But when Kuhl put American infants in front of a videotape or audio recording of Mandarin speech, the infants’ brains absorbed none of it. They might as well have heard meaningless noise. This was true despite seeming to be quite engaged by the videos. Kuhl concluded: “The more complex aspects of language, such as phonetics and grammar, are not acquired from TV exposure.”
By implication, we can conclude that baby DVDs don’t delay neural commitment; rather, they have virtually no effect on auditory processing.
The irony here only deepens. One might have noticed that all of these scholars are at the University of Washington. Kuhl and Meltzoff are Co-Directors of the same lab. So when Disney CEO Iger attacked the Pediatrics scholars, he was attacking the very laboratory and institution that Baby Einstein had hailed, when its Language Nursery DVD was first released.
So why does an infant need a live human speaker to learn language from? Why are babies learning nothing from the audio track of a baby DVD, while their language isn’t impaired by exposure to regular TV?
The evidence suggests one factor is that baby DVDs rely on disembodied audio voice-overs, unrelated to the abstract imagery of the video track. Meanwhile, grown-up television shows live actors, usually close up—kids can see their faces as they talk. Studies have repeatedly shown that seeing a person’s face makes a huge difference.
Babies learn to decipher speech partly by lip-reading: they watch how people move their lips and mouths to produce sounds. One of the first things that babies must learn—before they can comprehend any word meanings—is when one word ends and another begins. Without segmentation, an adult’s words probably sound about the same to an infant as does his own babbling. At 7.5 months, babies can segment the speech of people they see speaking. However, if the babies hear speech while looking at an abstract shape, instead of a face, they can’t segment the sounds: the speech once again is just endless gibberish. (Even for adults, seeing someone’s lips as he speaks is the equivalent of a 20-decibel increase in volume.)
When a child sees someone speak and hears his voice, there are two sensory draws—two simultaneous events both telling the child to pay attention to this single object of interest—this moment of human interaction. The result is that the infant is more focused, remembers the event, and learns more. Contrast that to the disconnected voice-overs and images of the baby videos. The sensory inputs don’t build on each other. Instead, they compete.
Would baby DVDs work better if they showed human faces speaking? Possibly. But there’s another reason—a more powerful reason—why language learning can’t be left to DVDs. Video programming can’t interact with the baby, responding to the sounds she makes. Why this is so important requires careful explanation.
Wondering what parents’ prevailing assumptions about language acquisition were, we polled some parents, asking them why they thought one kid picked up language far faster than another. Specifically, we were asking about two typically-developing kids, without hearing or speech impairments.
Most parents admitted they didn’t know, but they had absorbed a little information here and there to inform their guesses. One of these parents was Anne Frazier, mother to ten-month-old Jon and a litigator at a prestigious Chicago law firm; she was working part-time until Jon turned one. Frazier had a Chinese client base and, before having Jon, occasionally traveled to Asia. She’d wanted to learn Mandarin, but her efforts were mostly for naught. She had decided that she was too old—her brain had lost the necessary plasticity—so she was determined to start her son young. When she was dressing or feeding her baby, she had Chinese-language news broadcasts playing on the television in the background. They never sat down just to watch television—she didn’t think that would be good for Jon—but Frazier did try to make sure her child heard twenty minutes of Mandarin a day. She figured it couldn’t hurt.
Frazier also assumed that Jon would prove to have some level of innate verbal ability—but this would be affected by the sheer amount of language Jon was exposed to. Having a general sense that she needed to constantly talk to her child, Frazier was submitting her kid to a veritable barrage of words.
“Nonstop chatter throughout the day,” she affirmed. “As we run errands, or take a walk, I describe what’s on the street—colors, everything I see. It’s very easy for a mother to lose her voice.”
She sounded exhausted describing it. “It’s hard to keep talking to myself all the time,” Frazier confessed. “Infants don’t really contribute anything to the conversation.”
Frazier’s story was similar to many we heard. Parents were vague on the details, but word had gotten out that innate ability wasn’t the only factor: children raised in a more robust, language-intensive home will hit developmental milestones quicker. This is also the premise of popular advice books for parents of newborns, which usually devote a page to reminding parents to talk a lot to their babies, and around their babies. A fast-selling new product being sold to parents is the $699 “verbal pedometer,” a sophisticated gadget the size of a cell phone that can be slipped into the baby’s pocket or car seat. It counts the number of words the baby hears during an hour or day.
The verbal pedometer is actually used by many researchers who study infants’ exposure to language. The inspiration behind such a tool is a famous longitudinal study by Drs. Betty Hart and Todd Risley, from the University of Kansas, published in 1994.
Hart and Risley went into the homes of a variety of families with a seven- to nine-month-old infant. They videotaped an hour of interactions while the parent was feeding the baby or doing chores with the baby nearby—and they repeated this once a month until the children were three. Painstakingly breaking down those tapes into data, Hart and Risley found that infants in welfare families heard about 600 words per hour. Meanwhile, the infants of working-class families heard 900 words per hour, and the infants of professional-class families heard 1,500 words per hour. These gaps only increased when the babies turned into toddlers—not because the parents spoke to their children more often, but because they communicated in more complex sentences, adding to the word count.
