I am delighted to have a guest post from Author Susan Brink today. Susan’s book, The Fourth Trimester: Understanding, Nurturing, and Protecting an Infant Through the First Three Months, was released a few weeks ago. I really enjoyed this book. It is billed as an “operating manual” for newborns, but it read to me more like an “understanding manual.” This is actually more helpful, because if you can understand why your newborn is doing the things she’s doing, you’re on your way to figuring out how you and your baby will survive and thrive in this period. The Fourth Trimester includes chapters on crying, sleeping, feeding, sound, sight, touch, physical development, and stimulation. Each is full of both science (well-cited, I might add) and stories from real parents. The sight and sound chapters were two of my favorites, so I’m happy that Susan chose these topics for her guest post on Science of Mom. Enjoy!
WHAT THE WORLD LOOKS AND SOUNDS LIKE TO A NEWBORN BABY
By Susan Brink
Imagine yourself in Paris, and you don’t speak French. Pretend for a moment that you’re from rural America, have never seen a big city much less the elegant capitol of France, and you’re trying to cross the Champs-Elysees at the Arc de Triomphe. You dare not step into traffic, you can’t read the street signs, and you cannot understand what people are trying to tell you. Sights and sounds overwhelm you. Nothing makes sense.
That’s something to think about when wondering what the world looks and sounds like to a newborn baby. But there’s more. Dr. Alison Gopnik, professor of psychology at the University of California, Berekley, adds two elements to the confusing mix: love and caffeine. “You want to know what it’s like to be a baby?” says Gopnik. “It’s like being in love for the first time in Paris after four double espressos. It’s fantastic. It’s a wonderful state to be in. And very likely, you’ll wake up at three a.m….crying.”
We look into a newborn baby’s eyes and wonder what he sees. We watch her reactions and wonder what she hears. But now we’ve got a wealth of recent research into what newborns see and hear that adds scientific chops to what parents have been imagining for ages.
Vision
After counting fingers and toes, the first thing most parents do is gaze into their infants’ eyes. We tell ourselves that they’re looking right back. But what, exactly, do they see?
We know that vision is the least developed sense at birth. Babies have heard their mothers’ voices through layers of flesh and organ for nine months already, and they recognize her voice at birth. But they have no similar recognition of her face. Already, they can discern contrast and are drawn to the shadows of eye sockets and the edges of faces. But vision has multiple components, including focus, contrast, coordination between eyes, depth, distance, and color. Their developing brains must lay down dendrites and create synapses between cells in visual areas of the brain, the networks that send and receive signals.
Even as that important brainwork is going on, parts of the eye itself must physically develop. At birth, an infant can project a clear image onto the retina, the light-sensitive tissue at the back of the eye. The images are converted to electric signals and sent on to the brain to interpret. But the fovea, the part of the retina that gives good, detailed vision, is not yet mature. The muscles controlling coordination of binocular vision aren’t yet strong. And the brain architecture that will eventually interpret the signals is not yet up and running. So when a newborn baby looks at an object, the clear image received by the retina falls on a fovea too immature to transmit a clear image to visual areas of the brain. And those visual areas are themselves just beginning to form. In time, the fovea will mature and pass on clear images. And with every visual sensation, the brain adds structure to enable more complete vision.
With every open-eyed observation that passes their way, information is making its way from the eye to the developing visual centers of the brain.
In other words, vision develops through the inevitable practice of looking around.
What Infants See Right Away
Almost from birth, infants are drawn to contrast. We tell ourselves that the baby is looking right into our eyes. If she is, it’s because she notices the contrasting shadow of the eye socket. But it’s equally likely she’s looking at the edge of our face because she’s drawn to the contrast of head against background. For example, newborns can see measurable contrast between very light and very dark objects. At a distance of one foot, they can see high contrast black lines on a white board—lines only 1/16” wide. They notice movement of large, high-contrast objects. In another month, they’ll see some reds and greens. By two months, they’ll be drawn to all the details a loving face, not just the edges and shadows; and they’ll begin to respond to more subtle motions, like the movement of a hand in front of their faces.
There is important visual work going on in the months before a baby actually sees. If the visual pathways, ripe for development early in life, are completely blocked during crucial early periods, the result will be permanent visual impairment. But relax. A healthy baby living within anything resembling a normal human environment will not have those critical pathways blocked.
Research using animal models in the 1960s showed why early visual experience is so important. In experiments done with newborn kittens, scientists sewed shut one eye of each kitten and left it that way for several weeks. When the sutures were removed and the eye allowed to open, the kitten still could not see from that eye, even though the eye was perfectly healthy. What the experiment showed was that if the eye and brain fail to make connections during crucial periods of development, the visual cortex undergoes dramatic reorganization and vision never develops normally.
David Hubel and Torsten Wiesel, Nobel Prize–winning scientists who pioneered this vision work, repeated their work with monkeys. They found that in the normal monkey brain, there are columns of neurons in the visual cortex. Each column receives input from one eye, and the columns alternate between those dominated by information sent from the left eye and those dominated by information from the right eye. The alternating columns allow the brain to start putting that information together as binocular vision.
