Language Development

Language development in humans begins even before birth. Research results have shown that babies listen to their mother's voice while in the womb during the last few months of pregnancy and may also hear other sounds from outside the mother's body. Babies whose mothers read to them while in the womb also show the ability to pick out their mother's voice from among other female voices. Human infants are acutely attuned to the human voice and, from birth, prefer it above all other sounds. In fact, they prefer the higher pitch ranges characteristic of female voices. They are also attentive to the human face and may stare at the eyes of someone who is talking.

Babies have finely tuned perception when it comes to speech sounds, and, more importantly, they seem to classify many sounds in the same way as adult speakers, a phenomenon known as categorical perception. Sounds they perceive as indivisible categories are generally those that form the basis for many speech systems in the world's languages, rather than those that are used only rarely, like th. Infants come into the world already predisposed to make certain distinctions and classifications, and apparently they are not driven to make them by language exposure. Babies in English-speaking countries have demonstrated the ability to detect extremely 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. However, babies do not attach meaning to the differences for 12 months or more.

In early 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, including smiling at caregivers and expressing cooing noises. When the baby is being fed or changed, the baby will frequently lock gazes with the caregiver and coo in a pleasant way, often gurgling and making noises that sound like hi. Caregivers may respond by echoing these noises, thereby creating an elaborate interchange that can last many minutes. This is a very early form of dyadic communication. This may not happen universally, however, as not all cultures take the baby's vocalization seriously. The nature of the sounds made at this stage is not fully speech-like, though there are open-mouth noises like vowels, and an occasional closure akin to a consonant, but without the full properties that normally make a syllable out of the two.

At some point between four and ten months, infants typically begin 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, and babies can spend hours practicing the sounds they can make with their mouths. Not all of these are human phonemes, and not all of them are found in the language around the baby. Research has shown that Japanese and American infants sound alike at this stage, and even congenitally deaf infants babble, though less frequently. These facts suggest that infants exercise their speech organs but are not guided very much, if at all, by what they have heard.

By age 10 or 12 months, the range of sounds a child makes narrows somewhat, and now babies’ babbling in different cultures begin to take on sound characteristics of the language that surrounds them. The babbling at this stage often consists of reduplicated syllables like bababa or dadada or mamama. It is no accident that most of the world's languages have chosen, as names for parents, some variant of papa, mama, dada, or nana. These coincide with articulations that baby can make most easily at the end of the first year.

The first words make their appearance any time between nine and 15 months or so, depending on the child's precocity and the parent's enthusiasm in noticing. That is, the baby begins making sounds that occur fairly reliably in some situations and are at least a vague approximation to an adult-sounding word.

The nature of the child's first 50 words is quite similar across cultures, including naming foods, pets, animals, family members, toys, vehicles, and clothing items that the child can manipulate. Most of what is named can either move or be moved by the child: the child generally omits words for furniture, geographical features, buildings, weather, and so forth. Some children develop an early vocabulary almost exclusively of object words and actions, whereas others develop a social language: words for social routines, and expressions of love and greetings. Researchers do not agree as to whether these are different styles inherent in the child or whether the child's social environment encourages the child in different ways. However, researchers agree that children learn most effectively from social and interactive routines with an accomplished talker (an older child, a parent, or other adult), and not, at least at the start, from passive observations of adults talking or from radio or TV shows. Experiments and observations show that children pick up words most rapidly at this stage when the caregiver uses them to name or comment on what the child is already focused on and when this occurs frequently.

The meanings of the child's first words are not necessarily the same as those of the adults around the child. For instance, children may overgeneralize their first 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, though it 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. A child who learned moon for the full moon may later use it for street lamps, house lights (lights in common), doorknobs and the dial on the dishwasher (shape in common), and toenail clippings on a rug (related shape). Put into a class, these objects share nothing in common except a shifting form of resemblance to the original subject, the Moon. It has been argued that children's first word meanings have only a family resemblance rather than a common thread. In fact, there are philosophers who argue that such is the nature of many adult words as well.

It has long been recognized that words are inherently ambiguous even when an object is being pointed at: does the word refer to the object or its color, shape, texture, function, shadow? Some work on word learning has also drawn attention to the biases the child brings to word learning. One such bias is the whole-object assumption, that is, children assume a new word refers to the object itself rather than a property. However, a competing constraint is mutual exclusivity: if a child already knows a word for an object, a new word is assumed to mean something else; a new object if it is available; or a part, texture, or shape of a known one. Researchers are divided on the extent to which these biases are learned or inherent.

