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Illustration demonstrates the concept
of visual-to-auditory sensory substitution. Images from a camera are
converted into “soundscapes,” using a predictable algorithm,
allowing the user wearing earphones to listen to and then interpret
the visual information coming from the camera. This enables blind
people to decode the visual information within the sounds and
perceive complex images of people, words and objects.
Credit: Illustration by Karin
Kedar and Michael Gluhoded
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Jerusalem – Common wisdom has it that
if the visual cortex in the brain is deprived of visual information
in early infanthood, it may never develop properly its functional
specialization, making sight restoration later in life almost
impossible.
Scientists at the Hebrew University of
Jerusalem and in France have now shown that blind people – using
specialized photographic and sound equipment – can actually "see"
and describe objects and even identify letters and words.
The new study by a team of researchers,
led by 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 Ph.D. candidate Ella Striem-Amit, has
demonstrated how this achievement is possible through the use of a
unique training paradigm, using sensory substitution devices (SSDs).
SSDs are non-invasive sensory aids that
provide visual information to the blind via their existing senses.
For example, using a visual-to-auditory SSD in a clinical or everyday
setting, users wear a miniature camera connected to a small computer
(or smart phone) and stereo headphones.
The images are converted into
"soundscapes," using a predictable algorithm, allowing the
user to listen to and then interpret the visual information coming
from the camera. The blind participants using this device reach a
level of visual acuity technically surpassing the world-agreed
criterion of the World Health Organization (WHO) for blindness, as
published in a previous study by the same group.
The resulting sight, though not
conventional in that it does not involve activation of the
ophthalmological system of the body, is no less visual in the sense
that it actually activates the visual identification network in the
brain.
The study shows that following a
dedicated (but relatively brief) 70 hours of unique training paradigm
developed in the Amedi lab, the blind people could easily use SSDs to
characterize images into object categories, such as images of faces,
houses, body shapes, everyday objects and textures. They could also
identify even more complex everyday objects -- locating people's
positions, identifying facial expressions, and even reading letters
and words (for demos, movies and further
information: http://brain.huji.ac.il/).
These unprecedented behavioral results
are reported in the current issue of the prestigious neuroscience
journal, Neuron.
The Hebrew University study went on
further to actually test what happens in the brain when the blind
learn to see with sounds. Specifically, the group 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.
Prof. Amedi, and Ella Striem-Amit used
functional magnetic resonance imaging (fMRI) to measure the neural
activity of people blind from birth as they "saw" -- using
the SSD -- high-resolution images of letters, faces, houses, everyday
objects and body-shapes. Surprisingly, not only was their visual
cortex activated by the sounds, their brain showed selectivity for
visual categories which characterize the normally developing, sighted
brain.
A specific part of the brain, known as
the Visual Word Form Area, or VWFA -- that was first discovered in
sighted people by Profs. Laurent Cohen and Stanislas Dehaene of
Pitie-Salpétriere Hospital-INSERM-CEA, of France, co-authors of the
current article -- is normally very selective.
In sighted people, it has a role in
reading, and is activated by seeing and reading letters more than by
any other visual object category. Astonishingly, the same was found
in this area in people deprived of sight. Their VWFA, after only tens
of hours of training in SSD use, showed more activation for letters
than for any of the other visual categories tested.
In fact, the VWFA was so plastic to
change, that it showed increased activation for SSD letters after
less than two hours of training by one of the study participants.
"The adult brain is more flexible
that we thought," says Prof. Amedi. In fact, this and other
recent research from various groups have demonstrated that multiple
brain areas are not specific to their input sense (vision, audition
or touch), but rather to the task, or computation they perform, which
may be computed with various modalities. (This information was
summarized in a recent review by the Amedi research group published
in the journal Current Directions in Neurology.)
All of this suggests that in the blind,
brain areas might potentially be "awakened" to processing
visual properties and tasks even after years or maybe even lifelong
blindness, if the proper technologies and training approaches are
used, says Amedi.
The findings also give hope that
reintroduced input into the visual centers of the blind 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"
says Prof. Amedi.
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I do not know how this technology really worked. But I hope this research comes up with some new results..
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