But among the monkeys deprived of vision in one eye, the neural columns dominated by the seeing eye became wider. The neural columns associated with the blinded eye became narrower. It became clear that in order for monkeys or kittens to see normally, they had to have visual experiences during the earliest weeks of their lives. Without it, the brain’s capacity to make the necessary neural connections was gone.
But the world provides exactly the right visual stimulation for healthy infants without the need of special toys or mobiles. We all have blue sky above, and green trees below and the view of the firmament through branches is a glorious feast of vision. And quite simply, there is nothing an infant likes better than a close-up view of a parent’s face.
It’s a difficult and imprecise business, knowing what a baby is seeing or recognizing. But parents and babies have always gazed into one another’s eyes. It’s deeply rooted, it’s bonding, it’s complex—and it’s important.
Sound
A fire truck screaming, a vacuum cleaner roaring, a talk show host droning, grown-ups chattering, children nattering, dishes clattering. For a newborn baby, the sounds are all there, but the brain isn’t ready to assign more or less importance to any one of them. As a fetus, he heard most of it before, but in utero the sounds were mercifully muffled, almost soothing. The most soothing of all sounds in the new world no doubt is also the most familiar—mother’s voice. Newborns recognize their mothers’ voices, turning toward them more readily than toward any other voices.
Hearing is the most highly developed sense at birth—but newborns cannot yet discern what is worth listening to and what can be safely ignored. They don’t yet have the skill to know where a dog bark ends and a screaming sibling begins, much less to know where one word ends and another begins.
But during the first three months of life, they set about the work, bit by bit, of organizing the sounds around them.
Sorting Through the Din
Think of newborn hearing as a passive exposure with the baby’s brain soaking up sounds and being bathed in the acoustics of his surroundings. Just as each little peek of vision is sculpting new brain circuitry to enable sight, each phrase and sentence sets up the brain wiring that will soon allow the baby to understand where one word ends and another begins. Long before she utters her first “ma-ma” or “da-da,” she’s building the foundation for speech and understanding language.
Babies begin to learn language by listening. And they need to hear human voices. Television and video doesn’t work. That’s because part of what’s needed to learn is human interaction. They learn early on that even their accidental sounds—a burp, a sneeze, a hiccup—get a reaction: a back pat, a gesundheit, a startled look. Soon, another kind of accident happens. The baby leans his head back, the tongue hits the roof of the mouth, and a “g” or “k” sound emerges as he exhales an “oo” sound. It’s a coo! And research tells us that when parents coo back, infants respond by babbling more.
All babies around the world are born with the ability to recognize every sound made in every language on earth. But within months, we lose that ability. The brain is an efficient organ, and just as it’s busy building the connections it will need, it also works at pruning away those neurons that will not be needed.
Dr. Patricia Kuhl, a neuroscientist and professor of speech and hearing at the University of Washington and a leading expert on speech development, discovered why it is that Japanese people have difficulty mastering the ra and la syllables of the English language. Dr. Kuhl and her colleagues tested infants using special pacifiers connected to computers. The infants loved new sounds, and sucked up to eighty times a minute to keep the sound going. But infants, like all of us, get bored with repetition. They eventually slowed down after hearing the same sound over and over. Then as a new sound was introduced, they again sped up their sucking.
Using these special pacifiers, researchers found that infants as young as one month of age heard all sound distinctions— the ones that would become part of their native language, as well as others that they were unlikely to hear as adults. The Japanese babies in the study could tell there was a change in sound when they heard rake and then lake. Japanese adults cannot make the distinction—even the Japanese scientists involved in the experiment couldn’t do it.
When tested at ten months of age, the Japanese babies could no longer make the distinction. If they heard the ra sound long enough to get bored, and then the sound changed to la, they remained bored and inattentive. Whatever inborn ability they had to make the distinction was lost to brains that were preparing themselves for the sounds that would be needed in Japan.
And so it is around the world. A French baby and an American baby have the same ability, for several months, to hear the guttural, rolling r of the French language. Within ten months, the American baby has lost it, and if she tries to learn the French language as a teen or an adult, the unnatural attempt to say rouge or après can be challenging, if not downright embarrassing.
Babies love the sound of voices, the lilt of language. They want it to be interactive. They want to connect facial expressions to words, and every word you utter—for this brief period of time—will be completely fascinating to this listener.
It seems that, once again, nature and biology know what they’re doing in giving sound a head start on vision The world is a confusing enough place to enter with good hearing. It’s probably best that infants are more able to begin understanding sounds as their brains quietly go about the business of developing vision.
Susan Brink is a freelance medical writer. Her book, “The Fourth Trimester: Understanding, Nurturing, and Protecting an Infant Through the First Three Months,” is published by the University of California Press and was released March 20, 2013.
