Using a brain-computer interface, a clinical trial participant who lost the ability to
speak was able to create text on a computer at rates that approach the speed of regular
speech just by thinking of saying the words.
Scientists with the BrainGate research collaborative have reached a major milestone in restoring
speech for people who have lost the ability to speak due to paralysis.
In a new study published in Nature, the researchers describe using sensors implanted in areas
of the cerebral cortex associated with speech to accurately turn the brain activity of a
patient with ALS who lost the ability to speak into words on a screen just by the patient
thinking of saying them.
The clinical trial participant — who can no longer use the muscles of her lips, tongue,
larynx and jaws to enunciate units of sound clearly — was able to generate 62 words
per minute on a computer screen simply by attempting to speak.
This is more than three times as fast as the previous record for assisted communication
using implanted brain-computer interfaces (BCIs) and begins to approach the roughly
160-word-per-minute rate of natural conversation among English speakers.
The study shows that it’s possible to use neural activity to decode attempted speaking
movements with better speed and a larger vocabulary than what was previously possible.
The study is the latest in a series of advances in brain-computer interfaces made by the BrainGate
consortium, which along with other work using BCIs has been developing systems that enable
people to generate text through direct brain control for several years.
Previous incarnations have involved trial participants thinking about the motions involved
in pointing to and clicking letters on a virtual keyboard, and, in 2021, converting a paralyzed
person’s imagined handwriting onto text on a screen, attaining a speed of 18 words
per minute.
The researcher says that with credit and thanks to the extraordinary people with tetraplegia
who enroll in the BrainGate clinical trials and other BCI research, they continue to see
the incredible potential of implanted brain-computer interfaces to restore communication and mobility.
One of those extraordinary people is Pat Bennett, who having learned about the 2021 work, volunteered
for the BrainGate clinical trial that year.
Bennett, now 68, is a former human resources director and daily jogger who was diagnosed
with ALS (amyotrophic lateral sclerosis) in 2012.
For Bennett, the progressive neurodegenerative disease stole her ability to speak intelligibly.
While Bennett’s brain can still formulate directions for generating units of sound called
phonemes, her muscles can’t carry out the commands.
As part of the clinical trial, neurosurgeon placed two pairs of tiny electrodes about
the size of a baby aspirin in two separate speech-related regions of Bennett’s cerebral
cortex.
An artificial-intelligence algorithm receives and decodes electronic information emanating
from Bennett’s brain, eventually teaching itself to distinguish the distinct brain activity
associated with her attempts to formulate each of the phonemes — such as sh sound
— that are the building blocks of speech and compose spoken English.
The decoder then feeds its best guess concerning the sequence of Bennett’s attempted phonemes
into a language model, which acts essentially as a sophisticated autocorrect system.
This system then converts the streams of phonemes into the sequence of words they represent,
which are then displayed on the computer screen.
To teach the algorithm to recognize which brain-activity patterns were associated with
which phonemes, Bennett engaged in about 25 training sessions, each lasting about four
hours, where she attempted to repeat sentences chosen randomly from a large data set.
As part of these sessions, the research team also analyzed the system’s accuracy.
They found that when the sentences and the word-assembling language model were restricted
to a 50-word vocabulary, the translation system’s error rate was 9.1%.
When vocabulary was expanded to 125,000 words, large enough to compose almost anything someone
would want to say, the error rate rose to 23.8%.
The researchers say the figures are far from perfect but represent a giant step forward
from prior results using BCIs.
They are hopeful of what the system could one day achieve — as is Bennett.
For those who are nonverbal, this means they can stay connected to the bigger world, perhaps
continue to work, maintain friends and family relationships.
Imagine how different conducting everyday activities like shopping, attending appointments,
ordering food, going into a bank, talking on a phone, expressing love or appreciation
— even arguing — will be when nonverbal people can communicate their thoughts in real
time.