Are you ever embarrassed when you hear an adult talking "baby talk" to a baby? Do you ever think, or even say, that no baby could learn to talk sensibly after hearing that goofy high-pitched jabber? If you have felt that way, I guess nobody ever told you that hearing baby talk is the best way for babies to learn about their parents' language.
Yes, it's true, baby talking adults are giving some excellent instruction that helps infants move toward childish, then adult, language abilities. Keep in mind here that I'm talking about babies, not about preschoolers or older children, who are learning their own language skills, quite differently from the way the very young do it.
In my last post, I referred to the work of Andrew Meltzoff and discussed his emphasis on social behavior and motivation as the basis of learning. In his "Science" article (Meltzoff, A.N., Kuhl, P.K., Movellan, J., & Sejnowski, T.J. (2009). Foundations for a new science of learning. Vol. 325, pp. 284-288), Meltzoff commented on the tendency of infants to follow the gaze of adults, to pay attention to what adults look at, and thus to have their learning guided by older members of their community.
Baby talk also works in co-operation with infants' social skills and interests. Sometimes described as "motherese" or "parentese" or "infant-directed talk", baby talk presents infants with some fascinating stimulus characteristics. Baby talk in all languages is higher in pitch (perceived sound frequency) than adult-directed speech, and babies are especially attentive to high pitches. Baby talk also has a very predictable and pronounced rhythm which catches babies' attention. And, baby talk is accompanied by adult eye contact and gaze movement, by exaggerated facial expressions, by rhythmic movement and gesture-- by a whole panoply of stimuli, all linked to each other and all of great interest to human infants.
We can see that babies are likely to pay more attention to baby talk than they do to "normal" adult-directed speech. So, they are likely to learn, just because they are paying attention. But what exactly do babies learn when they listen to baby talk? Do they learn silly made-up words that they will have to correct later on?
Babies who are learning from baby talk are not ready to learn words yet. They are still learning the phonemes or basic speech sounds of their parents' language. Because different languages may use different phonemes, and because humans can make many different sounds with their mouths, babies have to learn which mouth noises are part of speech, and which ones are sneezes, hiccups, or a parent pretending to be a cow.
Babies learn phonemes by using their computational skills, as Meltzoff points out. They are able to put together hundreds and thousands of "mouth sound" experiences and to extract from them reliable information about their native language's phonemes--- doing this without intention or awareness, of course. As they get a little older, they will use the same computational skills when they mentally divide a stream of speech into the separate words that make it up, a task that they can do even when there are no pauses between the spoken words.
Presumably, babies could learn their language's phonemes by listening to adult-directed speech as well as by listening to baby talk. The thing is, they are not very interested in adult-directed speech. ADT, as it is abbreviated, is lower-pitched than babies like. It is not very rhythmic or repetitious, and it does not include the differences in emphasis characteristic of infant-directed speech (IDT). In addition, when adults talk to other adults, they do not use the emphatic eye movements, facial expressions, and gestures that are linked with IDT. Bo-ring, the babies say, and they stop paying attention, until someone speaks directly to them in the ways they prefer. So, although babies could learn from the kinds of words adults say to each other, they generally do not, because they aren't interested.
Even when babies know their phonemes and are getting to know some words, after about 6 months of age, baby talk still gives them some advantages. IDT uses short sentences and simple concepts, but it is grammatically much more predictable than ADT. When we talk to another adult, we know we can say " Hey, there's that--- you know, that--- that----", and an adult easily guesses that we mean the bird we were discussing 15 minutes before. In talking to babies, adults make sure that they say the right words, and in fact repeat and emphasize them in ways never used with other adults.
Few people need to worry that they will talk baby talk longer than their children need it. As children show us their growing attentiveness to speech and understanding of language, we automatically shift our style to jibe with their abilities. It's one of those things that, as Dr. Spock said, we understand better than we know.