Six children were visited in their homes every two weeks for 18 months from the age of six months in order to observe their developing comprehension and production of words. Controlled testing of the children's developing vocabulary was also carried out to provide a more detailed picture of the precise context in which a word was understood or produced. The results showed both similarities and individual differences among the children in patterns of early comprehension. For all six children there was a very close relationship between early production and comprehension of words: words that were contextually flexible in production tended also to be so in comprehension and words that were context-bound also tended to be so in both modalities although there was some evidence that the two types of word differed in the extent to which comprehension preceded production. All children were also similar in showing evidence of contextually flexible comprehension very early on. However, there were individual differences both in the rate at which comprehension developed and in the lag between comprehension and production. The significance of this pattern of development for accounts of lexical development is explored.

The development of two children's responses to yes/no questions is studied longitudinally. It will be proposed that the children realize that they must verbalize, but do not understand the semantics of the question form or the affirmative and negative particles. Their answers are not appropriate by the conventions of adult speech. In this situation, each child develops his own system, a phenomenon to be called PRAGMATIC VARIATION. Head nodding and shaking show a pattern of development comparable to that of the verbal responses. The options available to children acquiring English are discussed.

Comparison of patterns of cluster realization from 47 children ranging in age from 3;4 to 6;8 with functional (non-organic) speech disorders with those reported in the literature for normal acquisition reveals that these patterns are essentially the same for both groups. Using a two-level generative phonology for children's independent systems, further analysis of cluster realizations by means of feature geometry and under-specification theory reveals that there are systematic and principled relationships between adult representations of clusters and children's underlying representations and between children's underlying representations and their phonetic representations. With special emphasis on coalescence phenomena, it is suggested that the apparent diversity in children's cluster realizations can be reduced to four constraints on the form of underlying and phonetic representations.

The present study examines adult and child word-initial voice onset time productions in English and Hindi (10 adults and 20 children in each language) to determine the age of acquisition of the phonemic voice contrast. Cross-linguistic differences in patterns of acquisition were found, but these need not be traced to the different phonological Systems per se. An examination of the data indicates that the best predictor of age of voice contrast acquisition across languages is one which rests on the actual acoustic differences between members of phonologically contrastive pairs. In general it was found that the larger the post-release voice onset time differences between pair members in the adult model, the earlier the contrast is reliably produced by child language learners.

The data obtained in two investigations (one a longitudinal/cross-sectional naturalistic study, the other a quasi-experimental study) demonstrate that preschool age children have the capacity for hypothetical reference. However, the data also indicate that this capacity for hypothetical reference operates within certain constraints, particularly early in the preschool years. Specifically, future hypothetical reference is an earlier acquisition than past hypothetical reference; reference to single hypothetical events appears sometime prior to reference to sequences of hypothetical events; and accuracy is better in self-initiated than other-initiated hypothetical reference. The implications of these findings are discussed.

Infants' sensitivity to word units in fluent speech was examined by inserting 1 sec pauses either at boundaries between successive words (Coincident versions) or between syllables within words (Noncoincident versions). In Experiment 1, 24 11-month-olds listened significantly longer to the Coincident versions. In Experiment 2, 24 four-and-a-half-and 24 nine-month-olds did not exhibit the preference for the Coincident versions that the 11-month-olds showed. When the stimuli were low-pass filtered in Experiment 3, 24 11-month-olds showed no preference for the Coincident versions, suggesting they rely on more than prosodic cues. New stimulus materials in Experiment 4 indicated that responses by 24 11-month-olds to the Coincident and Noncoindent versions did not depend solely on prior familiarity with the targets. Two groups of 30 11-month-olds tested in Experiment 5 were as sensitive to boundaries for Strong/Weak words as for Weak/Strong words. Taken together, the results suggest that, by 11 months, infants are sensitive to word boundaries in fluent speech, and that this sensitivity depends on more than just prosodic information or prior knowledge of the words.

Word learning by young children is viewed as a problem of deriving meaning from the use of forms in discourse contexts. Uses of causal and temporal terms in private speech by a child studied longitudinally from 1;9 to 3;0 are analysed from this perspective. Evidence is presented that words are first constrained to uses in specific discourse contexts, and later used more flexibly and with greater control over the semantics of the terms. Derivation of meaning from discourse is described as a dialectical process, and as such it is claimed to be more consistent with the full range of observational data, and with theories of word learning applicable to older children and adults, than other current theories of lexical acquisition in early childhood.

