Vocabulary development
Vocabulary development is a process by which people acquire words. Babbling shifts towards meaningful speech as infants grow and produce their first words around the age of one year. In early word learning, infants build their vocabulary slowly. By the age of 18 months, infants can typically produce about 50 words and begin to make word combinations.
In order to build their vocabularies, infants must learn about the meanings that words carry. The mapping problem asks how infants correctly learn to attach words to referents. Constraints theories, domain-general views, social-pragmatic accounts, and an emergentist coalition model have been proposed to account for the mapping problem.
From an early age, infants use language to communicate. Caregivers and other family members use language to teach children how to act in society. In their interactions with peers, children have the opportunity to learn about unique conversational roles. Through pragmatic directions, adults often offer children cues for understanding the meaning of words.
Throughout their school years, children continue to build their vocabulary. In particular, children begin to learn abstract words. Beginning around age 3–5, word learning takes place both in conversation and through reading. Word learning often involves physical context, builds on prior knowledge, takes place in social context, and includes semantic support. The phonological loop and serial order short-term memory may both play an important role in vocabulary development.
Early word learning
Infants begin to understand words such as "Mommy", "Daddy", "hands" and "feet" when they are approximately 6 months old.[2][3] Initially, these words refer to their own mother or father or hands or feet. Infants begin to produce their first words when they are approximately one year old.[4][5] Infants' first words are normally used in reference to things that are of importance to them, such as objects, body parts, people, and relevant actions. Also, the first words that infants produce are mostly single-syllabic or repeated single syllables, such as "no" and "dada".[5] By 12 to 18 months of age, children's vocabularies often contain words such as "kitty", "bottle", "doll", "car" and "eye". Children's understanding of names for objects and people usually precedes their understanding of words that describe actions and relationships. "One" and "two" are the first number words that children learn between the ages of one and two. Infants must be able to hear and play with sounds in their environment, and to break up various phonetic units to discover words and their related meanings.
Studies related to vocabulary development show that children's language competence depends upon their ability to hear sounds during infancy.[4][7][8] Infants' perception of speech is distinct. Between six and ten months of age, infants can discriminate sounds used in the languages of the world.[4] By 10 to 12 months, infants can no longer discriminate between speech sounds that are not used in the language(s) to which they are exposed.[4] Among six-month-old infants, seen articulations (i.e. the mouth movements they observe others make while talking) actually enhance their ability to discriminate sounds, and may also contribute to infants' ability to learn phonemic boundaries.[9] Infants' phonological register is completed between the ages of 18 months and 7 years.
Children's phonological development normally proceeds as follows:[4]
6–8 weeks: Cooing appears
16 weeks: Laughter and vocal play appear
6–9 months: Reduplicated (canonical) babbling appears
12 months: First words use a limited sound repertoire
18 months: Phonological processes (deformations of target sounds) become systematic
18 months–7 years: Phonological inventory completion
At each stage mentioned above, children play with sounds and learn methods to help them learn words.[7] There is a relationship between children's prelinguistic phonetic skills and their lexical progress at age two: failure to develop the required phonetic skills in their prelinguistic period results in children's delay in producing words.[10] Environmental influences may affect children's phonological development, such as hearing loss as a result of ear infections.[4] Deaf infants and children with hearing problems due to infections are usually delayed in the beginning of vocal babbling.
