On Sunday night, as Congress took up debate on her case, her father told reporters that she responded to his teasing by making a face at him. "It tells us she's still with us," he said.
But in Schiavo's condition, described as a persistent vegetative state, family members can be deceived by things like eye movements and reflexes, experts say.
"It creates this ironic combination of wakefulness without awareness," said Dr. James Bernat, a neurology professor at Dartmouth Medical School.
That's because in a persistent vegetative state, the brain centers that control wakefulness are functioning, but those that permit conscious awareness of oneself or the environment are damaged or destroyed.
As a result, patients close their eyes to sleep and open them when they wake up. If a doctor brushes the eyeball with a wisp of cotton, they may blink. If something gets caught in the throat, they will cough. There may be limited eye movements, though patients can't follow a person walking from one side of the room to another, for example.
That's in contrast to a coma, in which the eyes remain closed and a person is neither aware nor awake, or brain death, in which there is no sign at all that the brain is functioning.
Bernat, past chairman of the American Academy of Neurology's Ethics, Law and Humanities Committee, declined to comment specifically on the Schiavo case. He said outward signs of persistent vegetative state can give family members false hope.
"There's a normal tendency of family members to interpret (random) movements as evidence of awareness," said Bernat, who recalled seeing that happen with his own patients.
He said that when family members claim that a loved one in a persistent vegetative state is purposefully looking at them, he asks to accompany them to the bedside and see for himself. Sometimes, in fact, family members really have noticed genuine signs of consciousness and investigation shows the diagnosis was incorrect, he said. But in his experience, Bernat said, most of the time the family has been wrong.
Nobody can enter a patient's mind and discover what that person is experiencing, he noted. Doctors can only say that despite what family members might believe, "to the best of our ability we cannot convince ourselves there is any evidence of awareness," Bernat said. Doctors try to help the family understand how it's possible to be awake but not aware, he said.
Patients can recover after even a year or two in a persistent vegetative state caused by head trauma, Bernat said, although they generally continue to be disabled. However, he said a vegetative state that was caused by lack of blood or oxygen delivery to the brain and has gone on more than five years is considered permanent.
Schiavo, 41, has been at the center of a long and bitter court battle between her parents and her husband, who wants to remove her feeding tube so she can die.
Court-appointed doctors say Schiavo is in a persistent vegetative state, after her heart stopped beating temporarily 15 years ago, cutting off oxygen to her brain. She did not leave any written instructions about care, but her husband, Michael Schiavo, contends she told him that she would not want to be kept alive artificially. Her parents dispute that, and deny their daughter is in a vegetative state.
Video showing the dark-haired woman appearing to interact with her family has been televised nationally. But a court-appointed doctor has said the noises and facial expressions are merely reflexes.
In caring for a person in this condition, doctors are guided by what the patient would have wanted, Bernat said. Some have indicated they want to be treated while others have said they want to be left to die, he said.
Usually patients can breathe without a ventilator. As in the Schiavo case, long-term care involves a feeding tube to deliver fluids and food to the stomach. If family members ask to stop treatment, the tube is removed or medical teams are instructed not to treat infections, Bernat said.