Until 2003, Mr. Wallis lay in a nursing home in a minimally conscious state, able to track objects with his eyes or blink on command

But on June 11, 2003, he effectively returned to the world when, upon seeing his mother, Angilee, he suddenly said, “Mom.” At the sight of the woman he was told was his adult daughter, Amber, who was six weeks old at the time of the accident, he said, “You’re beautiful,” and told her that he loved her.

“Within a three-day period, from saying ‘Mom’ and ‘Pepsi,’ he had regained verbal fluency,” said Dr. Nicholas Schiff, a professor of neurology and neuroscience at Weill Cornell Medicine in Manhattan who led imaging studies of Mr. Wallis’s brain. The findings were presented in 2006 in The Journal of Clinical Investigation.

“He was disoriented,” Dr. Schiff, in a phone interview, said of Mr. Wallis’s emergence. “He thought it was still 1984, but otherwise he knew all the people in his family and had that fluency.”

Mr. Wallis, who regained some more movement after he was awakened, was diagnosed with severe quadriparesis, characterized by muscle weakness in his limbs.