The relation of lexical and grammatical knowledge is at the core of many controversies in linguistics and psycholinguistics. Recent empirical findings that the two are highly correlated in early language development have further energized the theoretical debate. Behavioural genetics provides an illuminating new tool to explore this question, by addressing the question of whether the empirical correlation simply reflects the fact that environments which facilitate one aspect of language growth also facilitate the other, or whether the same underlying acquisition mechanisms, influenced by the same genes, are responsible for the correlation. We explored this issue in a study of 2898 pairs of two-year-old twins born in England and Wales. Language development was assessed by their parents using an adapted version of the MacArthur Communicative Development Inventory which assesses vocabulary and grammar. Moderate heritabilities were found for both. As in previous studies, measures of vocabulary and sentence complexity were substantially correlated (r = 0·66). Behaviour-genetic modelling of the relation of vocabulary and grammar produced an estimated value of 0·61 for the genetic correlation, a measure of the overlap of the genetic effects that contribute to the two aspects of language development. In contrast, a measure of nonverbal cognitive development, the PARCA, was only weakly correlated at both the phenotypic level and at the level of genetic correlations with the language measures. Thus, although the distinction between verbal and nonverbal skills has a genetic basis underlying the phenotypic dissociation, there is little evidence either genetically or phenotypically for a dissociation between vocabulary and grammar within language.

Previous evidence suggests that the structure of similarity neighbourhoods in the developing mental lexicon may differ from that of the fully developed lexicon. The similarity relationships used to organize words into neighbourhoods was investigated in 20 pre-school children (age 3;7 to 5;11) using a two alternative forced-choice classification task. Children classified the similarity of test words relative to a standard word to determine neighbourhood membership. The similarity relationship between the test and standard words varied orthogonally in terms of type of similarity and position of overlap. Standard words were drawn from neighbourhoods differing in density. Results showed that dense neighbourhoods were organized by phoneme similarity in the onset+nucleus or rhyme positions of overlap. In contrast, sparse neighbourhoods appeared to be organized by phoneme similarity in the onset+nucleus, but manner similarity in the rhyme. These results are integrated with previous findings from infants and adults to propose a developmental course of change in the mental lexicon.

This paper traces the process involved in the bilingual infant's gradual differentiation of his two languages, beginning with the acquisition of a dual lexicon. Word combination is at first based indiscriminately on this dual language source; function words account for a disproportionately large number of tokens used in mixed-language utterances. Universal principles of child syntax are at first applied; later, rules specific to each of the languages are developed separately. The development of self-awareness and sensitivity to standards in the second year provides the essential cognitive underpinning for the child to begin to avoid mixed-language utterances and to choose his language according to his interlocutor. At a still later point the bilingual older child may begin to make use of code-switching strategies appropriate to his or her bilingual community.

Adult recasts of child utterances have been shown to be related in a general way to the child's acquisition of syntactic structures. The current study had two aims. The first aim was to determine which feature(s) of recasts (i.e. reformulation, expansion, topic continuation, or reply) was responsible for facilitating language acquisition by comparing them to other maternal discourse models that were systematically defined by these properties. The second aim was to investigate this relation more specifically by relating adult discourse models of specific grammatical morphemes to the child's acquisition of those same morphemes. Again, recasts were of particular interest. Twelve mother-child dyads were videorecorded during one hour of naturalistic interaction when the children were 1;10 and 2;4. Results indicated that maternal recasts of specific morphemes were related to the acquisition of those same grammatical morphemes during certain developmental periods, whereas other grammatical morphemes were facilitated by expansions and topic continuations. These results are discussed in terms of the processes responsible for these effects.

