Whether you think it's cute, or it makes you squirm, baby talk is a compelling scientific phenomenon. All around the world, people use a special register when they speak to the very young. This "infant-directed speech," or IDS, is recognizable for its higher pitch and more melodic, emotionally-charged tone.
These features capture a baby's attention, and make it easier for her to grasp the emotional intentions of speech.
In fact, fascinating experiments show that adults listening to a foreign language are better able to pick up on a speaker's emotions when he uses infant-directed speech. You can read more about it in my article on the attention-getting and emotional functions of baby talk.
But what about language development? Does infant-directed speech help babies learn how to talk? Infant-directed speech includes many modifications that seem tailor-made for the language learner:
It’s slower, more repetitive, and more likely to exaggerate the pronunciation of vowels. In addition, people using IDS are more likely speak in shorter, simpler utterances. Experiments suggest that these modifications help babies develop several key abilities, including
It's even possible that individual differences in the way that parents use baby talk could affect how quickly infants learn to speak.
So it seems that we have lots of reasons to forget our inhibitions and let loose with the baby talk. Here is the evidence.
When people use IDS, they may hyper-articulate, or "stretch out," the pronunciation of vowel sounds. Adults do the same thing when they talk to people with foreign accents (Uther et al 2007).
Does this exaggerated pronunciation make it easier for people to learn about speech sounds? If so, we might predict that the more a mother hyper-articulates, the better her infant should perform on tests of speech perception.
Researchers Huei-Mei Liu and colleagues tested this idea by performing an experiment on Mandarin-speaking mother-infant pairs in Taiwan (Lui et al 2003).
The infants (aged 6 to 12 months) were presented with a background sound—a Mandarin Chinese word repeated over and over again on a loudspeaker. Then researchers switched to another word, one that differed by a single consonant (like switching from "jet" to "set"). If babies recognized the switch, they turned their heads toward the loudspeaker.
Using this measure, the researchers assessed each baby’s speech perception skills in a series of 30 trials. They also recorded and analyzed the infant-directed speech patterns of the baby’s mother.
The results? There was a strong correlation between maternal baby talk and baby speech perception skills.
Moms who tended to "stretch out" their vowels had babies who performed better on the speech perception test.
And the link remained significant even after the researchers controlled for socioeconomic variables, like parental education level and occupation.
This doesn’t prove that infant-directed speech helps babies learn speech sounds. It’s possible that some unidentified factor--like an inherited aptitude for both speaking and perceiving speech sounds--explains the link between maternal speech clarity and infant speech perception.
Moreover, it's not clear how many people actually do hyper-articulate when they address babies. A recent experiment in Japan found that mothers had a slight tendency to enunciate less clearly when speaking to their infants (Martin et al 2015).
But other research supports the notion that hyper-articulated baby talk helps listeners "tune into" the right speech sounds.
One experiment using playbacks of computer-synthesized speech found that infants under 4 months of age could detect a change in the 2nd syllable of a 3-syllable utterance only when the 2nd syllable was spoken in speech that simulated the high pitch, intensity, and stretched-out pronunciation of baby talk (Karzon 1985).
And researchers have used a computer model to test if baby talk makes vowel sounds easier to learn. Bart deBoer and Patricia Kuhl presented the computer model with samples of adult-directed and infant-directed speech, then "asked" the model to identify certain key vowel sounds. When the computer model was exposed only to baby talk, its answers were more accurate (deBoer and Kuhl 2003).
Baby talk may make it easier to hear the sounds of speech. But how do babies figure out which sounds make up a word?
It’s a problem for any language learner. When adults talk to each other, their rapid-fire, often ungrammatical speech is difficult for a non-native speaker to parse. Words run together. It’s hard to tell where one word ends and another begins.
For instance, consider the phrase “Mama is happy.” When it’s spoken, it sounds like “mamaizhappy.” Where are the boundaries between words? To a person who doesn’t know English, there are many possibilities, like:
"Ma ma izhapp y"
"Mamaiz ha ppy"
"Ma ma izhappy"
So how do listeners find the right word boundaries?
One answer is that the listener hears lots of utterances and eventually their brains notice statistical patterns. She notices, for instance, that the sounds “iz happ” get paired up less often that “hap pee.” So she figures out that “happy” is a word and “izhapp” is not (Saffron et al 1996).
8-month old babies can do this by listening to many examples of adult-directed speech (Saffron et al 1996). But it seems to be difficult.
An experiment on slightly younger babies (6.5 to 7.5 months old) suggests that word segmentation is much easier when babies have been listening to infant-directed speech (Thiessen et al 2005).
