Early Language Development - Appunti

Context-bound words become decontextualised

The description of the beginning of lexical development that emerges from studies of this early stage is one in which children start out with at least two kinds of lexical entries for the words they use:

• One kind of lexical entry is situation specific: this is a word you can say in this particular circumstance.
• The other kind of lexical entry is more adult-like: this is a word that encodes this meaning, and you can say it whenever you wish to express this meaning.

Although some words enter the lexicon as context-bound words and gradually become decontextualised, other words are contextually flexible from the time the child first uses them.

Vocabulary development from first words to 50 words

For several months after the appearance of their first words, most children add words to their vocabulary slowly at first but with increasing speed as they approach the achievement of a 50-word vocabulary.

18 months of age (but ranging from 15 to 24 months): children achieve a productive vocabulary of 50 words.

The results of Katharine Nelson’s (1973) longitudinal study of 18 children can be used to illustrate the course of lexical development from children’s first words to the 50-word vocabulary mark. Each mother in Nelson’s study kept a diary and recorded each new word her child produced, along with the date and notes about the context in which the word was used. The mothers kept recordings until their children had acquired 50 words. From these records, Nelson was able to analyse the content of children’s 50-word vocabularies and the course of their lexical development to that point.

Nelson classified the children’s words into 6 different categories:

• Specific nominals, such as Mommy, Daddy, Rover
• General nominals, including common nouns such as dog, ball, milk, and pronouns like he, this
• Action words, such as go, up, look
• Modifiers, such as big, all gone, outside, mine
• Personal social words, such as no, want, please
• Grammatical function words, such as what, is, for

Nominals (general and specific) were the larger single category of children’s words, from the first 10 words to the 50-word mark. She also found that the proportion of general nominals in children’s vocabularies increased as vocabulary size increased during this period.

The content of children’s 50-word vocabularies

The vocabularies of very young children are not just small versions of the vocabularies of older children and adults; they differ in the kinds of words they contain. Children’s first words reflect their experiences. They know names for people, food, body parts, clothing, animals, and household items that are involved in children’s daily routines. Routines are also the source of early expressions such as night-night and bye-bye.

First verbs include labels for actions that are part of children’s routines (e.g., eat, drink, kiss, sing) and verbs with more general meanings that are frequent in children’s input (e.g., look, go, come, do). One feature of early vocabularies that has received a great deal of attention is the predominance of nouns. For English-speaking children with vocabularies between 20 and 50 words, fully 45% of their vocabulary consists of nouns, compared with 3% for verbs.

What determines the content of early vocabularies?

Children acquire nouns before verbs. The meanings nouns encode are easier for children to learn than are the meanings verbs encode. Nouns refer to entities or things (like tables, chairs, birds, or dogs) and young children can have an understanding of things based on their perception of the physical world. Children acquiring Korean, Japanese, and Mandarin show less of a noun bias than do children acquiring English.

In these languages, a verb is often the final word in a sentence, and this position may be particularly salient to children. Also, the grammars of these languages allow noun dropping, thus making verbs relatively more frequent in the input. The culture in which a language is used also shapes input and affects children’s vocabulary development. American mothers - at least the middle-class mothers, most frequently studied - spend a great deal of time labelling objects for their babies.

Overextensions and underextensions of first words

Sometimes children may use words in a more restricted fashion, such as using dog to refer to collies and spaniels but not to chihuahuas. Such narrower uses are called underextensions. Children sometimes use their words more broadly than the meaning truly allows, calling all four-legged animals doggie or calling all adult males Daddy. These overly broad uses are called overextensions, and at one time, these uses were thought to reveal the meanings that children had assigned to these words in their mental lexicon.

The idea that overextensions provide a window into the nature of the early lexicon was further quashed by careful research, which pointed out that although overextensions are very noticeable when they occur, they are actually not very common. Rescorla (1980) followed 6 children from age 12 months to 18 months and reported that 33% of the children’s word uses were overextended, but only a few different words accounted for a disproportionate share of those overextensions.