Early acquisition of nouns and verbs across languages is a key issue for a number of recent studies that question the reality of the ‘noun-bias’ and wonder about the reasons why it exists as they explore the role of cognitive vs. more language-specific input factors. Addressing this issue, the present study investigates how the noun and verb word classes develop in the free speech of a French child between the ages of 1;2 and 2;6, from the perspective of semantic and grammatical development. The analyses indicate that, in French acquisition, nouns clearly predominate over verbs until age 1;8 at least, but that verbs are produced in the early stages. Concrete object names among nouns and concrete action verbs among verbs were found to be the most prevalent categories, but they were not the earliest to appear and their distribution revealed an asymmetry in the conceptual packaging of nouns and verbs. Verb grammaticalization, assessed through inflection and auxiliary use, lagged somewhat behind noun grammaticalization, assessed through determiner use. This result supports the hypothesized noun–verb grammatical asynchrony. Verb grammaticalization seems to be related to the production of concrete action verbs, and noun grammaticalization to that of concrete object nouns, indicating interactions between semantic and grammatical development. These findings, discussed in a cross-linguistic perspective, suggest that both conceptual and grammatical packaging are important and interacting factors in noun and verb development, and argue in favour of a constructivist approach to language acquisition.

The productive narrative competence of three young children as revealed in their spontaneously occurring conversations recorded over an 18-month period during their kindergarten and grade one years was investigated. Almost 90 hours of the children's conversations, produced as they were being driven to and from school, were audiotaped and analysed in order to determine whether children between the ages of five and seven include narrative accounts in their conversations with each other and, if so, the nature of the narrative language produced. The subjects were found routinely and regularly to produce a striking variety of narrative forms; 14 different narrative types were distinguished and defined, six of which have not previously been reported in the literature on children's narratives. Seventy per cent of the recorded narratives took anecdotal form; original fantasy narratives occurred only rarely. A significant proportion of the narratives were collaboratively created.

Giving good definitions requires controlling both word meaning and definitional form. Definitions from 137 second to fifth graders (i.e. aged seven to eleven) were scored to reflect conformity to the classic Aristotelian form and quality of information provided. Comparisons among children with different backgrounds indicated that school exposure to English was strongly related to per cent formal definitions given and their quality. 63 children were also tested in French, their foreign language. Performance in French was lower than in English; exposure to French at home related to the amount of information the children provided in informal definitions, not to quality of formal definitions. The results suggest that performance on definitions is most strongly affected by opportunities to practise the required form.

Young children learning English as well as many other languages frequently omit weakly stressed syllables from multisyllabic words. In particular, they are more likely to omit weak syllables from word-initial positions than from word-internal or -final positions. For example, the weak syllable of a weak-strong (WS) word like giraffe is much more likely to be omitted than the weak syllable of a SW word like tiger. Three hypotheses for this omission pattern have been offered. In two, children's weak syllable omissions reflect innate perceptual biases either to ignore initial weak syllables or to encode word-final syllables. In contrast, the SW Production Template Hypothesis states that children have a template for producing a strong syllable followed by an optional weak syllable. When they apply a series of SW templates to their intended utterances, weak syllables that do not fit the templates are more likely to be omitted than those that do. To compare the three hypotheses, young two-year-olds were asked to say four-syllable SWWS and WSWS nonsense words. Children's pattern of weak syllable preservations was highly consistent with the SW production template hypothesis, but not with the perception-based hypotheses. Implications of this research for children's function morpheme omissions and for the relation of metrical and segmental production templates are discussed.

The influence of phonological (i.e. individual sounds), lexical (i.e. whole-word forms) and semantic (i.e. meaning) characteristics on the words known by infants age 1 ; 4 to 2 ; 6 was examined, using an existing database (Dale & Fenson, 1996). For each noun, word frequency, two phonological (i.e. positional segment average, biphone average), two lexical (i.e. neighborhood density, word length) and four semantic variables (i.e. semantic set size, connectivity, probability resonance, resonance strength) were computed. Regression analyses showed that more infants knew (1) words composed of low-probability sounds and sound pairs, (2) shorter words with high neighborhood density, and (3) words that were semantically related to other words, both in terms of the number and strength of semantic connections. Moreover, the effect of phonological variables was constant across age, whereas the effect of lexical and semantic variables changed across age.