Pronoun case errors, or overextensions, like *me want it are characteristic of English child language. This paper explores a hypothesis that the morphological structure of a pronoun influences the pattern of these errors. The Language Acquisition Device (LAD) attempts to analyse English pronoun case forms into stems and affixes, but cannot because of their irregularity. Nevertheless the LAD extracts a phonetic core for each pronoun (e.g. /m-/ for the ist sg., /h-/ for the 3rd masc. sg.). The phonetic core blocks the overextension of suppletive nominative forms like I and she. This hypothesis predicts strong differences in the frequency and types of errors between pronouns with suppletive nominatives and those without. Evidence for this hypothesis was found in a transcript database of twelve children, with data collected in one hour samples every month from 1;0 to 3;0. 20,908 pronouns were examined, 1347 of which were errors. Statistical analyses of these data provide support for this hypothesis.

This study investigates whether number dissimilarities on subject and object DPs facilitate the comprehension of subject- and object-extracted centre-embedded relative clauses in children with Grammatical Specific Language Impairment (G-SLI). We compared the performance of a group of English-speaking children with G-SLI (mean age: 12;11) with that of two groups of younger typically developing (TD) children, matched on grammar and receptive vocabulary, respectively. All groups were more accurate on subject-extracted relative clauses than object-extracted ones and, crucially, they all showed greater accuracy for sentences with dissimilar number features (i.e., one singular, one plural) on the head noun and the embedded DP. These findings are interpreted in the light of current psycholinguistic models of sentence comprehension in TD children and provide further insight into the linguistic nature of G-SLI.

In order to understand how language abilities emerge in typically and atypically developing infants and toddlers, it is important to embrace complexity in development. In this paper, we describe evidence that early language development is an experience-dependent process, shaped by diverse, interconnected, interdependent developmental mechanisms, processes, and abilities (e.g. statistical learning, sampling, functional specialization, visual attention, social interaction, motor ability). We also present evidence from our studies on neurodevelopmental disorders (e.g. Down syndrome, fragile X syndrome, Williams syndrome) that variations in these factors significantly contribute to language delay. Finally, we discuss how embracing complexity, which involves integrating data from different domains and levels of description across developmental time, may lead to a better understanding of language development and, critically, lead to more effective interventions for cases when language develops atypically.

Following the proposal that consonants are more involved than vowels in coding the lexicon (Nespor, Peña & Mehler, 2003), an early lexical consonant bias was found from age 1;2 in French but an equal sensitivity to consonants and vowels from 1;0 to 2;0 in English. As different tasks were used in French and English, we sought to clarify this ambiguity by using an interactive word-learning study similar to that used in French, with British-English-learning toddlers aged 1;4 and 1;11. Children were taught two CVC labels differing on either a consonant or vowel and tested on their pairing of a third object named with one of the previously taught labels, or part of them. In concert with previous research on British-English toddlers, our results provided no evidence of a general consonant bias. The language-specific mechanisms explaining the differential status for consonants and vowels in lexical development are discussed.

Early language comprehension may be one of the most important predictors of developmental risk. The need for performance-based assessment is predicated on limitations identified in the exclusive use of parent report and on the need for a performance measure with which to assess the convergent validity of parent report of comprehension. Child performance data require the development of procedures to facilitate infant attention and compliance. Forty infants (20 at 1 ; 4 and 20 at 1 ; 8) acquiring English completed a standard picture book task and the same task was administered on a touch-sensitive screen. The computerized task significantly improved task attention, compliance and performance. Reliability was high, indicating that infants were not responding randomly. Convergent validity with parent report and 4-month stability was substantial. Preliminary data extending this approach to Mexican-Spanish are presented. Results are discussed in terms of the promise of this technique for clinical and research settings and the potential influences of cultural factors on performance.

In this paper we discuss a computational cognitive model of children's poor performance on pronoun interpretation (the so-called Delay of Principle B Effect, or DPBE). This cognitive model is based on a theoretical account that attributes the DPBE to children's inability as hearers to also take into account the speaker's perspective. The cognitive model predicts that child hearers are unable to do so because their speed of linguistic processing is too limited to perform this second step in interpretation. We tested this hypothesis empirically in a psycholinguistic study, in which we slowed down the speech rate to give children more time for interpretation, and in a computational simulation study. The results of the two studies confirm the predictions of our model. Moreover, these studies show that embedding a theory of linguistic competence in a cognitive architecture allows for the generation of detailed and testable predictions with respect to linguistic performance.