There is good evidence that overextensions occur for reasons other than incomplete word meanings. That is, it is not that the child really thinks that the word for horse is dog. One possibility is that the child just doesn’t know or can’t remember what the horse is called and wants to make some comment on it, and dog is the closest word the child can find in his or her vocabulary. Consistent with this view, Rescorla (1980) found that the incidence of overextensions declined as children acquired more differentiated vocabularies (e.g., learning words for animals other than dog). Other findings indicate that overextensions in comprehension are rare and are not predictable from overextensions in production, which further contests the idea that overextensions reflect underlying semantic representation.

The word explosion

Lexical development starts slowly for most children. During the first months after speaking their first words, children add an average of 8 to 11 words to their vocabularies each month. During these months of slow lexical growth, exposure to a new word does not necessarily result in word learning. Words that are apparently learned at one point do not necessarily become permanent additions to children’s productive vocabularies.

For many children, lexical development seems to shift into a different gear at about the 50-word milestone. In this new gear, the rate at which new words appear in the children’s vocabularies increases from 8 to 11 words per month to an average rate of 22 to 37 words per month.

Naming explosion

This explosion occurs for most children sometime around the achievement of a 50-word productive vocabulary or around the age of 18 months. Although many observers have reported a marked increase in the vocabulary growth rate during the second year of life, there is disagreement as to whether all children show this pattern or whether such a thing as an explosion exists at all.

P. Bloom (2000) has argued that the word explosion is a myth. The rate of children’s word learning does accelerate in their second year, but, according to Bloom, the change for most children is a gradual increase rather than an abrupt change in rate. In individual cases, abrupt changes may occur for a variety of reasons. A child may briefly plateau, in which case a return to lexical growth might look like an explosion, or a child’s word-learning opportunity might change. The child who goes on vacation and is exposed to many new things will increase their rate of vocabulary learning. Many such stories are possible. Bloom’s point is that there is no general developmental phenomenon that needs an explanation.

Goldfield and Reznick (1990) have claimed that an explosion occurs in some children and that other children show more even rates of vocabulary development. They carefully documented the rate of vocabulary development in 18 children whom they studied from the age of 14 months until each child achieved a 75-word vocabulary. Children who showed a vocabulary explosion showed a larger, concurrent increase in the proportion of object labels in their vocabulary, whereas the “non-spurters” did not. A word explosion is part of the typical course of lexical development; there is evidence that children younger than 18 months or with vocabularies of fewer than 50 words are not as good at learning new words in an experimental situation as are older children or those with larger vocabularies.

What causes changes in word-learning efficiency?

Although not everyone agrees that there is a word explosion, many have proposed explanations for the word explosion. According to some accounts, the onset or maturation of internal word-learning constraints occurs at this point. Reaching the threshold of a 50-word vocabulary gives children a basis for figuring out principles of how the lexicon works. Nazzi and Bertoncini (2003) have proposed that, at 18 months, children come to understand that words refer not just to particular objects but to object categories.

It has also been pointed out that children’s phonological abilities influence their very early vocabularies, raising the possibility that changes in the nature of children’s phonological systems contribute to the word explosion. The critical underlying change comes from ongoing cognitive development. That many changes in children’s word-learning abilities occur after word learning begins, with the result that word learning becomes increasingly efficient. When critical points in these multiple developments coincide, the rate of word learning might change abruptly - and could be called an explosion.

Word comprehension

The course of the development of word comprehension is another source of evidence of the internal changes that occur as children’s mental lexicons develop. Word learning begins months before children speak their first words. Children as young as 5 months selectively respond to certain words. The first words they seem to respond to is their own name. Anecdotal evidence that infants recognize their own names is common.

At around the age of 8 months, children begin to understand a few phrases, such as “Give me a hug”, “stop it” or “come here”. Shortly after that, between the age of 8 and 10 months, children start to understand the meanings of individual words.

Milestones comprehension skills (0-18 months)

• Attends to a speaker’s voice by orienting toward the speaker 5 times
• Responds to hearing his own name
• Looks at, touches, or points to the correct family