Two for Blindness and Neuroscience
by Maureen Duffy
I first published these "advances in neuroscience" stories last year, but believe they remain equally relevant today. I think you'll agree.
Why Can Some Blind People Process Speech Faster Than Sighted Persons?
In a recent issue of Scientific American, an article by R. Douglas Fields, Ph.D., entitled Why Can Some Blind People Process Speech Far Faster Than Sighted Persons? examines the work of a group of researchers from the Hertie Institute for Clinical Brain Research at the University of Tübingen in Germany who may have discovered (but their results are not definitive) scientific support for the widespread belief that blindness creates a "sharpening" or "heightening" of the remaining senses to "compensate" for lost vision.
(Dr. Fields also wrote Michelangelo's secret message in the Sistine Chapel: A juxtaposition of God and the human brain, one of my favorite articles from the past year. Thank you, Dr. Fields!)
Following is Dr. Fields' summary of this fascinating research, the full version of which is available at the Scientific American website:
Neuroscientists reported in November at the Society for Neuroscience's annual meeting in San Diego that they have found an interesting group of real individuals with demonstrated "quickness" in their mental abilities — blind people. Moreover, functional brain imaging now reveals how they achieve these cerebral feats.
Blind people can easily comprehend speech that is sped up far beyond the maximum rate that sighted people can understand. When we speak rapidly, we are verbalizing at about six syllables per second. That hyperactive radio announcer spewing fine print at the end of a commercial jabbers at ten syllables per second, the absolute limit of comprehension for sighted people. Blind people, however, can comprehend speech sped up to 25 syllables per second. Human beings cannot talk this fast. The scientists had to use a computerized synthesizer to generate speech at this speed.
Ingo Hertrich, Ph.D., Hermann Ackermann, M.D., and Susanne Dietrich, Ph.D. wanted to find out what was going on inside the brains of blind people that gives them this ability to understand speech at ultrafast rates. Examining brain regions activated by blind and sighted people while they listened to ultrafast speech and laid inside a ... brain scanner revealed that in blind people, the part of the cerebral cortex that normally responds to vision was responding to speech.
Dr. Ackermann explained that the age at which a person loses sight is likely to be critical in rewiring brain regions controlling hearing to the region that normally processes vision. In people who are born blind, the visual cortex is completely unresponsive to any auditory or visual stimulation. This region of the brain becomes functionally disconnected because visual input is necessary early in life to wire up visual brain circuitry properly. (All study subjects had lost their sight between two and 15 years of age.)
The full version is available at the Scientific American website.
The Brain May Adapt to Vision Loss by Increasing the Speed of Tactile Perception
From the Society for Neuroscience website:
People who are blind from birth are able to detect tactile information faster than people with normal vision, according to a recent study in The Journal of Neuroscience.
The brain requires a fraction of a second to register a sight, sound, or touch. In this study, a group of researchers led by Daniel Goldreich, Ph.D., of McMaster University explored whether people who have a special reliance on a particular sense — in the way blind people rely on touch — would process that sense faster.
The authors tested the tactile skills of 89 people with sight and 57 people with various levels of vision loss. The volunteers were asked to discern the movements of a small probe that was tapped against the tips of their index fingers. Both groups performed the same on simple tasks, such as distinguishing small taps versus stronger taps.
But when a small tap was followed almost instantly by a larger and longer-lasting vibration, the vibration interfered with most participants' ability to detect the tap — a phenomenon called masking. However, the 22 people who had been blind since birth performed better than both people with vision and people who had become blind later in life.
The authors measured the minimum amount of time needed for participants to perceive sensory input by varying the period between the tap and the vibration. They found that congenitally blind people required shorter periods than anyone else. Those same individuals also read braille fastest.
The findings suggest that early onset blindness leads to faster perception of touch. However, whether that advantage is due to the brain adapting to the absence of vision — a change called plasticity — or to a lifetime of practicing braille is still unclear.
As always, VisionAware will provide updates on this and other brain and neuroscience research as the results become available.
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