This richness of language exposure had a very strong correlation to the children’s resulting vocabulary. By their third birthday, children of professional parents had spoken vocabularies of 1,100 words, on average, while the children of welfare families were less than half as articulate—speaking only 525 words, on average.
The complexity, variety, and sheer amount of language a child hears is certainly one driver of language acquisition. But it’s not scientifically clear that merely hearing lots of language is the crucial, dominant factor. For their part, Hart and Risley wrote pages listing many other variables at play, all of which had correlations with the resulting rate at which the children learned to speak.
In addition, the words in the English language that children hear most often are words like “was,” “of,” “that,” “in,” and “some”—these are termed “closed class” words. Yet children learn these words the most slowly—usually not until after their second birthday. By contrast, children learn nouns first, even though nouns are the least commonly-occurring words in parents’ natural speech to children.
The basic paradigm, that a child’s language output is a direct function of the enormity of input, also doesn’t explain why two children, both of whom have similar home experiences (they might both have highly educated, articulate mothers, for instance) can acquire language on vastly divergent timelines.
A decade ago, Hart and Risley’s work was the cutting edge of language research. It’s still one of the most quoted and cited studies in all of social science. But in the last decade, other scholars have been flying under the radar, teasing out exactly what’s happening in a child’s first two years that pulls her from babble to fluent speech.
If there’s one main lesson from this newest science, it’s this: the basic paradigm has been flipped. The information flow that matters most is in the opposite direction we previously assumed. The centr
al role of the parent is not to push massive amounts of language into the baby’s ears; rather, the central role of the parent is to notice what’s coming from the baby, and respond accordingly—coming from his mouth, his eyes, and his fingers. If, like Anne Frazier, you think a baby isn’t contributing to the conversation, you’ve missed something really important.
In fact, one of the mechanisms helping a baby to talk isn’t a parent’s speech at all—it’s not what a child hears from a parent, but what a parent accomplishes with a well-timed, loving caress.
Dr. Catherine Tamis-LeMonda, of New York University, has spent the last decade looking specifically at parent-responsiveness to infants, and its impact on language development. Along with Dr. Marc Bornstein of the National Institutes of Health, she sent teams of researchers into homes of families with nine-month-old babies. For the most part, these were affluent families with extremely well-educated parents living in the New York City area. The researchers set some age-appropriate toys down on the floor and asked the mother to play with her child for ten minutes.
These interactions were videotaped, and the ten-minute tapes were later broken down second by second. Every time the baby looked to the mother, or babbled, or reached for a toy was noted. The children did this, on average, about 65 times in ten minutes, but some kids were very quiet that day and others very active. Every time the mother responded, immediately, was also noted. The moms might say, “Good job,” or “That’s a spoon,” or “Look here.” The moms responded about 60 percent of the time. Responses that were late, or off-timed (outside a five-second window), were categorized separately.
The researchers then telephoned the mothers every week, for the next year, to track what new words the child was using that week—guided by a checklist of the 680 words and phrases a toddler might know. This created a very accurate record of each child’s progression. (They also repeated the in-home videotape session when the infant was thirteen months old, to get a second scoring of maternal responsiveness.)
On average, the children in Tamis-LeMonda’s study said their first words just before they were thirteen months old. By eighteen months, the average toddler had 50 words in her vocabulary, was combining words together, and was even using language to talk about the recent past. But there was great variability within this sample, with some tots hitting those milestones far earlier, others far later.
The variable that best explained these gaps was how often a mom rapidly responded to her child’s vocalizations and explorations. The toddlers of high-responders were a whopping six months ahead of the toddlers of low-responders. They were saying their first word at ten months, and reaching the other milestones by fourteen months.
Remember, the families in this sample were all well-off, so all the children were exposed to robust parent vocabularies. All the infants heard lots of language. How often a mother initiated a conversation with her child was not predictive of the language outcomes—what mattered was, if the infant initiated, whether the mom responded.
“I couldn’t believe there was that much of a shift in developmental timing,” Tamis-LeMonda recalled. “The shifts were hugely dramatic.” She points to two probable mechanisms to explain it. First, through this call-and-response pattern, the baby’s brain learns that the sounds coming out of his mouth affect his parents and get their attention—that voicing is important, not meaningless. Second, a child needs to associate an object with a word, so the word has to be heard just as an infant is looking at or grabbing it.
In one paper, Tamis-LeMonda compares two little girls in her study, Hannah and Alyssa. At nine months old, both girls could understand about seven words, but weren’t saying any yet. Hannah was vocalizing and exploring only half as often as Alyssa—who did so 100 times during the ten minutes recorded. But Hannah’s mom was significantly more responsive. She missed very few opportunities to respond to Hannah, and described whatever Hannah was looking at twice as often as Alyssa’s mother did with Alyssa. At thirteen months, this gap was confirmed: Hannah’s mom responded 85% of the time, while Alyssa’s mom did so about 55% of the time.