Moreover, baby talk seems to help adults, too. When English-speaking adults were presented with playbacks of Mandarin Chinese, they were able to pick out and learn new words more easily when the playbacks featured infant-directed speech (Golinkoff and Alioto 1995).
It seems, then, that infant-directed speech has properties that make it easier for listeners find the boundaries between words (Kemler-Nelson et al 1989; Thiessen et al 2005). But what are these?
To some degree, baby talk helps because it's an attention-grabber.
A variety of experiments demonstrate that babies prefer listening to infant-directed speech. And when babies pay more attention, they may be more likely to notice the statistical patterns in speech. Enhanced attention may also help them remember these patterns better (Thiessen et al 2005).
Consistent with this idea, researchers report that infant-directed speech--accompanied by direct eye contact--has a special effect on the brain.
When adults communicated face-to-face using infant-directed
speech, babies experience enhanced activity in brain regions associated
with processing auditory messages. Similar attempts using everyday,
adult speech had no such effect (Lloyd-Fox et al 2015).
But infant-directed speech does more than perk a baby's interest. People using IDS tend to repeat their words, giving babies extra opportunities to listen and learn.
When researchers tracked the development of 121 infants, they found that a mother's tendency to use repetitive language at 7 months predicted her child's vocabulary at 24 months (Newman et al 2015).
In addition, IDS is structured in ways that make it objectively easier to segment speech into words. Infant-directed speech is slower and marks the spaces between phrases with longer pauses (Kuhl et al 1997). And speakers sometimes make key words stand out.
For example, in English-speaking countries, adults addressing babies tend to alter their typical sentence structure, re-ordering things so that a new or important word comes at the end of an utterance (Fernald and Mazzie 1991; Aslin et al 1996).
People do the same thing when they are teaching adults new, technical terms (Fernald and Mazzie 1991), and it’s a helpful ploy: In one study, 15-month-old infants were better able to recognize new words when these words appeared in the final position of an utterance (Fernald et al 1998).
As noted above, that's hard to prove on the basis of simple correlations between parents and babies. Parents who are really good at IDS might be good at language in general. We can't rule out the possibility that genetics plays a role in their children's development.
But the experiments we've considered show that infant-directed speech helps listeners notice key features of speech in the short-term. It makes sense to think these features have a lasting, ongoing impact.
Moreover, we've reason to think that the expressiveness of our language helps capture a baby's attention, a crucial prerequisite for learning.
In one experiment on 4-month-old infants, Peter Kaplan and his colleagues found that babies could learn to associate a photograph of an unfamiliar, smiling face with an unfamiliar voice speaking baby talk (Kaplan et al 2002). But there was a catch:
When the speaker was a depressed woman, her infant-directed speech was flatter, more monotonic, and the babies failed to show significant learning in the task.
Peter Kaplan and his colleagues conducted similar experiments more recently, and have found disturbing links to postpartum depression.
When they tested babies twice -- at 4 months and 12 months -- they found that maternal depression at 4 months postpartum predicted later learning trouble: 12-month-old babies failed to learn the new face-voice association, even if their mothers' mental health had improved (Kaplan et al 2012).
So it seems that the quality of infant-directed speech can have an impact on the way babies learn, and that early exposure matters. Women suffering from postpartum depression have yet another reason to seek treatment and support.
It’s also possible that the absence of expressive baby talk may contribute to speech delays in some toddlers. Studies suggest that some "late talkers"--defined as toddlers who reach the age of 2 years with fewer than 50 words in their vocabularies--haven’t heard as much expressive infant-directed speech as have normally-developing kids.
In particular, researchers have found that mothers of late talkers speak target words with a lower pitch than do mothers of normally-developing kids (D'Odorico and Jacob 2006; Hampson and Nelson 1993).
Of course, we should be careful interpreting such studies. Just because you have a late talker doesn’t mean you failed to provide your baby with the right kind of baby talk!
But it seems there is ample evidence to show that infant-directed speech is helpful. I think we might consider it an important facet of responsive, sensitive parenting during the first two years of life.
For more information about the ways that young children learn speech, see my articles about the effects of television on children's language skills and baby sign language.
In addition, you can read more about the attention-getting and emotional functions of infant-directed speech here.
And check out your baby's ability to "mind meld." Read my article, "Talking to babies: How friendly eye contact can help babies tune in -- and mirror your brain waves."
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Content last modified 10/2015
image of man with baby cropped from photograph by Toshimasa Ishibashi/flickr
image of baby boy by Ludmila27/wikimedia commons
closeup of mother and infant by Daniel Moustapha / wikimedia commons
image of mother talking to baby by Steve Hildebrand / US Fish and Wildlife