Several studies have argued that children under the ages of nine or ten years rarely comprehend figurative language and therefore interpret it literally. Cacciari & Levorato (1989). showed that when idioms are presented within a rich informational environment, children are able to grasp the figurative sense at the age of seven, and also that children are less able to produce idioms than to comprehend them. In three experiments involving 264 children (whose age ranged from 6;9 to 11;9), we contrasted this global elaboration hypothesis with a partially alternative one, the acquisition via exposure hypothesis, according to which the frequency of exposure of children to idioms is the main factor explaining their acquisition and production. Results showed that familiarity (i.e. frequency of exposure) plays a minor role and only for children who are not yet able to use contextual information. Familiarity per se does not adequately explain how children acquire a figurative competence. A tentative model is proposed in order to account for figurative competence acquisition.

Samples of babbling productions of 6-, 8- and 10-month-old infants from different language backgrounds were presented to adult judges whose task was to identify the infants from their own linguistic community. The results show that certain language-specific metaphonological cues render this identification possible when the samples exhibit long and coherent intonation patterns. The segmental indications that are present in the fully syllabic productions of canonical babbling do not allow the judges to identify the infants correctly from their own linguistic community. These results seem to support the hypothesis of an early influence on babbling of the metaphonological characteristics of the target language.

Previous studies have demonstrated that children aged 2;0 can learn new words in a variety of non-ostensive contexts. The current two studies were aimed at seeing if this was also true of children just beginning to learn words at 1;6. In the first study an adult interacted with 48 children. She used a nonce word to announce her intention to find an object (‘Let's find the gazzer’), picked up and rejected an object with obvious disappointment, and then gleefully found the target object (using no language). Children learned the new word as well in this condition as in a condition in which the adult found the object immediately. In the second study the adult first played several rounds of a finding game with each of 60 children, in which it was first established that one of several novel objects was always in a very distinctive hiding place (a toy barn). The adult then used a nonce word to announce her intention to find an object (‘Let's find the toma’) and then proceeded to the barn. In the key condition the barn was mysteriously ‘locked’; the child thus never saw the target object after the nonce word was introduced. Children learned the new word as well in this condition as in a condition in which the adult found the object immediately. The results of these two studies suggest that from very early in language acquisition children learn words not through passive, associative pro- cesses, but rather through active attempts to understand adult behaviour in a variety of action and discourse contexts.

Patterns of vowel articulation in conversational speech to an adult and to child listeners were analysed in the speech of nine mothers. Formant frequency analysis of vowels embedded in 2,406 words found in varying syntactic environments and uttered by women to pre-verbal, holophrastic and more advanced child listeners (MLUs 2·5–4·0) revealed an emerging pattern of content word clarification, as measured by wider dispersion and decreased overlap between vowel phoneme categories in formant characteristics. Additionally, function word clarification was noted in speech to the oldest children. Vowel production appears to be modulated by child–addressee language ability. Earlier studies suggesting a lack of phonetic clarification in mother–child speech may have investigated speech to children too mature to elicit maternal clarification behaviours.

Spontaneous full passives and related constructions from 234 children aged 2; 0 to 13; 11 and elicited passives from 262 college students were analysed. Full passives were classified as REVERSIBLE (The dog was chased by the girl), INSTRUMENTAL NON-REVERSIBLE (The lamp was broken by (or with) the ball), or AGENTIVE NON-REVERSIBLE (The lamp was broken by the girl). The Agentive non-reversible did not appear until after age 9; and until age 11 no child produced both Reversible and Non-reversible passives. All the children used the passive in a semantically restricted way (but not in the same way). The possible developmental course of the full passive was traced for children who initially used only Reversible passives versus those who initially used only Instrumental non-reversible passives.

The first verbs to participate in VO and SVO combinations, and the temporal parameters of the spread of these combinatory patterns over different verbs were investigated. The longitudinal language observations of 16 children, one acquiring English, the others Hebrew, were examined. The children were observed once a week for 3–12 months, the observations starting when the children were still in the single-word stage (1;1–2;1) and ending when they were well into multiword speech (1;8–2;7). The results indicate that the more verbs children already know to combine in a certain pattern, the faster they learn new ones. Apparently children induce from individual word-combinations some general principles that facilitate further learning. The ‘pathbreaking verbs’ that begin the acquisition of a novel syntactic rule tend to be generic verbs expressing the relevant combinatorial property in a relatively pure fashion: the same verbs that children first combine with direct objects, are typical grammaticalized markers of transitivity in many languages. These verbs do not have HIGH TRANSITIVITY as defined by Hopper & Thompson (1980). Rather, they express fundamental ‘object relations’ of incorporation into, and ejection from the personal. Crosslinguistic evidence indicates that this may be the basic transitivity construct in languages. The results raise the possibility that lexical-specific learning of positional patterns is sufficient to account for the formation of syntactic abstractions.

