Washington, D.C. ? South Dakota Sen. Tim Johnson has been exceeding expectations in his recovery from emergency brain surgery last week, his son Brendan said Tuesday.

Brendan Johnson, a Sioux Falls lawyer, said his father has been responding repeatedly to directions from his mother, Barbara. But he is not yet speaking.

“It’s fair to say he’s been exceeding expectations up to this point,” Brendan Johnson said. “All the tests and the indications now are positive.”

Johnson offered few details about his father’s condition and said he doesn’t know what kind of tests he will undergo this week. He said he is not sure if the senator will need additional surgery.

The senator’s sudden illness raised questions about the Democrats’ one-vote majority in the upcoming Senate session.