Inner voice learns to talk

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It might seem the stuff of science fiction, but a mind-reading device is being developed by scientists which can eavesdrop on your inner voice.

Researchers at the University of California, Berkeley, have developed a machine and computer programme which converts brain activity into sounds and words.

Speech activates specific neurons as the brain works to interpret the sounds as words. Each word activates a slightly different set of neurons.

Now scientists have started to develop an algorithm that can pick up the activity and translate it back into words in the hope it might help people who are unable to speak.

"If you're reading text in a newspaper or book, you hear a voice in your own head," Brian Pasley told New Scientist magazine.

"We're trying to decode the brain activity related to that voice to create a medical prosthesis that can allow someone who is paralysed or locked in to speak."

The team recorded the brain activity of seven people undergoing epilepsy surgery while they looked at a screen displaying the nursery rhyme Humpty Dumpty, the Gettysburg Address or the inaugural speech of President John F Kennedy.

Their brain activity was monitored as they read aloud the text and when they read it silently in their heads.

From the spoken data the team managed to build a personal "decoder" for each patient which interpreted the information and turned into a visual representation.

They then applied the decoder to brain activity during silent reading and found that they could reconstruct words that were being thought through neural imaging alone.