Meanwhile, Hannah was turning into a chatterbox. Alyssa progressed slowly. And the gap only increased month by month. During their eighteenth month, Alyssa added 8 new words to her productive vocabulary, while in that same single-month period, Hannah added a phenomenal 150 words, 50 of which were verbs and adjectives.
At twenty-one months, Alyssa’s most complicated usages were “I pee” and “Mama bye-bye,” while Hannah was using prepositions and gerunds regularly, saying sentences like: “Yoni was eating an onion bagel.” By her second birthday, it was almost impossible to keep track of Hannah’s language, since she could say just about anything.
This variable, how a parent responds to a child’s vocalizations—right in the moment—seems to be the most powerful mechanism pulling a child from babble to fluent speech.
Now, if we take a second look at the famous Hart and Risley study, in light of Tamis-LeMonda’s findings, this same mechanism is apparent. In Hart and Risley’s data, the poor parents initiated conversations just as often with their tots as affluent parents (about once every two minutes). Those initiations were even slightly richer in language than those of the affluent parents. But the real gap was in how parents responded to their children’s actions and speech.
The affluent parents responded to what their child babbled, said, or did over 200 times per hour—a vocal response or a touch of the hand was enough to count. Each time the child spoke or did something, the parent quickly echoed back. The parents on welfare responded to their children’s words and behavior less than half as often, occupied with the burden of chores and larger families. (Subsequent analysis by Dr. Gary Evans showed that parent responsiveness was also dampened by living in crowded homes; crowding leads people to psychologically withdraw, making them less responsive to one another.)
Tamis-LeMonda’s scholarship relies on correlations—on its own, it’s not actually proof that parent-responsiveness causes infants to speed up their language production. To really be convinced that one triggers the other, we’d need controlled experiments where parents increase their response rate, and track if this leads to real-time boosts in infant vocalization.
Luckily, those experiments have been done—by Dr. Michael Goldstein at Cornell University. He gets infants to change how they babble, in just ten minutes flat.
The first time a mother and her infant arrive for an appointment at Michael Goldstein’s lab in the psychology building on the Cornell University campus, they’re not tested at all. They’re simply put in a quiet room with a few toys, for half an hour, to get used to the setting. The walls are white, decorated with Winnie the Pooh stickers. The carpet is light brown and comfortable to sit on. On the floor are many of the same playthings the infant might have at home—a brightly colored stuffed inchworm, stacking rings, a play mat with removable shapes, and a toy chest to explore. At three points around the room, videocameras extend from the wall, draped in white cloth to be inconspicuous. The mom knows full well that she is being watched, both on camera and through a large one-way glass pane. But this is otherwise a nice moment to interact with her baby—she can’t be distracted by the cell phone or household chores. Her baby pulls himself to his mom’s lap, puts the toys nearby in his mouth, and if he can crawl, perhaps pulls himself up to look inside the toy chest.
The next day, mother and baby return. In Goldstein’s seminal experiment, the nine-month-old infant is put in denim overalls that carry a very sensitive wireless microphone in the chest pocket. The mother is given a pair of wireless headphones that still allow her to hear her baby. They are put back in the playroom, and again asked to play together naturally. After ten minutes, a researcher’s voice comes over the headphones with instructions. When the mom hears the prompt “Go ahead,” she’s supposed to lean in even closer to her baby, pat or rub the child, and maybe give him a kiss.
The mom doesn’t know what triggers this cue. The mom just knows t
hat, over the next ten minutes, she hears “Go ahead” a lot, almost six times a minute. She might notice that her baby is vocalizing more—or that he’s waving his arms or flapping his feet—but she won’t know what’s triggering this. For the final ten minutes, she’s asked to simply play and interact naturally with her child again.
When mother and infant leave, she has almost no idea what the researchers might have been up to. For two half-hour periods, she merely played and talked with her child.
But here’s what it was like on the other side of the one-way glass: during those middle ten minutes, every time the child made a voiced sound (as opposed to a cough, grunt, or raspberry), it could be heard loudly over speakers in the observation room. Immediately, the researcher told the mother to “go ahead,” and within a second the mother had affectionately touched the child. Later that night, a graduate student would sit down with the session videotape and take notes, second by second, tracking how often the baby babbled, and what quality of sounds he made.
While all baby babble might sound like gibberish, there’s actually a progression of overlapping stages, with each type of babble more mature and advanced than the one prior. “No less than eighty muscles control the vocal tract, which takes a year or more to gain control of,” Goldstein explained. From birth, children make “quasi-resonant” vowel sounds. They use the back of the vocal tract with a closed throat and little breath support. Because the larynx hasn’t yet descended, what breath there is passes through both the mouth and nose. The result is nasal and creaky, often sounding like the baby is fussy (which it’s not).
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