London, Sept 15 : Deaf people can sense their muscle movements to speak correctly, which makes them retain their speech years after they have lost their hearing abilities, according to a new research.
Neuroscientist David Ostry and his colleague Sazzad Nasir at McGill University in Montreal, Canada, say that people could sense when they speak incorrectly, the same way we can sense wrong speech when contorting our mouth like Elvis.
During a study, the researcher asked five deaf volunteers to talk while a robot nudged their jaws slightly, and all the participants easily learnt to compensate for the perturbation.
"One of the real mysteries of human language is that people who become deaf as adults remain capable of producing intelligible speech for years in the complete absence of any auditory input," New Scientist quoted Ostry as saying.
Most neuroscientists studying speech focus on how the brain learns from sounds to correct for errors.
However, Ostry said that just like tennis players learn whether a forehand shot will land in or out just from the feel, people can sense whether or not they are speaking correctly.
In order to separate the ability of learning by hearing, the researchers enlisted the help of five deaf people with cochlear implants that allowed them to hear.
The participants were asked to repeat short words such as "sass" and "sane" that flashed onto a computer screen, while their implants were switched off. A robot arm pushed gently on their jaw simultaneously, moving it a few millimetres.
The robot could also measure how much a subject pushed back. According to Ostry, the nudge was quite gentle to affect speech.
"Subjects will leave the lab and often there's no conscious awareness that the robot was doing anything," he said.
After going through hundreds of words, the participants corrected for the prodding by moving their jaws several millimetres to resist the robot's nudge. The researchers were surprised to see that all the subjects made the same adjustment when their cochlear implants were turned back on.
"When you talk you want to get movement right perhaps as much as you want the speech to sound properly. It's not only making it sound right, it's making it feel right," said Ostry.
He further added that harnessing this sixth sense for speech may improve the speech for people with stutters and other speech problems.
"It's worth investing in therapies for speech that focus on movements and possibly focus on movement independent of speech sounds," he said.