31 March, 2011
In this issue
How blind peoples' brains adapt to assistive technology
If you observe an experienced user of a screen reading program, such as JAWS or NVDA, when browsing the web, you will be amazed at their level of skill at using assistive technology. New research recently reviewed in the Scientific American has demonstrated that the skill and precision at which these users are able to understand voice synthesis (computerized speech) may be related to the way in which their brains have developed and learnt to adapt to their disabilities.
A large amount of the brain is devoted to processing visual stimuli. For many blind people, the area of the brain known as V1, which responds to light, cannot be utilized as it does not receive the environmental input it requires to develop appropriately. Functional brain imaging, or MRI, has demonstrated that some people who are vision impaired are using this area of the brain in a different way and for a different purpose than sighted individuals. Given that they are more reliant on listening to speech to understand their environment than vision, this area of the brain has been found to adapt and process speech and language instead of visual input, in order to be more functionally useful.
The ability of the brain to adapt in response to its environmental needs has resulted in some vision impaired individuals being able to process speech at a much higher rate than sighted individuals. Whereas sighted people can comprehend speech at a rate of 10 syllables per second, some visually impaired people can comprehend up to 25 syllables per second.
Sean Randall, an experienced screen reader user, has noticed a dramatic improvement in his comprehension over time, "I recently re-read Harry Potter and the Philosopher's stone. I first heard it in audio form 11 years ago and the reading took eight and a half hours. My latest reading, at a comfortable, if leisurely synthetic pace, took precisely one-hundred and fourteen minutes and six seconds."
Like many screen reader users, Sean prefers speech synthesis that sounds clear at high speed, rather than more naturally sounding verbal output from his computer. "I don't want a computer that sounds like a Human", he explains, "I've not yet met a Human who can impart information to me at over 400 words per minute, be it fiction or source code, with the same level of efficacy."
Sean cautions against speaking quickly to people with vision impairments, "I can't process people who yammer at me at high speed; it seems a skill limited to synthetic speech."
The findings pose some interesting questions for Bionic Vision Australia (BVA), an Australian consortium of researchers who are in the process of creating a neurostimulator, or 'bionic eye', to aid vision. Until clinical trials commence, researchers won't really know how the brain will respond to the visual information a bionic eye could deliver. As a result it is hard to know how much 'rewiring' of the brain will be 'un-wired' and how this will affect patients ability to process audio from screen readers and other assistive technologies.
Rewiring of the brain is more pronounced in people who lose their sight at a young age, but the conditions that the bionic eye targets, namely retinitis pigmentosa and age-related macular degeneration, are degenerative conditions, meaning that people lose their sight gradually over time. This means that bionic eye patients would generally be adults who have had well-developed vision in the past, thus the extent to which their brain would be rewired would be less.
"After a patient gets their first implant, there would be a fairly long period of adjustment and training to help the brain make sense of the information it is receiving from the bionic eye", explains Veronika Gouskova from BVA, "The potential psychological implications can also be quite serious. If a person has adapted to having no vision at all, the brain can become overwhelmed with the information it is suddenly flooded with."
"Our first patients will be very carefully selected and clinicians will work very closely with their families and support networks to make sure the adaptation process is as smooth as possible. But until we start working with our first patients, we really can't say what they'll experience and how this will affect them. It is also likely that the responses will vary from patient to patient, while the technology is still quite new."
Patient tests amongst BVA's international colleagues in Germany and the USA have indicated that some people respond very well to having their sight restored, but this research is still in its early stages.
Thank-you to Dr Renee Testa and Veronika Gouskova for their assistance with this article.
Stat of the week
Speed of Completion by Activity (words per minute)
13 Morse code
22 Handwriting - copying text
31 Handwriting - memorized text
180 Screen text
200 Printed text
100 Speech recognition software
150 Audio book
180 Ordinary speech
300 Screen reader
*Note: estimates on speed vary considerably, so please treat these as indicative only.
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