Andrew Meltzoff spends a lot of his time making faces at babies.

He sticks out his tongue. He opens his mouth. He protrudes his lip.

And he watches what happens.

The babies stick out their tongues, open their mouths, protrude their lips.

We're talking very young babies, here too. Days old. Hours old. In at least one case, minutes old.

This is not supposed to happen. It is contrary to some dearly held beliefs of child development specialists. It even challenges some of the precepts set forth by the late Swiss psychologist Jean Piaget, who revolutionized thinking about the early years of human emotional, social and cognitive development only a few decades ago.

Piaget said -- and it became etched in psychological dogma -- that children should be unable to imitate before they are about a year old.

So not surprisingly, it became controversial when Meltzoff published his first report on two- and three-week-old babies imitating face-making adults (mainly Meltzoff himself) about eight years ago in the journal Science.

In the succeeding years, Meltzoff, at the department of experimental psychology at Oxford University and more recently at the Child Development and Mental Retardation Center at the University of Washington in Seattle, has been able to replicate and confirm his earlier findings.

And in addition, he has been able to show that the ability to synchronize different senses -- for example to touch or hear something and later on identify it by looking at it -- occurs at a much earlier age than had previously been thought.

This ability to process information using more than one sense, is known to specialists as "cross-modal matching," or "active inter-modal mapping." Most specialists believed that this perceptual skill was acquired slowly as the infant developed and did not normally occur until months, perhaps even a year, after birth.

"We can now say with confidence that the capacity to imitate facial gestures is part of man's innate endowment and does not depend on learned associations," Meltzoff said at a meeting of the National Center for Clinical Infant Program training institute here earlier this month.

Some of Meltzoff's most recent work, published in the journal Child Development, shows that "even newborn infants [one of them only 43 minutes old] can imitate facial gestures."

"What we find out about imitation has direct and important implications for theories of infant perceptual, cognitive and social development," Meltzoff said. His work shows that babies are innately able to process information from their environment much sooner than anyone believed and are therefore able to learn earlier.

Meltzoff also determined that 12 to 21 day-old babies could imitate facial expressions even when their response was delayed until after the demonstration was ended. To keep the baby from imitating too soon, Meltzoff said, "we simply put a pacifier in the baby's mouth while we did the gestures . . . Then we stopped doing the gestures, assumed a passive face and only then pulled out the plug and let the baby respond."

Again there was a high rate of infant response. As soon as the pacifier came out, the tongue came out or the mouth opened or the lip protruded, depending on the earlier adult gesture.

In order to eliminate the possibility that the infants had not previously seen an adult making faces or were not responding to some sort of innate instinct, Meltzoff tried another experiment. He wanted to test whether infants can associate specific sounds with specific facial expressions demonstrating an ability of the infants to associate information received by one sense with identification using another. This would indicate a more complex central nervous system organization.

To test this, he studied 32, 4-month-old babies who were propped up -- one at a time -- in infant seats in front of a panel that displayed a photograph of an adult with his mouth open as he says "ahhh," and another photograph with an adult saying "eeeee." There was a speaker between the two photographs.

In a few minutes, the infants learned to associate the sounds with the correct facial expression when one sound was presented with one picture. But then, when both pictures were shown, but only one sound came through the speaker, the infants consistently looked at the picture of the adult articulating that sound.

The experiment shows, he said, that 4-month-old infants already have elementary perceptions of speech and language and can associate sounds and sights. And it suggests that babies are "wired" at birth for this sort of almost immediate interpretation of sensory input. That seems to support the nature side of the eons-old nature versus nurture argument.

On the other hand, Meltzoff's work also supports the nurture side because the infants demonstrate their ability to learn. As the newborns practice sticking out their tongues, protruding their lips and opening their mouths, imitating an adult, they get better and better at it.

Nature versus nurture is a debate that continues in many areas. At the NCCIP institute, its relationship to early infant development was the topic of a "dialogue" between two major figures.

But there was clearly more agreement than disagreement between Dr. Jerome Kagan, of Harvard University and author of "The Nature of the Child," and Dr. Stanley Greenspan, pioneering psychiatric specialist in infant and child development, and author, with his wife, Nancy Thorndike Greenspan, of "First Feelings, Milestones in the Emotional Development of Your Baby and Child from Birth to Age 4."

Kagan, representing the nature side of the argument, noted that the debate, whether called environment versus heredity, nature versus nurture, genetic determinism versus cultural adaptation or psychobiology versus experience, goes back to Plato and Aristotle or earlier.

Greenspan represented the nurture side of the argument that was described (in a vast oversimplification) in this sentence: "love alone is not enough, but without love everything else together isn't enough."

Kagan is more concerned with the development of the central nervous system itself, and the inability of the baby to retrieve memory until late into the first year of life. Indeed, he notes that not-yet-published research on the development of the central nervous system in monkeys will demonstrate that "in all areas of the cortex [the higher learning centers of the brain,] the growth of synapses [the connections between brain cells] reaches a peak at two months." As a rule of thumb, scientists multiply by 4 to find the comparable age in a human baby -- in this case, 8 months. So before 8 months, he said, the baby cannot recall early experiences because the brain is not wired to remember them.

But for Greenspan, emotional development is of greater concern. And emotional development, his school of thought holds, is a product of early interaction between the infant and a parent or other primary caregiver.

For example, says Greenspan, without a partner, "how does the 8-month-old know that reaching out leads to being held? How do they learn about dependency, that certain forms of aggression lead to limit setting . . . Here they need a sensitive, reciprocal, social partner" rather than -- or along with -- fully developed memory pathways.

Kagan said he agreed that "an emotional, joyful, loving interaction between parents and infants is one of the great experiences in our brief lives," but he would concede only that it is "probably beneficial for infants."

His concern, he said, is that too much emphasis is put on parent/child interaction in the early months of life. "There is a danger that if you assume all the power for a child's success in school, character development, ability to love is built up in the parent-child interaction, then you ignore a whole set of factors outside the family, tied to class and neighborhood and school, and you end up blaming poor mothers who love their children."

Nevertheless, said Greenspan, the things that "have to do with the essence of humanity -- to trust, to love, control impulses, share, test reality -- these are all learned or not learned in the early years."