Language development

Human infants are acutely attuned to the human voice and prefer it above allother sounds. In fact, they prefer the higher pitch ranges characteristic offemale voices. They are also attentive to the human face, particularly the eyes, which they stare at even more if the face is talking. These preferences are present at birth, and some research indicates that babies even listen to their mother's voice during the last few months of pregnancy.

Since the early 1970s, it has been known that babies can detect very subtle differences between English phonemes (the functional units of speech sound). For example, they can detect the difference between "pa" and "ba," or between"da" and "ga." Of course, they do not attach meaning to the differences for 12 months or more.

At the beginning of infancy, vegetative noises and crying predominate. Observers note that by the age of four months, the baby's repertoire has expanded in more interesting ways. By this point babies are smiling at caregivers and making cooing and gurgling noises that are irresistible to most parents. It iscommon for the caregiver to respond by echoing these noises, thereby creating an elaborate interchange that can last many minutes.

At some point between four and 10 months, the infant begins producing more speech-like syllables, with a full resonant vowel and an appropriate "closure"of the stream of sound, approaching a true consonant. This stage is called "canonical babbling."

At about six to eight months, the range of vocalizations grows dramatically.Not all of these are human phonemes, and not all of them are found in the language around them. Research has shown that Japanese and American infants sound alike at this stage, and even congenitally deaf infants babble, though lessfrequently. These facts suggest that the infant is "exercising" her speech organs but is not being guided very much, if at all, by what she has heard.

By age 10 or 12 months, however, the range of sounds being produced has somewhat narrowed, and now babies' babbling in different cultures begin to take onsound characteristics of the language that surrounds them. The babbling at this stage often consists of repeated syllables like "bababa" or "dadada" or "mamama." It is no accident that most of the world's languages have chosen some variant of "papa," "mama," "dada," and "nana" as names for parents.

The first words make their appearance any time between 9 and 15 months or so,depending on the child's precocity and the parent's enthusiasm in noticing.What the baby "means" by these sounds is questionable at first. But before long the baby uses the sounds to draw a caregiver's attention, and persists until she gets it, or uses a sound to demand an object, and persists until it isgiven to her. There is a fairly protracted period for most babies in which their first words come and go, as if there is a "word of the week." After several months of slow growth, there is an explosion of new words, often called the "word spurt." This usually coincides with an interest in what things are called. Vocabulary climbs precipitously from then on, with an estimated nine new words a day from ages two to 18 years. These developments are noted in allthe cultures that have been studied to date.

The nature of the child's first 50 words is quite similar across cultures: the child often names foods, pets, animals, family members, toys, vehicles, andclothing that the child can manipulate; she generally omits words for furniture, geographical features, buildings, weather, and so forth. Researchers agree that the child learns most effectively from social and interactive routines with an accomplished talker (who may be an older child), and not, at leastat the start, from passive observations of adults talking or from radio or TVshows. Experiments and observations show that children pick up words at thisstage most rapidly when the caregiver uses them to name or comment on what the child is already focused on.

The meanings of the child's first words are not necessarily the same as thoseof the adults around her. For instance, children may "overgeneralize" theirfirst words to refer to items beyond their usual scope of application. A child might call all men "Daddy," or all animals "doggie," or all round objects "ball." Others have pointed out that "undergeneralization" also occurs, thoughit is less likely to be noticed. For instance, a child might call only her own striped ball "ball," and stay silent about all the rest, or refer to the family dog and others of the same type as "doggie" but not name any others. The child may also use a word to refer to a wide variety of objects that hold no single property in common except a shifting form of resemblance to the named object. It has been argued that children's first word meanings have only afamily resemblance rather than a common thread. In fact, there are philosophers who argue that such is the nature of many adult words as well.

Most toddlers produce their first spontaneous two-word sentence at 18 to 24 months, usually once they have acquired between 50 and 500 words. At the start, the child combines the single words into two-word strings that usually preserve the common order of parents' sentences in English. At the time the English-speaking child is producing many two-word utterances, comprehension testsshow he can also distinguish between sentences that contrast in word order and hence meaning:

The dog licks the cat

The cat licks the dog.

Most studies on early child language conclude that the child at the two-wordstage is concerned with the expression of a small set of semantic relationships. All over the world, children apparently talk about the same meanings or ideas in their first sentences, despite the variety of forms in those languages. For example, the children refer to possession (Mommy dish, my coat), action-object sequences (hit ball, drop fork), attribute of an object (big truck,wet pants), or an object's location (cup shelf, teddy bed).

In the next stage of development of English, the extra little function wordsand inflections that modulate the meaning of the major syntactic relations make their appearance, though it is years until they are fully mastered. A classic error noticed in the acquisition of English inflections is the overgeneralization of plurals and past tenses. In each case, when the regular inflection begins to be mastered, it is overgeneralized to irregular forms, resultingin errors like foots, sheeps, goed, and eated. Two kinds of overgeneralizations occur: one in which the -ed ending is attached to the root form of the irregular verb (e.g. sing/singed) and the other in which the ending is attachedto the irregular past form (e.g. broke/broked).

Children's first sentences lack any auxiliaries or tense markers: "Me go home"; "Daddy have tea." They also lack auxiliary-inversion for questions at thisstage: "I ride train?" "Sit chair?"

They also lack a system for assigning nominative case to the subject, that is, adult sentences mark the subject as nominative: "I want that book"; but children at this stage frequently use the accusative case: "Me want that book."

In addition to learning the basic word order and inflectional system of the language, a child must learn how to produce sentences of different kinds: notjust simple active declarative, but also negatives, questions, imperatives, passives, and so forth. In English there are word order changes and auxiliarychanges for these sentence modalities.

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