Six weeks into rehabilitation after suffering a gunshot wound in the head, Rep. Gabrielle Giffords (D-Ariz.) is able to follow conversations and instructions, occasionally speak in full sentences, express emotion and walk with assistance, her physicians reported Friday.

In a news briefing that was almost entirely upbeat, the doctors at TIRR Memorial Hermann hospital in Houston said they were surprised by the rate of Giffords’s progress and noted that she was not discouraged or depressed.

“I am very happy to report she is making leaps and bounds in terms of neurological recovery,” said Dong Kim, one of the neurologists on her team. “She has made a tremendous amount of progress.”

He stopped short of assuring that Giffords would be able to watch the April 19 launch of the space shuttle, which her husband, Mark E. Kelly, will command.

“We think there’s a good possibility that she will be there,” he said. But the rehab team needs to be sure such an excursion would be both “safe and appropriate.”

A breathing tube inserted in a tracheostomy, or opening in the front of her neck, was removed last week, which Giffords celebrated with a pumped fist, said Imoigele Aisiku, a critical care physician at the hospital.

Giffords was wounded in the left side of her head Jan. 8 in a mass shooting that killed six people and wounded 12 others besides her. The left side of the brain controls language — both speaking and comprehension — in nearly all people.

Kim said Giffords “is clearly saying words she wants. She is starting to string words together. She can repeat anything we say to her.” That last capacity is especially important, he said, because it implies that the “whole primary language area” is intact. However, he did not provide examples of the kind or complexity of verbal tasks she is performing.

Giffords has no memory of the shooting and would not be expected to remember it, the doctors said. She’s been told about it and knows it is the cause of her injury. Her memory otherwise appears to be normal, both for remote events (such as experiences of childhood) and recent ones (such as day-old conversations).

“We don’t think she is going to have any memory problems outside of that one event,” Kim said. He added that they don’t expect her to have vision problems, either.

Giffords is undergoing three to five hours of therapy a day at the Institute for Rehabilitation and Research (TIRR), a 119-bed rehab center in the huge, multi-hospital Hermann health-care system in Houston.

Gerard Francisco, a rehabilitation physician and TIRR’s medical director, said the staff has “been kept busy reimagining and rethinking the rehab program” because of the congresswoman’s progress. That consists of adding new forms of therapy and making the ones she’s already doing more difficult and complex. But he did not provide examples.

Francisco and Kim said Giffords’s personality — she is known for enthusiasm and optimism — is apparent.

“She hasn’t shown depression,” Kim said. “She’s been just very forward looking, and even with the speech, she’s not showing much frustration.”

Francisco said Giffords “gets excited when there’s an accomplishment. We know that she knows when she has accomplished an important milestone.” He added, “I feel I know her very well.”