Areas of the brain in blind people can learn to process visual input through the use of sound, even after years or perhaps even lifelong blindness, according to new research reported in the November issue of the Cell Press journal Neuron. The findings challenge the common belief that if the visual cortex of the brain is deprived of information in early life, it may never develop functional specialization.
"The adult brain is more flexible that we thought," says senior author Prof.. Amir Amedi, of the Edmond and Lily Safra Center for Brain Sciences and the Institute for Medical Research Israel-Canada at the Hebrew University Medical School.
In their studies, Prof. Amedi and his colleagues taught congenitally blind adults to use sensory substitution devices (SSDs), which are non-invasive sensory aids that provide visual information to the blind via their existing senses. For example, when a person uses a visual-to-auditory SSD, images from a video camera are converted into "soundscapes" that represent the images, allowing the user to listen to and then interpret the visual information coming from the camera (i.e. "seeing" with sounds).
After being taught how to use the SSDs, blind people could use the devices to learn to read, with sounds representing visual images of letters. This skill involved a region of the brain called the Visual Word Form Area (VWFA), which in sighted people is activated by seeing and reading letters. After only tens of hours of training, blind people's VWFA also showed more activation for letters than for any of the other visual categories tested. The findings suggest that, at least in the blind, the tuning of VWFA to reading does not depend on vision. Instead, the VWFA may be selective to the type of information or computation rather than to the type of sensory input.
Blind people could also use SSDs to recognize soundscapes of visually complex categories such as faces, houses, and body parts. The results suggest that distinguishing meaningful shapes does not require vision, even though the brain activity that's needed to do so takes place in the part of the brain normally associated with vision in sighted individuals.
The findings also give hope that reintroduced input into the visual centers of the blind brain could potentially restore complex vision, and that SSDs might be useful for visual rehabilitation. "SSDs might help blind or visually-impaired individuals learn to process complex images, as done in this study, or they might be used as sensory interpreters that provide high-resolution supportive synchronous input to a visual signal arriving from an external device," says Professor Amedi.