The first sentence is the transition that separates humans from other creatures. Most toddlers produce their first spontaneous two-word sentence at 18 to 24 months, usually once they have acquired between 50 and 500 words. Before their first sentence, they often achieve the effect of complex expressions by stringing together their simple words:

The next step toward a first sentence puts these words under a single intonational envelope, with no pause. These first sentences are not profound, but they represent a major advance in the expression of meaning. The listener is freed from some of the burden of interpretation and does not need to guess so much from context.

For children learning English, their first sentences are telegraphic, that is, content words predominate, primarily the nouns and verbs necessary in the situation. Words that have grammatical functions, but do not themselves make reference, such as articles, prepositions and auxiliary verbs, are not often used. The true character of this grammar is hotly debated. The fact that the function words and inflections appear variably for a protracted period of months leads some researchers to argue that the child really knows the grammar but has some kind of production limit that precludes saying extra words. On the other side, some researchers argue that the forms that do appear to be imitations, or particular learned fragments, and that the full grammar is not yet present. Tests of comprehension or judgment that might decide between these alternatives are difficult to undertake with two-year-old children, although the few studies that do exist suggest that children are sensitive to items they omit in their own speech.

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 expressing two-word communication, comprehension tests show he can also distinguish between sentences longer than two words that contrast in word order and thus in meaning:

Researchers using innovative techniques with preverbal infants have reported that infants understand basic word order contrasts before they learn to produce them. Infants who saw a choice of two brief movies along with spoken sentences preferred to look at the movie of the event that was congruent with the spoken sentence, where the only contrast was in word order.

Most studies on early child language development conclude that children at the two-word stage are concerned with the expression of a small set of semantic relationships. The cross-linguistic study of children includes languages as remotely related as French, Samoan, Luo (spoken in Kenya), German, Finnish, and Cakchiquel (a Mayan language spoken in Guatemala). Two-year-old children learning all these languages expressed only a narrow range of the possible meanings that the adult language could express. Apparently children worldwide talk about the same meanings—or ideas—in their first sentences, despite the variety of forms in those languages. For example, children refer to possession (Mommy dish, my coat), action-object sequences (hit ball, drop fork), attributes of an object (big truck, wet pants) or an object's location (cup shelf, teddy bed).

Debate continues over how significant this finding of universal semantic relationships may be for the study of grammatical development. For instance, it may mean that building a grammar based on meaningful relationships is a universal first step for language learning. However, the larger problem is how the child builds a grammar that resembles that of the adult, because for true linguistic competence, the child needs to assemble the right language components, including subjects, objects, noun phrases, verb phrases, and the rest. These abstract categories do not translate easily into semantic relationships, if at all. To succeed at analyzing adult sentences into their true grammatical parts, the child must go beyond general meaning. Interpretation of the findings surrounding first sentences indicates that children all over the world are constrained by individual cognitive development to talk about the same ideas and that their grammars may not be based solely on semantic relationships. Therefore, the semantic analysis of children's early sentences offers fascinating data on the meanings children express at the first-sentence stage, but these semantic notions may or may not be the components from which children's grammars are constructed.

What is missing from the two-word stage are the modulations of meaning, the fine tunings, which add immeasurably to the subtlety of what humans can express. Consider the shades of meaning in the following sentences:

An understanding of how children acquire grammatical morphemes is thought to require a broader perspective than that obtained from studying English alone. Data gathered from children acquiring other languages, especially languages very different from English (e.g., Luo, Samoan, Kaluli, Hungarian, Sesotho) suggest that the telegraphic speech style of native English-speaking children is not universal, especially in more heavily inflected languages such as Italian, in which even the youngest speakers do not strip their sentences to component parts such as nouns and verbs. English-speaking children also acquire the hypothetical (if/then statements) rather late, around four years of age, but the hypothetical form is complex in English grammar, requiring an ability to imagine an unreal situation. Research shows that Russian children do not use this simple hypothetical form until after they are about four years of age. Most morphemes vary along multiple dimensions: phonological, semantic, and grammatical. Researchers are able to study the massive matrix of possibilities across the world's languages using detailed longitudinal data from children learning those languages.

In addition to learning the basic word order and inflectional system of the surrounding language, a child must learn how to produce sentences of different kinds: not just simple active declarative, but also negatives, questions, imperatives, passives, and so forth. In English, word order changes and auxiliary changes are associated with these sentence modalities. For example, one type of question is called a yes/no question, for the simple reason that it requires a yes or a no answer. A second kind of question is called the Wh-question because it usually begins with the sequence Wh in English using “What, who, when, where, why and how” (in French, they are Qu-questions). Wh-questions do not require a simple yes or no response: instead they ask for information about one of the constituents in the sentence. Children's responses to such questions reveal the sophisticated nature of their grammatical knowledge. Auxiliaries appear to emerge first in declarative sentences. Before children master the placement of the auxiliary, they ask questions using rising intonation. They may also pick up a few routine forms of yes/no questions, particularly in households that demand politeness from young children, as in the following:

Modern linguistic theory holds that, when auxiliaries do begin to appear in initial position, the rules of natural languages are structure dependent, always referring to structural units such as noun phrase or auxiliary verb.

