Mind & Brain / Early Language

Rebecca looks bizarre with brain-imaging gizmos attached to her little bald head—like a baby who has crept into Dr. Frankenstein’s lab. A white terry-cloth headband holds two plastic squares against either side of her skull. Each contains a set of black rods with a welter of wires. Rebecca seems oblivious to the headgear as she turns her head from side to side with a wet, toothless grin. She isn’t yet five months old, but according to Laura-Ann Petitto, a cognitive neuroscientist at Dartmouth College, she is already using the parts of her brain involved in language. And the contraption on her head is designed to let Petitto watch her do it.

Photograph by Dirk Anschütz At Dartmouth College, laser light is beamed into a baby's head. Researchers analyze reflections from the laser for signs of brain activity during babbling.

Known as near-infrared spectroscopy, this technology is designed to show which part of the brain governs a given behavior by measuring where the brain uses the most oxygen. Petitto is learning how to use the device, and in time she hopes to zero in on an area just above the left ear that may play a prominent role in language acquisition. “Language is the looming contributor to this thing we call consciousness, which is at the heart of reason, emotion—the individual,” she says. “Think about what we’re doing right now. I’m sending sound waves through the air. I’m not even touching you. Yet you have explosions of meaning in your head. By what mechanism does our species accomplish this truly astounding feat?”

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For a scientist trying to answer this question, babies are the ultimate black box. They can’t explain a word of what’s happening inside their small developing brains, yet that’s where language—with all its complexities of grammar and vocabulary—is born. “You wouldn’t expect babies to be better than adults at anything,” says Jenny Saffran, director of the Infant Learning Laboratory at the University of Wisconsin at Madison, “but they are better at learning language.”

Babbling—the stringing together of repetitive syllables, as in da, da, da, da, da or ga, ga, ga, ga, ga—is one of the earliest stages of language acquisition. Babbling allows babies to learn and practice sounds they will one day use to create language. And so scientists have listened to babies babble, and they have watched babies babble. And if this new spectroscopy lives up to its promise, they may soon be able to watch babies’ brains operate as they babble.

Babbling is universal. No matter where babies are born or to which language they’re exposed, they begin—between 5 and 10 months of age—to rhythmically repeat syllables. Coincidentally, they often accompany themselves with equally rhythmic movements of their hands and feet. Petitto says they’re especially fond of shaking their right hand, or a rattle, while they babble.

“People used to think that language grew from our capacity to produce and hear speech,” Petitto says. “If that were true, then a child who is stripped of speech should learn language in a different way.” In fact, she says, babies can even babble in sign language.

			Brain scans show that Broca’s area, located behind the left temple, helps us produce language and understand grammar while Wernicke’s area, just above the left ear, helps receive language and decipher its meaning. It’s still not clear when these language centers develop.

A few years ago, Petitto and her colleagues attached light-emitting diodes to the hands of babies learning to sign and others learning to speak. An electronic device recorded the trajectory, velocity, and frequency of the babies’ hand movements. Both groups, Petitto found, made rhythmic hand gestures with a frequency of about 3 hertz—three complete movements a second. But the babies exposed to sign made a second kind of movement as well, this one with a frequency of 1 hertz, or roughly one second.

The timing is significant because it’s almost equivalent to the length of one unit of spoken babble: da, da, da, da, da. To Petitto, this suggests that language grows from a part of the brain that can work with either sign or sound—one that is wired to register the bursts of aural or visual communication that are the building blocks of words. “A baby finds delicious, and is very powerfully attracted to, anything that has these rhythmic undulations,” she says.