They say film doesn't lie, but does that mean it tells the truth?
The public sees fleeting videotaped images of Terri Schiavo (search), appearing to many to turn toward her mother's voice and smile. They hear what sound like moans and laughter. They watch her head move up and down, seemingly following the progress of a brightly colored Mickey Mouse balloon. And often they ask: How could anyone conclude but that she is aware of her surroundings?
The answer lies not so much within Schiavo's brain as in the minds of those who observe her.
As social beings, humans are hard-wired to examine another's face for clues to what the person behind it is thinking. They naturally associate vocal tones with specific moods. They detect meaningful words in nonsense utterances.
"I can understand that, because I have examined scores, if not hundreds, of people with this condition," says Dr. Leon Prockop, a professor of neurology at the University of South Florida (search), who has reviewed the brain-damaged woman's CAT scans.
At first, he says, his "natural emotional desire to be optimistic and hopeful" made him interpret movements and facial expressions as purposeful. But after long experience, Prockop says, "I came to realize that my emotional reaction was understandable as a human being, but was not an intellectual assessment."
The public has seen only a tiny portion of the more than four hours of videotape shot during the past seven years of litigation over whether to keep the 41-year-old woman on a feeding tube.
Even doctors who have agreed that she is in a persistent vegetative state have admitted to being swayed, if only briefly, by the now familiar images that have been played and replayed on national television.
During testimony in a 2002 hearing, court-appointed neurologist Peter Bambakidis acknowledged that seeing the videotapes of Schiavo's mother kissing and speaking with her gave him pause at first.
"Yes, that was a source of the concern on my part: How does one interpret a situation like that?" he said. He even acknowledged that she did track a Mickey Mouse balloon with her eyes in one clip.
"I was concerned as to whether or not there may have been some minimal consciousness there," he testified.
But Bambakidis noted that such visual tracking "commonly occurs spontaneously in people in a persistent vegetative state." After reviewing her brain scans and visiting with her, he came to the conclusion that she had no hope of recovery.
Dr. James Barnhill, a neurologist hired by Michael Schiavo, the husband who has fought through the courts to honor what he says would have been his wife's wishes, reviewed the videotapes and came to a similar conclusion.
Barnhill has said Terri Schiavo engaged in "pathological laughter, pathological crying ... consistent with the vocalizations that are seen in people with persistent vegetative states. I see nothing on that tape that indicates an awareness there or consciousness."
William Hammesfahr (search), a neurologist hired by Terri Schiavo's parents, looks at the same tape and sees a woman who is clearly reacting to her mother, turning toward her voice, smiling and appearing to sing when she hears familiar piano music.
"She is absolutely responding to her mother," he testified. "There's no doubt."
To understand the emotional reaction to the tapes of Terri Schiavo, one need only spend a few minutes with Kismet.
People who spend time with the robot at a Massachusetts Institute of Technology (search) lab walk away feeling like they've made a new friend.
Kismet is nothing but a mechanical head made out of metal and plastic, but it has been cleverly programmed by scientists to mimic human social interactions.
Sit down across from Kismet and it gives you a pleasant smile. Step too close and it jumps back with a startled expression on its face. Introduce yourself and it waits patiently for you to finish talking, then replies with a few syllables of speech that sounds like a higher-pitched version of the language spoken by the teachers in 'Charlie Brown' cartoons.
Kismet is no more conscious than a dishwasher or a microwave oven. But its vaguely human behavior has a powerful effect on brains that are predisposed to attach meaning to gesture, facial expression and vocal tone.
"This ... system that we have is so automatic and so powerful, sometimes it ends up being triggered by things that aren't people and don't have minds at all," said Martha J. Farah, a psychologist at the University of Pennsylvania. "It's very hard to suppress the impression that there's somebody there."
People in persistent vegetative states are no more aware than Kismet, but they retain a handful of primitive reflexes that are naturally misinterpreted as conscious behavior.
"The mere noise of walking will make the eyes flicker," said Lawrence J. Schneiderman, a professor at the University of California, San Diego (search) medical school who specializes in the bioethics of medical futility and end-of-life care. "And there may be a grimace, so the relatives will say, 'Oh, she's happy to see me.'"
But all of those apparent signs of awareness are the product of a brain so damaged that by medical definition it has no capability of thought, no sensory awareness, no sense of its own existence in the world.
In Schiavo's condition, only the most primitive part of the brain survives. That region, known as the brain stem, merely sustains the vital functions of breathing, heart rate, sleep-wake cycles and primitive reflexes such as coughing and blinking.
"I think the term should be permanent unconsciousness," Schneiderman said.
Prockop prefers the phrase "coma vigil."
"If you put your finger in their hand, they reflexively grasp it," he says. "The analogy can be made to infancy."
But while a newborn's frontal lobes are present but undeveloped, Schiavo's frontal lobes are damaged beyond repair, Prockop says.
Prockop says the video clips he's seen are consistent with a diagnosis of coma vigil. But he cautions that he would not use them to make a diagnosis.
"You can't take these clips out of the context of examining the individual and seeing a long monitoring film," he says. "They don't give you enough information."