Wh-questions appear among the child's first utterances, often in a form such as “Whazzat?” The first, stereotypical forms may be tied to particular functions or contexts, but genuine interrogatives vary not only in form but in use. Just as in yes/no questions, the auxiliary must be in front of the subject noun phrase in a Wh-question, and children seem to have more difficulty with auxiliary-inversion in Wh-questions than in yes/no questions. Children must learn the link between the Wh-word and the missing constituent. Studies have shown that certain Wh-words enter children's speech earlier than others: What, who, and where tend to emerge before why and how, with when coming later. Some have explained the order in terms of semantics, or concreteness of the ideas contained in these words, since when and how depend upon cognitive development of time and causality whereas what and who do not. The question why seems to be late for this reason: It is only through discourse that a child can determine the meaning of why, which may explain why some young children ask it endlessly.

Once children have mastered the fundamentals of sentence construction, they begin to expand the length and complexity of sentences. This varies between children, again based on cognitive development, and can progress slowly over a long period of time. The mean length of utterances of children younger than age four tends to be unimpressive, ranging only from 1.0 to 4.0 morphemes per utterance. Yet by age four, the MLU (mean length of utterance) loses much of its usefulness as a measure, because children's utterances, like those of an adult, fluctuate in length dramatically depending on the circumstances of the conversation. Even before age four, children may utter sentences of rare, but significant, complexity, showing that the child is in command of a considerable amount of grammar when needed. The first sentences involving more than one proposition are simple coordinations, for instance two sentences joined by and. Later other conjunctions come in, such as so, but, or and because. But embeddings arrive not much later: embedded structures (relative clauses modifying a noun phrase, or constructions modifying verb phrases) may show up even in the primitive talk of two-year-olds. Both types of embedding are means of packing information into a single sentence that would require multiple sentences (probably with lots of pointing) to convey equivalent ideas. When children reach the stage at which they can control these and similar structures, they become capable of expressing a much wider variety of ideas and thoughts not dependent on the immediate environment for support, and an important further step is taken in being ready for literacy.

The child's vocabulary grows enormously between ages two to five years, and vocabulary size is frequently used by researchers as an index of the child's development. In addition to learning many new nouns and verbs, the child must organize vocabulary, for example, into hierarchies: that Rover is also a dog, a corgi, an animal, a living thing and so on. The child also learns about opposites and relatedness—all necessary forms of connection among words in the inner lexicon. The child also becomes better able to learn words from linguistic context alone, rapidly homing in on the meaning after only a few scattered exposures. This is a surprisingly effective process, though hardly fail-safe: after being told that screens are to stop flies from bringing germs into the house, one child concluded that germs are “things flies play with.”

Children's language learning does not take place in a vacuum or a laboratory; it is enmeshed in the social relationships and circumstances of the child. The child uses language for communication with peers, siblings, parents, and strangers, all of whom may make special demands on the child in terms of different statuses, knowledge, requirements for politeness, clarity or formality. In response, the child must adjust and adapt, and the preschool child is only beginning this process of language socialization. Even four-year-olds adjust their style, pitch, and sentence length when talking to younger children or infants rather than peers or older people, and in other cultures they master formal devices that acknowledge the status or group membership of different people. However, three-year-olds are rather poor at predicting what others know or think and, therefore, may be rather egocentric in expressing themselves. However, children become increasingly adept at repairing their own communicative breakdowns as they get older.

Advances in voice, speech, and language research have focused mainly on speech and language disorders, including the discovery and confirmation of a genetic basis of speech and language disorders such as stuttering, rather than attributing these to behavior only. Distinct language phenotypes have also been identified that may be useful in conjunction with further genetic studies, helping to investigate the genetic, neurologic, and other causal factors associated with language impairment. Such discoveries are expected to expand the classification, diagnosis, and treatment of language, reading, and speech disorders. At the same time, evidence is growing for the involvement of various cognitive processes in language processing, including short-term memory, attention, and executive functions. Brain development from infancy through adolescence continues to be investigated and characterized in longitudinal studies, providing information on the neural, muscular, and anatomic factors behind language development and speech.

See also Child development ; Specific language impairment (SLI).