Analysing the gradual learning process through which a child becomes bilingual from early infancy, three stages can be distinguished: (1) the child has one lexical system which includes words from both languages; (2) the child distinguishes two different lexicons but applies the same syntactic rules to both languages; (3) the child has two linguistic codes, differentiated both in lexicon and in syntax, but each language is exclusively associated with the person using that language. Only at the end of this stage, when the tendency to categorize people in terms of their language decreases, can one say that a child is truly bilingual.

It has been claimed that children simultaneously acquiring two languages go through an initial stage when they are unable to differentiate between their two languages. Such claims have been based on the observation that at times virtually all bilingual children mix elements (e.g. lexical, morphological) from their two languages in the same utterance. That most, if not all, children acquiring two languages simultaneously mix linguistic elements in this way is widely documented. Although such code-mixing is not well understood or explained, there are a number of explanations unrelated to lack of language differentiation that may explain it. Moreover, while language differentiation is widely attested among bilingual children once functional categories emerge, usually during the third year, there is still some question as to how early in development differentiation is present. In this study, we examined language differentiation in five bilingual children prior to the emergence of functional categories (they ranged in age from 1;10 to 2;2 and in MLU from 1·23 to 2·08). They were observed with each parent separately and both together, on separate occasions. Our results indicate that while these children did code mix, they were clearly able to differentiate between their two languages. We also examine the possibility that the children's mixing is due to (a) their language dominance, and (b) their parents' rate of mixing. We could find no evidence that their mixing was due to parental input, but there was some evidence that language dominance played a role.

Parent report data on early language development measured using the MacArthur Communicative Development Inventory (CDI–Infant Form) was collected on 134 preschool children with autism spectrum disorder. The pattern of development of understanding of phrases, word comprehension and expression, and production of gestures, was compared to the typical pattern. In common with typical development there was considerable variability in language acquisition, although for the group as a whole this was significantly delayed compared to the normal course. In addition, atypical patterns were identified in the emergence of language skills in the sample. Comprehension of words was delayed in comparison to word production, and production of early gestures (involving sharing reference) was delayed relative to production of later gestures (involving use of objects). However, other aspects of language development were similar to that found in typically developing infants, including word comprehension being in advance of word production in absolute terms, gesture production acting as a ‘bridge’ between word comprehension and word production and the broad pattern of acquisition across word categories and word forms. The implications for assessment and intervention with preschool children with autism spectrum disorder are discussed.

When carefully assessed and analysed, parent report can provide a valuable overall evaluation of children's language at 20 months. Norming information and validity coefficients are presented here for a vocabulary checklist assessment included in the Early Language Inventory. Normative data are provided for fullterm, preterm, and precocious samples, including selected vocabulatory subsets that are indicative of early language learning style. The vocabulary checklist has substantial validity as indexed by correlations with the Bayley Scales of Infant Development and particularly with a language subscale derived from that test.

This review article presents evidence for the claim that frequency effects are pervasive in children's first language acquisition, and hence constitute a phenomenon that any successful account must explain. The article is organized around four key domains of research: children's acquisition of single words, inflectional morphology, simple syntactic constructions, and more advanced constructions. In presenting this evidence, we develop five theses. (i) There exist different types of frequency effect, from effects at the level of concrete lexical strings to effects at the level of abstract cues to thematic-role assignment, as well as effects of both token and type, and absolute and relative, frequency. High-frequency forms are (ii) early acquired and (iii) prevent errors in contexts where they are the target, but also (iv) cause errors in contexts in which a competing lower-frequency form is the target. (v) Frequency effects interact with other factors (e.g. serial position, utterance length), and the patterning of these interactions is generally informative with regard to the nature of the learning mechanism. We conclude by arguing that any successful account of language acquisition, from whatever theoretical standpoint, must be frequency sensitive to the extent that it can explain the effects documented in this review, and outline some types of account that do and do not meet this criterion.

