Average American child at 12 months understands about 50 words (Fenson et al. 1994) and can learn a new word every two hours (Pinker 1994)

From as early as 7 months, children begin to comprehend words; comprehension precedes production

The criterion for a spurt is 10 or more words in two and a half weeks

In English, Bates et al. (1994) found that nouns increase when vocabulary grows to between 50-100 words, verbs and adjectives at 100-400 words and function words after 400 words

Receptive vocabulary can be measured by indexes like the MacArthur-Bates Communicative Development Inventory (MBCDI)

Receptive vocabulary is seen to contain many more verbs (Gentner, 1978), particularly 'light verbs' (used in a lot of environments e.g. make; go)

Fast mapping/rapid learning studies show that children can acquire a word based on one or very few exposures (Carey 1978) (see study on teaching pre-schoolers a new colour term)

The reference problem: how does a child map the word onto the correct aspect of the visual scene?

For object class words, there are two parts to the word learning problem: the mapping problem (mapping the word onto its referent); the categorisation problem (extending the word to other members of the category, defining class inclusion)

This principle guides categorisation, biasing taxonomic relations over thematic relations

Despite the fact that children are inherently interested in thematic relationships, they will not extend a label on the basis of a thematic relationship

It hypothesises that if children already know the name of an object, they will not take a novel term to refer to the same object, but instead to a part of the object or its material etc.

Syntactic bootstrapping refers to using knowledge of syntax to learn the meaning of words

If the correlation between meaning and syntactic structure (e.g. transitive vs. distransitive) hold, this can be used as a tool for learning verb meaning

Characterised by children having very early (argued within first month or first two years), regular, and continued exposure to more than one language; there is Language A and Language Alpha

Examples are caregivers with different L1s, or caregivers who have the same L1, but this differs to the surrounding community e.g. daycare

Characterised by the L1 being essentially acquired before the learning of L2 commences; NB that the age at which a child is considered successive rather than simultaneous is subject to discussion

Example contexts include immigration and learning a language in a school/educational context

Bilingual children are valued in language acquisition studies as they are considered a 'perfect matched pair' and allow non-linguistic factors e.g. maturity/ cognitive development to be factored out

Note that first words may be slightly delayed, although still within the expected age range. On the other hand, they might not be delayed, but result from differences in the lexicons, or preferences for a word in one language than another, for example

Language mixing: a speaker alternates between two or more languages within a single sentence or utterance, incorporating elements from one language into another. This mixing may occur because of a lack of vocabulary in one language, cultural influence, or stylistic purposes

Stage one: up to about 1;8, characterised by one lexicon and one primitive set of rules, evidenced by the lack of translation equivalents (only one word is used for one thing/concept) and the mutual exclusivity constraint (avoids synonyms with children using one term if languages aren't perceived to be separate)

Stage two: from 1;8-2;8, characterised by two lexicons and one set of syntactic rules. This is evidenced by the presence of TEs, using different words in language A and language Alpha. One grammatical system is used across languages

Stage three: from 2;9, characterised by two lexicons and two sets of syntactic rules

Problems with the Single-System Hypothesis:

• TEs can appear in early bilingual utterances
• Utterances can be produced with target-like word order despite reverse ordering occurring between languages
• Different languages have different developmental paths e.g. RIs

Posits that children have two separate grammars and lexicons from the beginning of development

Simultaneous bilingual children seem to follow roughly the same development sequence in each language(s) as monolingual speakers do

Bilingual children construct grammars in the same way as monolingual children

Early separation of languages is evident in the production of subjects and RIs; children produce more subjects in their non-null subject language than in the null subject language, and they produce RIs in tandem with monolinguals

There is no specific delay in acquiring two languages over acquiring one language, except with respect to lexicon (total number of words across two languages is comparable to monolinguals in early stages)

Code-switching suggests that although the bilingual's language systems are separate, there is some interconnection between the two systems

Successive/sequential bilingualism: the second language is introduced when the first language acquisition is already well underway (after around 3 years)

It takes a child much less time to acquire L2 than L1; children reach the level of their monolingual peers after around one year (3-7 years-old)

There is a transfer from the L1 to L2, meaning that L2 acquisition is influenced by the first

Instead of trying to imitate native speakers, L2 learners try to uncover the rules of the target language

However, being older, L2 learners may be disadvantaged to attaining native-like proficiency such as pronunciation and inflectional morphology

E.g. vocabulary learning in older L2 children benefits from greater cognitive skills and pre-existing labels in L1. Older children may also start learning an L2 using more complex and longer sentences

Young children may speak a language in the home which they do not use in the wider community (e.g. in instances of immigration), and may not encounter the majority language until schooling at around age 5

This may be due to exposure to the dominant language in the community (e.g. via media), or language used by peers

Attrition is characterised by a loss of vocabulary, complex syntactic structures and production ability. Despite this, comprehension is usually retained (passive/ receptive bilingual: comprehension but no production)

Any language acquired as a child, or later, has the potential to be lost and regained throughout the lifespan

A heritage language learner is someone who, as an adolescent or adult, starts to re-aquire or improve L1 language skills