Babbling is an important aspect of vocabulary development in infants, since it appears to help practice producing speech sounds.[11] Babbling begins between five and seven months of age. At this stage, babies start to play with sounds that are not used to express their emotional or physical states, such as sounds of consonants and vowels.[7] Babies begin to babble in real syllables such as "ba-ba-ba, neh-neh-neh, and dee-dee-dee,"[7] between the ages of seven and eight months; this is known as canonical babbling.[4] Jargon babbling includes strings of such sounds; this type of babbling uses intonation but doesn't convey meaning. The phonemes and syllabic patterns produced by infants begin to be distinctive to particular languages during this period (e.g., increased nasal stops in French and Japanese babies) though most of their sounds are similar.[4][7] There is a shift from babbling to the use of words as the infant grows.[12]
As children get older their rate of vocabulary growth increases. Children probably understand their first 50 words before they produce them. By the age of eighteen months, children typically attain a vocabulary of 50 words in production, and between two and three times greater in comprehension.[5][7] A switch from an early stage of slow vocabulary growth to a later stage of faster growth is referred to as the vocabulary spurt.[13] Young toddlers acquire one to three words per month. A vocabulary spurt often occurs over time as the number of words learned accelerates. It is believed that most children add about 10 to 20 new words a week.[13] Between the ages of 18 to 24 months, children learn how to combine two words such as no bye-bye and more please.[5] Three-word and four-word combinations appear when most of the child's utterances are two-word productions. In addition, children are able to form conjoined sentences, using and.[5] This suggests that there is a vocabulary spurt between the time that the child's first word appears, and when the child is able to form more than two words, and eventually, sentences. However, there have been arguments as to whether or not there is a spurt in acquisition of words. In one study of 38 children, only five of the children had an inflection point in their rate of word acquisition as opposed to a quadratic growth.[13]
The learning mechanisms involved in language acquisition are not specific to oral languages. The developmental stages in learning a sign language and an oral language are generally the same. Deaf babies who are exposed to sign language from birth will start babbling with their hands from 10 to 14 months. Just as in oral languages, manual babbling consists of a syllabic structure and is often reduplicated. The first symbolic sign is produced around the age of 1 year.
Young children will simplify complex adult signs, especially those with difficult handshapes. This is likely due to fine motor control not having fully developed yet. The sign's movement is also often proximalized: the child will articulate the sign with a body part that is closer to the torso. For example, a sign that requires bending the elbow might be produced by using the shoulder instead. This simplification is systematic in that these errors are not random, but predictable.
Signers can represent the alphabet through the use of fingerspelling. Children start fingerspelling as early as the age of 2. However, they are not aware of the association between fingerspelling and alphabet. It is not until the age of 4 that they realize that fingerspelling consists of a fixed sequence of units.
Mapping problem
In word learning, the mapping problem refers to the question of how infants attach the forms of language to the things that they experience in the world.[16] There are infinite objects, concepts, and actions in the world that words could be mapped onto.[16] Many theories have been proposed to account for the way in which the language learner successfully maps words onto the correct objects, concepts, and actions.
While domain-specific accounts of word learning argue for innate constraints that limit infants' hypotheses about word meanings,[17] domain-general perspectives argue that word learning can be accounted for by general cognitive processes, such as learning and memory, which are not specific to language.[18] Yet other theorists have proposed social pragmatic accounts, which stress the role of caregivers in guiding infants through the word learning process.[19] According to some[who?] research, however, children are active participants in their own word learning, although caregivers may still play an important role in this process.[20][21] Recently, an emergentist coalition model has also been proposed to suggest that word learning cannot be fully attributed to a single factor. Instead, a variety of cues, including salient and social cues, may be utilized by infants at different points in their vocabulary development.[1]
Theories of word-learning constraints argue for biases or default assumptions that guide the infant through the word learning process. Constraints are outside of the infant's control and are believed to help the infant limit their hypotheses about the meaning of words that they encounter daily.[17][22] Constraints can be considered domain-specific (unique to language).
Critics[who?] argue that theories of constraints focus on how children learn nouns, but ignore other aspects of their word learning.[23] Although constraints are useful in explaining how children limit possible meanings when learning novel words, the same constraints would eventually need to be overridden because they are not utilized in adult language.[24] For instance, adult speakers often use several terms, each term meaning something slightly different, when referring to one entity, such as a family pet. This practice would violate the mutual exclusivity constraint.
Below, the most prominent constraints in the literature are detailed:
· Reference is the notion that a word symbolizes or stands in for an object, action, or event.Words consistently stand for their referents, even if referents are not physically present in context.
· Mutual Exclusivity is the assumption that each object in the world can only be referred to by a single label.
· Shape has been considered to be one of the most critical properties for identifying members of an object category. Infants assume that objects that have the same shape also share a name. Shape plays an important role in both appropriate and inappropriate extensions.
· The Whole Object Assumption is the belief that labels refer to whole objects instead of parts or properties of those objects. Children are believed to hold this assumption because they typically label whole objects first, and parts of properties of objects later in development.
· The Taxonomic Assumption reflects the belief that speakers use words to refer to categories that are internally consistent. Labels to pick out coherent categories of objects, rather than those objects and the things that are related to them.[17][30] For example, children assume that the word "dog" refers to the category of "dogs", not to "dogs with bones", or "dogs chasing cats"