[WATCH VIDEO: Examples of Visual Stimuli Used in SSD Training]
Lawrence LeBlond for redOrbit.com – Your Universe Online
It has been long believed that blindness in early infanthood makes sight restoration later in life next to impossible as the brain´s visual cortex has been deprived of visual information. But some researchers have shown that blind people, even those with lifelong blindness, can learn to process visual input using sound.
Working from the Hebrew University of Jerusalem, researchers, with the use of specialized photographic and sound equipment, demonstrated that blind people can actually “see” and describe objects and even identify letters and words.
Publishing their work in the November issue of the journal Neuron, study leader 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 and PhD candidate Ella Striem-Amit, said this work challenges long-held beliefs that people with lifelong blindness cannot visualize objects in their mind.
“The adult brain is more flexible that we thought,” Amedi noted in a press release.
For their study, Amedi and colleagues used sensory substitution devices (SSDs), non-invasive sensory aids that provide visual information to the blind via existing senses. Using a visual-to-auditory SSD allows a user to listen to and interpret visual information coming from this small camera that is connected to a small computer and stereo headphones. Images are converted into “soundscapes” using a predictable algorithm.
The participants using this device can reach a level of visual acuity technically surpassing the criterion for blindness set by the World Health Organization; This criterion came from the results of a previous study conducted by the same group of researchers.
The visual acuity attained via these SSDs is unique in the fact that rather than activating the ophthalmological system to garner visualizations, the devices actually activate the visual identification network of the brain.
Amedi showed that with a relatively brief 70 hours of unique training, blind people could easily use SSDs to characterize images into object categories, such as images of faces, body shapes, buildings and textures. They were also able to complete complex tasks, such as locating people´s positions, identifying facial expressions, and reading letters and words.
The researchers also studied what happens in the brain when these blind test subjects learn to see with sounds. Specifically, the researchers tested the ability of this high-acuity vision to activate the supposedly dormant visual cortex of the blind, even though it was taught to process the visual images through sounds only in adulthood.
Coauthors of the current research, Professors Laurent Cohen and Stanislas Dehaene of Pitie-SalpÃ©triere Hospital-INSERM-CEA, of France, first discovered a specific brain area, known as the Visual Word Form Area (VWFA), in a previous study.
In sighted people this region is very selective, as it plays a role in reading and is activated by seeing and reading letters more than any other visual object category.
To the amazement of the researchers, the same was found in this brain region in people deprived of sight. The VWFA in blind people showed more activation for letters than any other visual category tested after only 10 hours of training, and showed increased activation for SSD letters after only two hours of training in one test subject.
These findings suggest that in the blind, brain areas might potentially be “awakened” to allow visual processing after years, if not a lifetime, of blindness, said Amedi, adding that the findings give hope that introduced input into the visual centers of the brain could potentially restore 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 such as bionic eyes” he concluded.