Settling a decades-old debate, scientists have confirmed that blind people are just as adept at tracking sounds as people with normal vision. The finding, reported in this week's Nature, could lead to new devices for helping blind people navigate their environments.
Some scientists have argued that vision is essential for locating sounds. They point to studies showing that when an owl's vision is distorted with spectacles, the bird has trouble finding the sources of sounds. But others have argued that blind people can mentally map sounds perfectly well, because their brain compensates for a lack of vision by rewiring the visual cortex to help interpret sounds.
To test these theories, physiologist Franco Lepore at the University of Montreal and his colleagues asked three groups of subjects--eight totally blind people, three with residual peripheral vision, and 29 sighted people--to point to the source of a series of noises played through an array of 16 hidden loudspeakers, arranged in a semicircle. Sighted and completely blind subjects located the sounds equally well. But the partially blind were much less accurate, especially with sounds almost directly ahead. This finding was surprising, the researchers say. They had predicted that people with some peripheral vision would at least do as well identifying the source of peripheral sounds as those with normal vision.
Lepore's group suggests that the brain of a blind person may form new connections with nerves in the visual cortex, allowing them to interpret sounds. In those with partial sight, visual and auditory signals would compete, preventing a complete re-wiring. The partial visual input might simply confuse the sound-mapping process.
"I think it's really a landmark paper," says Josef Rauschecker, a neuroscientist at Georgetown University in Washington, D.C., because it confirms the ability of blind people to use sound for orientation. Rauschecker says the finding could spark research on equipment that helps blind people use sounds to "see" their environment, such as speakers that would bounce sound off of nearby objects, giving the blind a clearer sound picture of their surroundings.