He said Houben started out with a yes-no system before moving to the touch screen, and returning to it would be extremely limiting. He added it would be strange for Houben's mother not to have noticed anything wrong over the three years he has been communicating again.
Nicolaes said she is convinced her son speaks to her and appreciates the jokes and "black humor" that lace his sentences.
Laureys's team is in the process of producing a scientific study validating the controversial practice. He refused to discuss it in the media, saying he will follow the classical route of scientific peer reviews and publication in specialized journals before making it public to the world at large.
He hopes it will be ready "in the not too distant future."
The next challenge for Houben is to continue improving his movement by tiny steps so that one day, he might even write without an aide, said Laureys.
"We talk about small movements, a tiny control of the finger. But it can mean a lot for him. He might control his wheelchair or his computer," he said.
AP Medical Writers Malcolm Ritter in New York and Maria Cheng in London contributed to this article.
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