Terri Schiavo's eyes look vacant. Her mouth hangs open. Then, her mother approaches, saying, "Hi, baby," in a bright voice. Schiavo's lips turn upward, and her blinking accelerates.

What do these carefully edited video clips reveal about the severely brain-damaged woman?

Nothing of any real significance, medical experts say.

Therein lies one of the most difficult-to-grasp facets of this controversial right-to-die case. What appears on the surface to be intelligent, intelligible behavior on Schiavo's part is anything but, most physicians say.

To the contrary, the 41-year-old woman is capable only of meaningless, spontaneous responses arising from the deepest, most primitive centers of her brain, experts suggest.

"Her facial muscles may move, but there's no feeling behind it," says Dr. Ronald Cranford, a neurologist who examined Schiavo in 2002 and reviewed all her medical records. "Everything you see is reflex."

Schiavo's parents don't agree. Where doctors see muscles moving involuntarily, they see their daughter smiling. What experts call instinctual, animal-like reactions - Schiavo's face turning toward her mother as she speaks, her eyes seeming to scan - her parents deem signs of her feeling presence.

By releasing videos of their daughter for the world to watch, Schiavo's parents have appealed powerfully to the court of public opinion. But the pictures are extremely misleading, experts warn. Some physicians believe there is evidence that Schiavo may have some degree of consciousness, but they are in the minority.

"These are some of the most powerful images we've seen in American bioethics," said Laurie Zoloth, professor of medical humanities and bioethics at Northwestern University's Feinberg School of Medicine. "It's one of the extremely painful features of this case - that it looks so much like Schiavo is responding, yet everything that neurologists tell us is she cannot respond."

Scans have shown extensive damage to Schiavo's cerebral cortex, a part of the brain essential to higher-level functions such as cognition and consciousness. An electroencephalogram, which examined patterns of her brain's electrical activity, documented virtually no normal response.

Because Schiavo's brain stem has remained largely intact, however, certain automatic body functions - sleeping and waking, breathing, metabolizing nutrients, and others - go on.

Blinking, startling in response to a stimulus, changing facial expressions and making occasional sounds are also among the body functions controlled by the brain stem.

"The part of the brain responsible for these responses - smiling, crying, chewing, moaning - is still working. But the part of the brain responsible for thinking is not," said Dr. Ghada Ahmed of the Rehabilitation Institute of Chicago.

Medicine calls this a "vegetative state" and considers it permanent and irreversible if a patient remains in this condition for more than a year without signs of improvement. Schiavo has been severely brain-damaged for 15 years.

Crucial to the diagnosis is a thorough assessment of how aware a patient is of herself and her environment. That requires prolonged observation and extended conversations with family members and other caregivers, said Dr. Roger Albin, professor of neurology at the University of Michigan.

In Schiavo's case, "if you look at her eyes, she doesn't track or make contact," said Cranford, who observed her clinically for 42 minutes in 2002. "If you ask her to do something, she can't do it. She smiled and grimaced, but it had nothing to do with me. She does it spontaneously."

The Chicago Tribune is a Tribune Publishing newspaper.