An investigation into the pronoun distribution of a pronoun-reversing child reveals inconsistencies both within production and between production and comprehension. This distribution is compatible with some analyses of normal pronoun development and pronoun reversal which have attributed non-adult person distinctions to the child. However, the data are also compatible with a quite distinct hypothesis which postulates that the child's pronouns are plurifunctional: the unreversed pronouns encode full adult distinctions, and are independent of the reversed pronouns, which function to shift perspective. The evaluation of these hypotheses and the questions they raise for normal and pathological pronoun development are discussed.

We examined code-switching (CS) in the speech of twenty-four bilingual caregivers when speaking with their 18- to 24-month-old children. All parents CS at least once in a short play session, and some code-switched quite often (over 1/3 of utterances). This CS included both inter-sentential and intra-sentential switches, suggesting that at least some children are frequently exposed to mixed-language sentences. However, we found no evidence that this exposure to CS had any detrimental effect on children's word learning: children's overall vocabulary size did not relate to parental inter-sentential CS behavior, and was positively related to within-sentence CS. Parents often repeated words across their two languages, but this did not appear to increase the likelihood of children having translation equivalents in their vocabulary. In short, parents appear to CS fairly often to young children, even within sentences, but there is no evidence that this delays child lexical acquisition.

This study examined the evolution of visual perspective-taking skills in relation to the comprehension and production of first, second and third person pronouns. Twelve French-speaking and 12 English-speaking children were observed longitudinally from 1;6 until they had acquired all pronouns and succeeded on all tasks. Free-play sessions and three tasks were used to test pronominal competence. Four other tasks assessed Level-1 perspective-taking skills: two of these tasks required the capacity to consider two visual perspectives, and two others tested the capacity to coordinate three such perspectives. The results indicated that children's performance on perspective-taking tasks was correlated with full pronoun acquisition. Moreover, competence at coordinating two visual perspectives preceded the full mastery of first and second person pronouns, and competence at coordinating three perspectives preceded the full mastery of third person pronouns when a strict criterion was adopted. However, with less stringent criteria, the sequence from perspective taking to pronoun acquisition varied either slightly or considerably. These findings are discussed in the light of the ‘specificity hypothesis’ concerning the links between cognition and language, and also in the context of the recent body of research on the child's developing theory of mind.

In Harris, Barrett, Jones & Brookes (1988), we reported the results of a detailed analysis of the initial uses of the first 10 words which were produced by four children. The present paper reports the results of an analysis of the subsequent uses of these 40 words. This analysis reveals that seven qualitatively different patterns of change occurred between the children's initial and subsequent uses of these words; the particular patterns of change which occurred support Barrett's (1986) model of early lexical development. In addition, it was found that, although there was a strong relationship between maternal speech and the children's initial word uses, the relationship between maternal speech and the children's subsequent word uses was very much weaker. These findings indicate that the role of linguistic input in early lexical development may decline quite sharply once the child has established initial uses for words.

Fourteen two-year-olds (M=2; o) were presented with minimal word pairs in a new and highly efficient experimental perception paradigm. The data provide a preliminary view of the relative difficulty of various minimal phonological contrasts for children. The study specifically focuses on perception of some phonological contrasts which usually are actualized and some which usually are not actualized in two-year-old child productions. The data suggest that perceptual difficulties probably play a substantial role in some childhood speech errors, but little, if any, role in others.

This study measured longitudinal change in six parameters of infant utterances (i.e. number of sounds, CV syllables, supraglottal consonants, and repetitions per utterance, temporal duration, and seconds per sound), investigated previously unexplored characteristics of repetition (i.e. number of vowel and CV syllable repetitions per utterance) and analyzed change in vocalizations in relation to age and developmental milestones using multilevel models. Infants (N=18) were videotaped bimonthly during naturalistic and semi-structured activities between 0 ; 3 and the onset of word use (M=11·8 months). Results showed that infant utterances changed in predictable ways both in relation to age and in relation to language milestones (i.e. reduplicated babble onset, word comprehension and word production). Looking at change in relation to the milestones of language development led to new views of babbling, the transition from babbling to first words, and processes that may underlie these transitions.

The objectives were to explore the often reported noun advantage in children's language acquisition using a picture naming paradigm and to explore the variables that affect picture naming performance. Participants in Experiment 1 were aged three and five years, and in Experiment 2, five years. The stimuli were action and object pictures. In Experiment 1, action pictures produced more errors than object pictures for the three-year-olds, but not the five-year-olds. A qualitative analysis of the errors revealed a somewhat different pattern of errors across age groups. In Experiment 2 there was no robust difference in accuracy for the actions and objects but naming times were longer for actions. Across both experiments, imageability was a robust predictor of object naming performance, while spoken frequency was the most important predictor of action naming. The results are discussed in terms of possible differences in the manner in which nouns and verbs are acquired.