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Their brain typing system uses functional magnetic resonance imaging (fMRI) to analyze the hemodynamic responses in the brain—the movement of blood inside our gray matter. These responses are caused by mental images that get tied to each letter of the alphabet using computer analysis algorithms.
Once the computer is up and running, the patient can freely type letters, one after the other, using their brain. Each alphabet letter corresponds to one of 27 "reliable and differentiable single-trial fMRI signals."
In each communication experiment, participants held a mini-conversation consisting of two open questions and answers. Everyone the researchers tested was able to successfully produce answers within a single one-hour session.
The results substantially extend earlier uses of fMRI, which allowed individuals to answer the equivalent of multiple-choice questions having four or fewer possible answers, by enabling free-letter spelling. That could make all the difference for people who are completely paralyzed and unable to benefit from other means of alternative communication, Sorger says.