Our understanding of the relationships between lexical and phonological development has been enhanced in recent years by increased interest in this area from language scientists, psychologists and phonologists. This review article provides a summary of research, highlighting similarities and differences across studies. It is suggested that the research falls into two categories with different goals and different methodological approaches: (1) child-centered studies that examine the influences active in the prelinguistic and early-word period, emphasizing individual developmental patterns and the active role played by the child; and (2) studies inspired by research on word processing in adults; these focus on the effects of the phonological and lexical characteristics of the ambient language on underlying representations and word learning in children. The article concludes with suggestions for integrating the findings from the two approaches and for future research.

Twenty economically disadvantaged preschoolers (mean age 3;7) were randomly assigned to an intervention or a control group, and their mothers' styles of eliciting narratives from their children were assessed before and after intervention. Mothers of intervention children were encouraged to spend more time in narrative conversation, ask more open-ended and context-eliciting questions, and encourage longer narratives through back-channel responses. Children's narrative and vocabulary skills were assessed before and after the year-long intervention and 14 children participated in a follow-up assessment a year later. Narrative measures included the number and length of narratives as well as how decontextualized and informative they were. Intervention children showed significant vocabulary improvement immediately after intervention terminated, and a year later they showed overall improvements in narrative skill. In particular, intervention children produced more context-setting descriptions about where and especially when the described events took place. Such decontextualized language has been emphasized as important for literacy acquisition.

The arguments both for and against viewing the child's initial one-word utterances as HOLOPHRASES are reviewed. Some theoretical problems – concerning the innateness of language, the acquisition of syntax, the status of prosody and the child's comprehension of language during the one-word stage – with the holophrase controversy are pointed out. We suggest that an unresolvable theoretical stalemate exists because proponents on both sides of the controversy mistakenly assume the centrality of the notion sentence in discussing holophrases. An alternative view of early language development, which takes the SPEECH ACT as the basic unit of linguistic communication, is offered as a solution to the problems with the holophrase controversy as it now stands. We propose a more integrated description of the relations between functional and grammatical aspects of early communicative competence than is currently provided by sentence-oriented theories. In particular, we suggest that the child's PRAGMATIC INTENTIONS gradually become GRAMMATICALIZED as semantic and syntactic structures. Finally, three entities – communicative functions, referring expressions and predicating expressions – are proposed as LANGUAGE UNIVERSALS, as distinct from grammatical universals.

The speech of 6 mothers to their healthy infants was examined longitudinally during the neonatal period and at 4, 12, and 24 months in a semi-naturalistic setting. Features of speech analysed were: contour of fundamental frequency, repetitiveness, timing (durations of vocalizations and pauses), tempo and MLU. The neonatal period was characterized by elongated pauses. During the 4-month period the extent of pitch contouring and repetitiveness was greater than at earlier or later ages. By 24 months, the duration of vocalizations and length of MLU became markedly greater. The period of intense face-to-face interaction around the fourth month proved to involve more changes in certain prosodic features. Some of the possible functions of these changes during this phase are discussed.

Studies examining factors that influence when words are learned typically investigate one lexical category or a small set of words. We provide the first evaluation of the relation between input frequency and age of acquisition for a large sample of words. The MacArthur-Bates Communicative Development Inventory provides norming data on age of acquisition for 562 individual words collected from the parents of children aged 0 ; 8 to 2 ; 6. The CHILDES database provides estimates of frequency with which parents use these words with their children (age: 0 ; 7–7 ; 5; mean age: 36 months). For production, across all words higher parental frequency is associated with later acquisition. Within lexical categories, however, higher frequency is related to earlier acquisition. For comprehension, parental frequency correlates significantly with the age of acquisition only for common nouns. Frequency effects change with development. Thus, frequency impacts vocabulary acquisition in a complex interaction with category, modality and developmental stage.

