Given a choice, a newborn will choose sound patterns heard in the womb.

With a high-tech pacifier, a baby can choose between sounds by changing sucking rate.

The first time I played my acoustic guitar for my son, Michael, he was just a few months old. But even though the only other occasions he could have heard me play was when I was pregnant with him, he turned around and gave me a smile that seemed to say, “I recognize that sound!” Was it possible that he was remembering what he had heard in the womb?

For years, doctors assumed that babies were born without any knowledge about the outside world. But recent research is questioning this assumption, offering clues to what babies comprehend in utero, what they remember after they’re born, and how that information prepares them for the world outside the womb. Today, doctors realize that babies begin to engage many of their senses and to learn about the world around them during the last trimester of pregnancy—and maybe even before.

Click here to read about the MIT process for measuring infant sucking rate

What’s That Noise?

The uterus isn’t exactly the quietest place to hang out. Not only can a baby hear the sounds of his mom’s body—her stomach growling, her heart beating, the occasional hiccup or burp—but he can also hear noises from beyond. If mom sits in a movie theater with state-of-the-art sound or walks by a noisy construction site, odds are the fetus will react to all the ruckus by kicking or shifting around.

Of course, not all sounds are the same. Perhaps the most significant one a baby hears in utero is his mother’s voice. Around the seventh and eighth month, a fetus’s heart rate slows down slightly whenever his mother is speaking, indicating that mom’s voice has a calming effect.

By the time they’re born, babies can actually recognize their mother’s voice. In one study, doctors gave day-old infants pacifiers that were connected to tape recorders. Depending on the babies’ sucking patterns, the pacifiers either turned on a tape of their mother’s voice or that of an unfamiliar woman’s voice. The amazing result: “Within 10 to 20 minutes, the babies learned to adjust their sucking rate on the pacifier to turn on their own mother’s voice,” says the study’s coauthor William Fifer, Ph.D., an associate professor of psychiatry and pediatrics at Columbia University’s College of Physicians and Surgeons. “This not only points out a newborn’s innate love for his mother’s voice but also a baby’s unique ability to learn quickly.”

Interestingly, there is no evidence that newborns show a similar preference for their father’s or siblings’ voices, or for any other voices they may have heard frequently while in the uterus. “The difference could be that the maternal voice is communicated to the fetus in two ways: as ambient sound through the abdomen and internally through the vibration of vocal chords,” says Janet DiPietro, Ph.D., a developmental psychologist at Johns Hopkins University. “In contrast, external voices and other noises are only heard as ambient sounds.”

In fact, research has shown that if newborns are given a choice, they prefer the version of mom’s voice that sounds closest to what they heard in the womb. “In studies where we gave day-old babies a choice of hearing their mother’s voice filtered to sound as it did in utero—muffled and low—or as it does outside of the womb, they showed a distinct preference for the filtered voice,” says Fifer.

An Ear for Language

Muffled or not, unborn babies seem to develop a fine ear for certain sounds. Research reveals that babies had their first lessons in their native language while still in utero. They’ll suck more vigorously to turn on tape recordings of people speaking in the language of their mothers, rather than in a foreign tongue. Of course, it’s likely the babies are picking up on the rhythm and melody of the speech, rather than individual words.

This doesn’t mean that moms need to converse directly to their swelling belly to give their child a head start on language, however. A developing fetus gets all the information he needs just by listening in on his mother’s conversations with others. He also may be picking up something from any books she reads aloud. Besides being able to tell the difference between English and French, a study shows that babies in the womb may be able to recognize the specific rhythms and patterns of the stories they hear. Pregnant women read out loud one of two stories—The Cat in the Hat or The King, the Mice, and the Cheese—twice a day for six weeks before they delivered their babies. After birth, when the infants were three days old, they were played tape recordings of unfamiliar voices reading those stories: They consistently changed their sucking patterns on the pacifiers to hear the story they’d heard in utero.

To read the rest of this article, which turns from the language aspects of pre-natal learning to such things as babies’ perception of light while in the womb, click here.

Click next page to see how deeply embedded in the infant’s prenatal consciousness is the melody of their native language, or languages.