Learning Language
Language is a critical factor for child development. While babies and toddlers learn a lot about the world from objects, they rarely manipulate objects in total silence. Usually the baby will vocalize and hand objects to adults or to older children.
In play situations, adults naturally name objects for infants and usually provide some extra relevant information as well. Babies learn words most quickly when an adult both points to and names a new item.
Indeed, babies’ brains seem to be primed to learn new words with great rapidity. By the age of 15 months, just hearing a new wordonceis enough for accurate learning. Some studies suggest that 2-year-olds are learning around ten new words every day. This is made possible by the brain’s remarkable facility for language.
Infant-directed Speech
One reason that babies learn language so readily is that we speak to them in a special way. We use infant-directed speech (IDS) orParentese. As noted inChapter 1, IDS appears to be biologically pre-programmed into our species, and is used by adults and children alike.
IDS has a sort of ‘sing-song’ intonation that heightens pitch, exaggerates the length of words, and uses extra stress, exaggerating therhythmicorprosodicaspects of speech. Indeed, sensitivity to speech rhythm has been argued to be a key precursor to language acquisition.
Languages actually differ in theircharacteristic rhythms. Arabic, for example, sounds different rhythmically to French, which is different again to Russian. Experiments based on sucking show that babies as young as 4 days old can discriminate between French and Russian. They seem to do so on the basis of speech rhythm.
The rhythmic or prosodic exaggeration in IDS has a number of important characteristics that support learning. Firstly, the heightened prosody increases the salience of acoustic cues to where wordsbeginandend.
Although we perceive speech as a sequence of words, it is in fact an unbroken stream of sound. We know which bits of the stream are separate words, because we have learned what the words are. We cannot reliably pick out the words in an unknown foreign language.
For example, about 90 per cent of English bisyllabic words for things have a ‘strong-weak’ (or ‘loud-less loud’) rhythmic pattern, like BA-by, BOTT-le, and COOK-ie. In IDS, the first syllable in a strong-weak pattern receives extra stress, emphasizing for the baby that the word beginshere.
Babies learn that this strong-weakstress templatecharacterizes English bisyllabic words. So they begin expecting that word onsets are cued by stressed syllables. Then, if novel words do not fit this pattern, babies mis-segment them. For example, experiments show that 7-month-olds who hear the sentence ‘Her guiTAR is too fancy’ assume that ‘taris’ is a novel word. Ten-month-olds no longer make these mis-segmentation errors.
Another effect of talking in IDS is that it captures attention. Babies like IDS and so they listen to it. Experiments have shown that even newborns prefer IDS over adult-directed speech. Although we also speak more loudly and with exaggerated pitch to people that we assume to be foreign, we do not exaggerate prosody in the same way.
Similarly, although we appear to speak to pets in IDS, close analysis of the acoustic characteristics of so-called ‘pet-ese’ show that it is quite different to IDS.
Pet-directed speech does not include the exaggerated prosodic contours found in IDS, and it does not include hyper-articulated vowels. So as well as capturingattention, IDS is emphasizingkey linguistic cuesthat help language acquisition.
Finally, IDS marks information that is new. In one study, mothers read a picture book to their babies, and researchers measured which words received the most stress. New words received primary stress on 76 per cent of occasions.
When new words were read for the second time, they were again highly stressed on 70 per cent of occasions. When the mothers were reading the same book to another adult, this did not occur.
Across cultures, similar effects are found. Mothers and other carers are not aware that they are using IDS to teach babies new information, but they are.
