By the time she was 9 months old, my daughter Grace knew that she should raise her arms when I asked, "How big are you?" "So big!" I'd say, laughing as I pulled a clean shirt over her head. She couldn't have known I was referring to her size, but by a process of repetition and imitation she learned that the question meant it was time to put on a clean shirt.
At 16 months, she'd say, "Bo bee" -- her version of "So big" -- to indicate that she wanted to put on a shirt that she'd retrieved from the laundry basket. By listening, remembering, and imitating, she'd learned cause and effect, to connect words with actions.
By 18 months, Grace lifted her shirt to reveal her Buddha belly, an attribute that had been often praised by her parents. She spoke her first sentence: "I big belly." Although she still doesn't associate the question "How big are you?" with her size, it seems that in a separate process, she has learned the concept of "big," and accurately used it to describe her stomach.
Before a toddler learns to speak, we grasp for any clue to personality or intelligence, asking ourselves, "What do you suppose is going on in that little mind?"
LET THE LEARNING BEGIN
Part of the scientific answer is that 100 billion neurons are "hard-wiring" the baby's brain -- each neuron is producing fibers that transmit signals to thousands of other neurons. For instance, when a 2-month-old baby tracks a toy with his eyes, it's a sign that areas of the brain relating to vision are "wiring up."
But each bit of information from the baby's environment, and each experience, reinforces particular neural connections. In the first two months alone, the number of these connections increases from an estimated 50 trillion to 1,000 trillion.
Compared with most other species, humans have a huge number of brain cells. "It's as if nature decided, We want to have these guys with enormous brains, but we can't make their bodies six times larger, so we're going to cut pregnancy short and get these things out before the head becomes too big," says Alan Leslie, Ph.D., a cognitive-development researcher at Rutgers University. As a result, human babies are born with immature brains, creating what Leslie calls "the great learning species."
The learning starts with the sounds and sensations a baby experiences right before he is born. At birth, the sense of hearing is more developed than vision. "Full-term infants have the benefit of having heard their mother's voice for the weeks preceding delivery," says Charles Nelson, Ph.D., professor of child psychology, neuroscience, and pediatrics at the University of Minnesota's Institute of Child Development, who has monitored newborns less than 24 hours old and found that when they hear their mothers' voice, they show a different pattern of brain activity than when they hear a stranger's.
Outward evidence of brain work is subtle at first: the newborn modifying his sucking to adapt to the breast, bottle, or pacifier; the 3-week-old baby who takes a break from feeding to look into her mother's eyes. Because a newborn's vision is believed to be no better than 20/400, he is more attracted to stark contrasts, such as black and white. But when the connections between the neurons in the visual cortex increase dramatically, between 2 and 4 months, an infant begins to see more clearly. That, plus his developing depth perception, may explain why he now notices more-detailed pictures and toys. By the time babies are 2 to 3 months old, they'll begin watching people as they walk across the room. By 6 months, vision improves to 20/40 or better.
Nelson believes that the ability to recognize caretakers, which occurs at about this point, is a primitive understanding of cause and effect: "When I'm hungry, one of them feeds me," posits the baby brain. An infant may look across the room toward the refrigerator, because she's learned that bottles come from there. Breast-feeding mothers are likewise objectified.
By 4 to 5 months of age, a baby will visually follow an object -- such as a spoon or a rattle -- when it falls out of her hand, which solidifies her growing understanding that things exist even in motion. Simple hiding games and rounds of peekaboo reinforce the idea that objects, and Mommy, still exist even when they're out of view.
CRACKING THE CODE
After just a few months, babies are ready for diversions. Though the level may be primitive, the "awakening" usually strikes parents as nothing short of miraculous. Mackenzie Ekren, of St. Louis, is only 6 months old, yet she has learned the give-and-take of conversation. "Her tone varies," says her mother, Amy. "It isn't a monotone like I thought it would be." Often, Mackenzie will pause to wait for a response. If there is none, she arches her eyebrows, which her mother takes to mean, "C'mon. Say something!" Sometimes her mother holds up her end of the conversation, other times she imitates her daughter's babbling, which Mackenzie interprets as a fun competition -- she mimics her mother right back and tries to outtalk her.
Such interactions indicate huge strides in cognitive development. "A baby is beginning to crack into the huge world of encoded communication that flies around -- what we call language," says Leslie. As the baby's babbling becomes more distinct (between 8 to 10 months), parents begin to wonder if she is actually forming words: "mama," "dada," or even complex phrases.
By babbling, a baby practices forming the varied sounds of her native language, with parents often trying to help their child along. When Margie Gitten, of Holmdel, NJ, points to the polka dots on the nursery wall, she names each color for her daughter Emily, who is 7 months old. Although Emily cocks her head and looks as if she's registering the information, her mother isn't sure what, if anything, Emily is learning. But Emily can't help but gain knowledge -- if not of colors, then certainly of the fact that she's worthy of her mother's doting attention.
By 8 months, babies are beginning to retain words in their long-term memory. In a recent study, researchers had infants that age listen to stories, then two weeks later read back lists of words to them. Measuring the amount of time each baby stared at a flashing light, they found that the babies listened to words taken from the story significantly longer than they listened to unfamiliar ones. As far as scientists can tell, 8-month-olds don't attach much meaning to words, although sound retention continues to be an important way for babies to learn language.
As an infant's physical relationship to the world moves from lying down to sitting, crawling, and finally, walking, it's difficult to separate cognitive development from motor development. Now a baby has the freedom to change his point of view and perspective. "This has an enormous impact in terms of how much useful information the infant can obtain," says Leslie, who compares this advantage to adding a zoom lens to your camera. "If the baby wants to zoom in on something, now he can stand up and walk toward it. He can even pick it up and put it in his mouth for good measure. Being able to move around allows the baby to bring that fantastic brain into contact with more and more of the world."
WINDOWS OF OPPORTUNITY
In the recent spate of news reports about a baby's developing brain, much has been made of the idea that there are "critical periods" of cognitive development. Reading that, you might be inclined to believe that if you didn't try to provide intellectual stimulation at all times -- as if such a thing were possible -- you'd miss your window of opportunity and your baby would suffer irreparable setbacks.
"Without a doubt, the first few years of life are critical for some aspects of brain development," says Nelson. Visual development, for instance, usually occurs during the "critical period" between the second and fourth months. Likewise, if a newborn learns that no one comes when he cries, his emotional development may be stifled.
Nelson prefers the term "sensitive" in place of "critical" periods, and stresses that even if a baby misses out on an important cognitive step, the outcome will depend on his individual constitution. While some kids are unable to compensate for early deficits, he says, "there are children who develop well despite adversity."
Of course, we want no adversity for our children, no window of opportunity slammed shut. So we play nursery games, read simple books, make funny faces. The neurologist might say that with each round of peekaboo, a particular neural connection is reinforced. The cognitive-development theorist might counter that during the appropriate developmental stage, a baby moves to the next logical step. Both would agree that the net effect of peekaboo is the same: A baby comes to understand that among the known properties of his physical universe, his parents considered him worthy of their time, love, and attention.
Despite the complexities of the developing brain, despite all that science has yet to discover, there is one great secret a baby will reveal. Day by day, he'll let his parents know who he is, and offer clues, imperceptible at first, as to what is going on in that little mind. It's a mystery that is quickly revealed, for by the time he is a toddler, few of his thoughts are likely to go unexpressed.
Linda Henry, the mother of two, is the editor of The Talking Stick, a literary journal.