouse, according to Fine.
"Mike certainly sees the world differently than others do," she notes. Two years after his surgery, May still has no intuitive grasp of depth perception. As people walk away from him, he perceives them as literally shrinking in size and has to remind himself that they're farther away than they were before.
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."
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.
If you have a comment on this article that you would like considered for publication in Science News, send it to email@example.com. Please include your name and location.
To subscribe to Science News (print), go to https://www.kable.com/pub/scnw/
To sign up for the free weekly e-LETTER from Science News, go to http://www.sciencenews.org/subscribe_form.asp.
Center for Imaging Neuroscience
Department of Neurology
Department of Psychology
University of California, San Diego
9500 Gilman Drive
La Jolla, CA 92093
Richard L. Gregory
Department of Experimental Psychology
University of Bristol
8 Woodland Road
Clifton, Bristol BS8 1TN
Department of Psychology
1280 Main Street West
Hamilton, ON L8S 4K1
Michael G. May
175 Mason Circle
Concord, CA 94520
Catherine J. Mondloch
Department of Psychology
1280 Main Street West
Hamilton, ON L8S 4K1
2 Horatio Street
New York, NY 10014
Massachusetts Institute of Technology
Brain and Cognitive Sciences
45 Varleton Street
Cambridge, MA 02142
Life Science Institute
Interdisciplinary Center for Neural Computation
Bower, B. 2001. Faces of perception. Science News 160(July 7):10-12. Available at [Go to].