Scientists have developed a brain implant that can read people's thoughts and express their thoughts.
The San Francisco University of California team says the technology is "intoxicating."
They add that their findings, published in the journal Nature, could help people if they are deprived of their ability to speak.
Experts said the results were convincing and hoped to restore the language.
How does it work?
The mind reading technology works in two stages.
First, an electrode is implanted in the brain to pick up the electrical signals that move the lips, tongue, voice box and jaw.
Then powerful computing simulates how the mouth and throat movements make different sounds.
This leads to synthesized speech originating from a "virtual vocal tract".
Why does it do it?
One would think it would be easier to search the brain for the pattern of electrical signals that code for each word.
Attempts to do so, however, have had limited success.
Instead, it focused on the shape of the mouth and the sounds that allowed the scientists to achieve a world first.
- The deeply deaf girl who found her voice after a brain operation
- Patients with screaming are supported in the Parkinson's Course
Professor Edward Chang, one of the researchers, said, "For the first time, this study shows that we can generate whole spoken sentences based on a person's brain activity.
"This is gratifying proof of the principle that, with the technology already within reach, we should be able to build a device that is clinically appropriate for patients with speech loss."
How good is it
It is not perfect.
If you listen to this synthesized speech recording:
You may find that it is not crystal clear (the recording says "The proof you are looking for is not available in books").
The system is better with longer sounds like the "sh" in the ship than with abrupt sounds like the "buh" sound in "books".
In experiments with five people who read hundreds of sentences, listeners could see up to 70% of the time what was said when they were given a list of words to choose from.
Who could it help?
Many diseases can lead to speech loss, including:
- Motor neuron disease
- brain injuries
- Laryngeal cancer
- a few strokes
- neurodegenerative diseases such as Parkinson's and multiple sclerosis
The team says it might work on some of these diseases.
However, the technology relies on the parts of the brain that control the correct functioning of the lips, tongue, voice box, and jaw. Patients with certain types of strokes can not benefit from it.
"This is not a solution for anyone who can not communicate," says Prof. Chang.
The prospect of helping people who have never spoken, including some children with cerebral palsy, to help them learn to speak with such a device is also possible from a distance, say the researchers.
What do people have to think?
Participants in the study were instructed not to make specific mouth movements.
Professor Chang said, "It was only asked to read some very simple sentences.
"So it's a very natural process that the brain translates into movement itself."
Can unscrupulous people read my private thoughts?
At the moment it is too hard.
Professor Chang said, "We and others have actually tried to examine whether it is possible to decode only thoughts alone.
"And it turns out to be a very, very difficult and challenging problem.
"That's just one reason why many of us focus on what people really want to say."
However, some scientists have argued that there is an ethical debate about brain-machine interface technologies that read the mind.
What do the experts say?
A commentary released alongside the investigation said the results were "convincing."
It added, "We can hope that people with speech disorders will have the ability to freely express their thoughts and reconnect with the world around them."
Professor Sophie Scott of University College London said, "This is a very interesting work from a great laboratory, but it must be noted that it is at a very early stage and not yet near clinical applications."
Follow James on twitter.