Scientists have taken the first step toward making it possible to eavesdrop on people's thoughts by successfully decoding brain waves associated with hearing.
Their eventual goal is to create a prosthetic device that would provide a voice for those who are unable to speak.
A variety of health conditions can rob people of their ability to speak, including stroke, a neuromuscular disease called amyotrophic lateral sclerosis or Lou Gehrig’s disease, and locked-in syndrome, in which individuals are completely awake and aware of their surroundings but unable to move or communicate with the outside world.
To help these people regain a voice, scientists at the University of California, Berkeley, set out to build a device that could translate human thoughts into speech. They have achieved a first step toward that goal by decoding the electrical activity in a region of the brain, called the superior temporal gyrus, that’s stimulated by hearing.
Senior researcher Robert Knight, who heads U.C. Berkeley's neuroscience center, says the experiments involved a group of epilepsy patients who listened quietly to words that were played to them.
Researcher Brian Pasley created a computer program that can recognize individual words in the brainwave patterns by their rhythm - or the spacing of syllables - and by their audio frequencies - the high and low sounds in the words.
To obtain the sound-stimulated brainwave patterns, Pasley used a device called an electroencephalograph, which measures the electrical firing of the patients’ auditory circuits through electrodes already implanted in the patients' brains when they hear spoken words.
He reproduced those words digitally by feeding the brain wave data into an electronic voice synthesizer.
The next step will be to see whether brainwaves generated not by hearing a word but by just thinking it could also be converted electronically into speech.
“I think there’s some evidence that in certain cases the same brain areas will activate or turn on when you are imagining sounds or speech as to when you are actually listening," Pasley says. "But still, a lot of work needs to be done to really understand how similar those two processes are or how different. We just don’t know at this point.”
Pasley’s mentor, Robert Knight, believes it’s only a matter of time before researchers are able to map the brain circuitry involved in conscious speech. He predicts the first device allowing people to talk with their thoughts - literally, to speak their minds - will become a reality in five years.