The existence of stylistic variation between children in the early stages of language acquisition has been most frequently studied using Nelson's 0973) referential—expressive distinction. While the use of this distinction has generated a great deal of interesting research, there are a number of major problems associated with it. The present study presents a simple scheme, based on formal categories, for coding stylistic variation in the early lexicon. When applied to the first 50 and 100 words of 12 children collected between 0; 11 and 2; 3, the major dimensions of difference are found to be the relative proportion of common nouns and the relative proportion of frozen phrases. Moreover, the proportion of frozen phrases is also found to be significantly positively related to children's early productivity, suggesting that, rather than being a ‘deadend’ in early language development, the acquisition of frozen phrases may provide an alternative route into multiword speech.

Cultural, linguistic, and developmental evidence was taken into consideration in constructing the HCDI, a Hebrew adaptation of the MCDI. The HCDI was then administered to a stratified sample of Israeli mothers of 253 toddlers aged 1; 6 to 2; 0 (M = 1; 8·18). Hebrew results are presented and compared with scores from the original MCDI sample (Fenson, Dale, Reznick, Bates, Thal & Pethick, 1994). The HCDI is a reliable and sensitive measure of lexical development and emergent grammar, capturing wide variability among Israeli toddlers. In comparison with English, the relation between vocabulary size and age, as well as the shape of the growth curves for nouns, predicate terms, and closed class words relative to size of lexicon, were strikingly similar. These results indicate that conclusions concerning cross-linguistic similarities can be best documented by using parallel methods of measurement. The HCDI results support the claim that early lexical development in Hebrew and in English follow remarkably similar development patterns, despite the typological differences between the two target languages.

Beliefs about whether or not children receive corrective input for grammatical errors depend crucially on how one defines the concept of correction. Arguably, previous conceptualizations do not provide a viable basis for empirical research (Gold, 1967; Brown & Hanlon, 1970; Hirsh-Pasek, Treiman & Schneiderman, 1984). Within the Contrast Theory of negative input, an alternative definition of negative evidence is offered, based on the idea that the unique discourse structure created in the juxtaposition of child error and adult correct form can reveal to the child the contrast, or conflict, between the two forms, and hence provide a basis for rejecting the erroneous form. A within-subjects experimental design was implemented for 36 children (mean age 5;0), in order to compare the immediate effects of negative evidence with those of positive input, on the acquisition of six novel irregular past tense forms. Children reproduced the correct irregular model more often, and persisted with fewer errors, following negative evidence rather than positive input.

This study examined the relationship between mothers' speech and the rate of child syntax growth for 22 2½-year-old children whose speech was sampled at two-month intervals over a six-month period. The relations which appeared suggest that linguistic experience does contribute to syntax development, but that the relation between linguistic input and language growth is different for different domains of language and at different points in the course of development. The results further suggest that there are multiple bases to the benefit of input to language acquisition. One mechanism particularly suggested by the findings is that children analyse the distributional properties of the speech they hear and may induce linguistic structure from the relationship between the structural properties of adjacent utterances in discourse.

This study examined children's production and comprehension of questions, with the aim of discovering possible patterns in question acquisition. For the production study, questions were collected from 22 children aged 2; 0–3; 11. The data show a high frequency of yes-no, what, and where questions by age 2; 0. Why and how questions were infrequent but they increased with age. Who and when questions were rarely asked by children of any age. From the frequency data a rough chronological order of acquisition was inferred: what, where, why, how, when. In the comprehension study 100 children were tested, aged 3; 0–5; 5. The test controlled syntax and vocabulary and varied specific wh- question-words. The frequency of correct answers increased with the age of the children. When children made mistakes, their answers were not random but appeared to be following certain question-answering strategies. These included attention to semantic features of verbs and especially the placement of verbs in the sentence.