We found that infant gaze following and pointing predicts subsequent language development. At ages 0 ; 10 or 0 ; 11, infants saw an adult turn to look at an object in an experimental setting. Productive vocabulary was assessed longitudinally through two years of age. Growth curve modeling showed that infants who gaze followed and looked longer at the target object had significantly faster vocabulary growth than infants with shorter looks, even with maternal education controlled; adding infant pointing strengthened the model. We highlight the role of social cognition in word learning and emphasize the communicative-referential functions of early gaze following and pointing.

Divergent hypotheses exist concerning the types of knowledge underlying early bilingualism, with some portraying a troubled course marred by language delays and confusion, and others portraying one that is largely unremarkable. We studied the extraordinary case of bilingual acquisition across two modalities to examine these hypotheses. Three children acquiring Langues des Signes Québécoise and French, and three children acquiring French and English (ages at onset approximately 1;0, 2;6 and 3;6 per group) were videotaped regularly over one year while we empirically manipulated novel and familiar speakers of each child's two languages. The results revealed that both groups achieved their early linguistic milestones in each of their languages at the same time (and similarly to monolinguals), produced a substantial number of semantically corresponding words in each of their two languages from their very first words or signs (translation equivalents), and demonstrated sensitivity to the interlocutor's language by altering their language choices. Children did mix their languages to varying degrees, and some persisted in using a language that was not the primary language of the addressee, but the propensity to do both was directly related to their parents' mixing rates, in combination with their own developing language preference. The signing-speaking bilinguals did exploit the modality possibilities, and they did simultaneously mix their signs and speech, but in semantically principled and highly constrained ways. It is concluded that the capacity to differentiate between two languages is well in place prior to first words, and it is hypothesized that this capacity may result from biological mechanisms that permit the discovery of early phonological representations. Reasons why paradoxical views of bilingual acquisition have persisted are also offered.

Communicative Development Inventories (CDIs) were collected from 669 British children aged between 1;0 and 2;1. Comprehension and production scores in each age group are calculated. This provides norming data for the British infant population. The influence of socio-economic group on vocabulary scores is considered and shown not to have a significant effect. The data from British infants is compared to data from American infants (Fenson, Dale, Reznick, Bates, Thal & Pethick, 1994). It is found that British infants have lower scores on both comprehension and production than American infants of the same age.

Pine & Lieven (1993) suggest that a lexically-based positional analysis can account for the structure of a considerable proportion of children's early multiword corpora. The present study tests this claim on a second, larger sample of eleven children aged between 1;0 and 3;0 from a different social background, and extends the analysis to later in development. Results indicate that the positional analysis can account for a mean of 60% of all the children's multiword utterances and that the great majority of all other utterances are defined as frozen by the analysis. Alternative explanations of the data based on hypothesizing underlying syntactic or semantic relations are investigated through analyses of pronoun case marking and of verbs with prototypical agent–patient roles. Neither supports the view that the children's utterances are being produced on the basis of general underlying rules and categories. The implications of widespread distributional learning in early language development are discussed.

This study explores the communicative use of the gestural and vocal modalities by normally developing Italian children during the transition from one- to two-word speech. We analysed the spontaneous production of 12 children at 1;4 and at 1;8, focusing on the use of two-element combinations of words and/or gestures. Results indicated that use of gesture and gesture-word combinations during the transition to two-word speech is a robust feature of communicative development across a relatively large number of children in a rich gestural culture, and that the number of gesture-word and two-word combinations increased significantly from 1;4 to 1;8. Number of gestures and gesture-word combinations produced at 1;4 was also predictive of total vocal production at 1;8. Findings are discussed in terms of the role of gesture as a transitional device en route to two-word speech.

The nature of early games and how they might assist the infant in language acquisition were explored in a longitudinal study of two mother–infant dyads, using video-recordings of their free play. Analysis of appearance and disappearance games, in particular, revealed: (1) a restricted format, with a limited number of semantic elements, and a highly constrained set of semantic relations; (2) a clear repetitive structure, which allowed both for anticipation of the order of events and variation of the individual elements; (3) positions for appropriate vocalizations which could in turn be used to mark variations; and (4) the development of reversible role relationships between mother and child.

