An example of a device of the type used to record brain activity in the current study.

A computer that aims to translate thoughts into natural sounding speech has been hailed by its developers as an "exhilarating" breakthrough.

Researchers from the University of California, San Francisco, designed the system – a computer simulation that turns brain signals into a virtual voice – to help restore speech to people with paralysis or neurological damage. They published their paper in the scientific journal "Nature" on Wednesday.

The device works by using a brain-computer interface (BCI), which works out a person's speech intentions by matching brain signals to physical movements they would usually activate in a person's vocal tract – their larynx, jaw, lips and tongue. The data is then translated by a computer into spoken words. The same technique has been used to generate limb movement in people with paralysis.

Previous BCI systems for speech facilitation have focused on typing, generally allowing people to type a maximum of 10 words per minute – massively lagging behind the average speaking speed of around 150 words per minute.

Scientists worked with five volunteers whose brain activity was being monitored as part of a treatment for epilepsy. The researchers recorded activity in a language-producing region of the brain as the volunteers read several hundred sentences aloud.

Researchers working on the project claimed their computer system would not only restore speech, but could eventually reproduce the "musicality" of the human voice that conveys a speaker's emotions and personality.