Researchers is the US have developed a brain-computer interface (BCI) that has enabled a woman with severe paralysis from a brainstem stroke to speak through a digital avatar.
It is the first time that either speech or facial expressions have been synthesised from brain signals.
The system can also decode these signals into text at nearly 80 words per minute, a significant improvement over commercially available technology.
Edward Chang, MD, chair of neurological surgery at the University of California San Francisco (UCSF), who has worked on the brain computer interface, or BCI, for more than a decade, hopes this latest research breakthrough will lead to an FDA-approved system that enables speech from brain signals in the near future.
Chang said:
“Our goal is to restore a full, embodied way of communicating, which is really the most natural way for us to talk with others,” said Chang, who is a member of the UCSF Weill Institute for Neuroscience and the Jeanne Robertson Distinguished Professor in Psychiatry.
“These advancements bring us much closer to making this a real solution for patients.”
Chang’s team previously demonstrated that it was possible to decode brain signals into text in a man who had also experienced a brainstem stroke many years earlier.
The new study demonstrates something more ambitious: decoding brain signals into the richness of speech, along with the movements that animate a person’s face during conversation.
Chang implanted a paper-thin rectangle of 253 electrodes onto the surface of the woman’s brain over areas that his team has discovered are critical for speech.
The electrodes intercepted the brain signals that, if not for the stroke, would have gone to muscles in her, tongue, jaw and larynx, and her face.
A cable, plugged into a port fixed to the woman’s, connected the electrodes to a bank of computers.
For weeks, the participant worked with the team to train the system’s AI algorithms to recognise her unique brain signals for speech.
This involved repeating different phrases from a 1,024-word conversational vocabulary over and over again, until the computer recognised the brain activity patterns associated with the sounds.
Rather than train the AI to recognise whole words, the researchers created a system that decodes words from phonemes.
These are the sub-units of speech that form spoken words just as letters form written words. “Hello,” for example, contains four phonemes: “HH,” “AH,” “L” and “OW.”
Using this approach, the computer only needed to learn 39 phonemes to decipher any English word.
The approach both enhanced the system’s accuracy and made it three times faster.
Sean Metzger, who developed the text decoder with Alex Silva, both graduate students in the joint Bioengineering Program at UC Berkeley and UCSF, said: “The accuracy, speed and vocabulary are crucial.
“It’s what gives a user the potential, in time, to communicate almost as fast as we do, and to have much more naturalistic and normal conversations.”
To create the voice, the team devised an algorithm for synthesising speech, which they personalised to sound like her voice before the injury, using a recording of her speaking at her wedding.
The researchers animated the avatar with the help of software that simulates and animates muscle movements of the face, developed by Speech Graphics, a company that makes AI-driven facial animation.
The team created customised machine-learning processes that allowed the company’s software to mesh with signals being sent from the woman’s brain as she was trying to speak and convert them into the movements on the avatar’s face.
This makes the jaw open and close, the lips protrude and purse and the tongue go up and down, as well as the facial movements for happiness, sadness and surprise.
Kaylo Littlejohn, a graduate student working with Chang and Gopala Anumanchipalli, PhD, said: “We’re making up for the connections between the brain and vocal tract that have been severed by the stroke.
“When the subject first used this system to speak and move the avatar’s face in tandem, I knew that this was going to be something that would have a real impact.”
An important next step for the researchers is to create a wireless version that would not require the user to be physically connected to the BCI.
Co-first author David Moses, PhD, an adjunct professor in neurological surgery, said:
“Giving people the ability to freely control their own computers and phones with this technology would have profound effects on their independence and social interactions.”