This paper reports on a longitudinal study of the acquisition of the voicing contrast in American English word-initial stop consonants, as measured by voice onset time. Four monolingual children were recorded at two-week intervals, beginning when the children were about 1; 6. Data provide evidence for three general stages: (1) the child has no contrast; (2) the child has a contrast but one that falls within the adult perceptual boundaries of one (usually voiced) phoneme and thus is presumably not perceptible to adults; and (3) the child has a contrast that resembles the adult contrast. The rate and nature of the developmental process are discussed in relation to two competing models for phonological acquisition and two hypotheses regarding the skills being learned.

The conclusion that information regarding the grammatically of children's speech is unavailable in parental input has recently been challenged (Moerk 1983 a, b, Hirsh-Pasek, Treiman & Schneiderman 1984). The present study expanded on this research by broadening the definition of ‘negative feedback’ and by describing individual styles of mother–child dialogues. The purpose was to investigate whether mothers of four 2-year-old children responded differentially to their children's well-formed or ill-formed utterances with explicit and implicit feedback. The middle-class, English-speaking, mother–child dyads were recorded in a naturalistic context at home during play and eating activities. Explicit and implicit feedback were different in terms of the proportion of responses available to the child and their relation to well-formed and ill-formed utterances. The style of response was similar for most analyses across the four mothers.

The function of motherese has become a pivotal issue in the language-learning literature. The current research takes the approach of asking whether the prosodic characteristics that are distinctive to motherese could play a special role in facilitating the acquisition of syntax. Hirsh-Pasek, Kemler Nelson, Jusczyk, Cassidy, Druss & Kennedy (1987) showed that infants aged 0;7–0;10 are sensitive to prosodic cues that would help them segment the speech stream into perceptual units that correspond to clauses. The present study shows that infants' sensitivity to segment-marking cues in ongoing speech holds for motherese but not for adult-directed speech. The finding is that, for motherese only, infants orient longer to speech that has been interrupted at clausal boundaries than to matched speech that has been interrupted at within-clause locations. This selective preference indicates that the prosodie qualities of motherese provide infants with cues to units of speech that correspond to grammatical units of language – a potentially fundamental contribution of motherese to the learning of syntax.

This study investigated whether crosslinguistic interference occurs in the domain of subject realization in Spanish in a bilingual acquisition context. We were also interested in exploring whether the source of the interference is due to child-internal crosslanguage contact between English and Spanish, as is commonly assumed, or due to the nature of the language input in a bilingual family, a factor which has not typically been considered in studies of crosslinguistic influence. The use of subjects in a null subject language like Spanish is a phenomenon linked to the pragmatics/syntax interface of the grammar, and thus, is a domain where crosslinguistic interference is predicted to be likely to occur in bilingual acquisition (Müller & Hulk, 2001). Using spontaneous language data available from CHILDES (www.childes.psy.cmu.edu), we examined the use of overt subjects in Spanish by two Spanish monolingual children (ages: 1;8–2;7 and 1;8–1;11) one Spanish–English bilingual child (age 1;9–2;6) and their parental interlocutors. We looked at the proportions of overt versus null subjects as well as the discourse-pragmatic contexts of overt subject use by the children in order to uncover bilingual/monolingual differences in the distributional properties and the functional determinants of subject realization. We also looked at identical variables in the speech of the children's parental interlocutors to investigate the potential influence of the input on the children's output. Our results suggest that the bilingual child showed patterns in her subject realizations in Spanish that could be interpreted as due to crosslinguistic effects from English; however, there is also evidence that these effects may have a source in the input, rather than resulting from internal crosslanguage contact. While our data do not permit us to distinguish conclusively between these two possible sources, they indicate that future research on crosslinguistic influence in bilingual acquisition should take input into account.