This longitudinal study assessed three acoustic components of maternal infant-directed speech (IDS) – pitch, affect, and vowel hyperarticulation – in relation to infants’ age and their expressive vocabulary size. These three individual components were measured in IDS addressed to infants at 7, 9, 11, 15, and 19 months (N = 18). All three components were exaggerated at all ages in mothers’ IDS compared to their adult-directed speech. Importantly, the only significant predictor of infants’ expressive vocabulary size at 15 and 19 months was vowel hyperarticulation, but only at 9 months and beyond, not at 7 months, and not pitch or affect at any age. These results set apart vowel hyperarticulation in IDS to infants as the critical IDS component for vocabulary development. Thus IDS, specifically the degree of vowel hyperarticulation therein, is a vehicle by which parents can provide the most optimal speech quality for their infants’ linguistic and communicative development.

Children tend to regularize their productions when exposed to artificial languages, an advantageous response to unpredictable variation. But generalizations in natural languages are typically conditioned by factors that children ultimately learn. In two experiments, adult and six-year-old learners witnessed two novel classifiers, probabilistically conditioned by semantics. Whereas adults displayed high accuracy in their productions – applying the semantic criteria to familiar and novel items – children were oblivious to the semantic conditioning. Instead, children regularized their productions, over-relying on only one classifier. However, in a two-alternative forced-choice task, children's performance revealed greater respect for the system's complexity: they selected both classifiers equally, without bias toward one or the other, and displayed better accuracy on familiar items. Given that natural languages are conditioned by multiple factors that children successfully learn, we suggest that their tendency to simplify in production stems from retrieval difficulty when a complex system has not yet been fully learned.

Vocabulary input frequency influences age of acquisition, and is also an essential control for investigating the influence of other factors. We propose a new method of frequency estimation, self-report. 918 Danish-speaking parents of 12–36-month-old children estimated their frequency of use of 725 words. Self-report was substantially correlated with both language sample based frequencies (0.67) and frequencies of a large written corpus of Danish (0.58). Correlations within vocabulary categories between frequency and age of acquisition, restricted to words occurring in the language samples, were comparable for the two estimates. Overall, self-report based frequency estimates appear to have a promising degree of validity, which reflects their greatest strength, independence of the situation.

This study compared the temporal measurements of stop consonants in 29 three- to six-year-old Mandarin-speaking children and 12 Mandarin-speaking adults. Each participant produced 18 Mandarin disyllabic words which contained six stop consonants /p, pʰ, t, tʰ, k, kʰ/ each followed by three vowels /a, i, u/ at the word-initial position in the first syllable. The temporal measurements of VOT, overall burst duration, average duration per burst, number of bursts, and VOT-lag duration were obtained. Although adult-like short-lag VOTs were achieved in all children, the long-lag VOTs were widespread in the younger group and gradually developed to a concentrated distribution in the older children. Further analysis of the burst and VOT-lag revealed that these children tended to produce shorter average duration per burst and longer VOT-lag than the adults. These results indicate that children in this age range may not have developed adult-like laryngeal–oral timing pattern and airflow control for stop production.

Children's ability to refer is underpinned by their developing cognitive skills. Using a production task (n = 57), we examined pre-articulatory visual fixations to contrast objects (e.g., to a large apple when the target was a small one) to investigate how visual scanning drives informativeness across development. Eye-movements reveal that although four-year-olds fixate contrast objects to a similar extent as seven-year-olds and adults, this does not result in explicit referential informativeness. Instead, four-year-olds frequently omit distinguishing information from their referring expressions regardless of the comprehensiveness of their visual scan. In contrast, older children make greater use of information gleaned from their visual inspections, like adults. Thus, we find a barrier not to the incidence of contrast fixations by younger children, but to their use of them in referential informativeness. We recommend that follow-up work investigates whether younger children's immature executive skills prevent them from describing referents in relation to contrast objects.

This study tested the claim of input-based accounts of language acquisition that children's inflectional errors reflect competition between different forms of the same verb in memory. In order to distinguish this claim from the claim that inflectional errors reflect the use of a morphosyntactic default, we focused on the Japanese verb system, which shows substantial by-verb variation in the frequency distribution of past and nonpast forms. 22 children aged 3;2–5;8 (Study 1) and 26 children aged 2;7–4;11 (Study 2) completed elicited production studies designed to elicit past and nonpast forms of 20 verbs (past-biased and nonpast-biased). Children made errors in both directions, using past forms in nonpast contexts, and vice versa, with the likelihood of each determined by the frequency bias of the two forms in the input language, even after controlling for telicity. This bi-directional pattern provides particularly direct evidence for the role of frequency-sensitive competition between stored forms.

Studies examining productive syntax have used varying elicitation methods and have tended to focus on either young children or adolescents/adults, so we lack an account of syntactic development throughout middle childhood. We describe here the results of an analysis of clause complexity in narratives produced by 354 speakers aged from four years to adulthood using the Expressive, Receptive, and Recall of Narrative Instrument (ERRNI). We show that the number of clauses per utterance increased steadily through this age range. However, the distribution of clause types depended on which of two stories was narrated, even though both stories were designed to have a similar story structure. In addition, clausal complexity was remarkably similar regardless of whether the speaker described a narrative from pictures, or whether the same narrative was recalled from memory. Finally, our findings with the youngest children showed that the task of generating a narrative from pictures may underestimate syntactic competence in those aged below five years.

During the first two years of life, infants concurrently refine native-language speech categories and word learning skills. However, in the Switch Task, 14-month-olds do not detect minimal contrasts in a novel object–word pairing (Stager & Werker, 1997). We investigate whether presenting infants with acoustically salient contrasts (liquids) facilitates success in the Switch Task. The first two experiments demonstrate that acoustic differences boost infants’ detection of contrasts. However, infants cannot detect the contrast when the segments are digitally shortened. Thus, not all minimal contrasts are equally difficult, and the acoustic properties of a contrast matter in word learning.

We analyzed the conversational corpora of two German and two English children to investigate how the different use types of the adversative connectives aber and but influence the probability of monologically versus dialogically constructed utterances in the first year of use. Our findings show that children produce adversative connectives mainly in dialogic structures for illocutionary and theme-management purposes, but that the use types of adversative connectives lead to a different distribution of monologic and dialogic clause combinations. The results suggest that monologic and dialogic realizations as a function of text type must be considered when describing the developmental trajectory of the different use types of adversative connectives.

Finnish is a language with simple syllable structure but rich morphology. It was investigated whether syllables or morphemes are preferred processing units in early reading. To this end, Finnish first- and second-grade children read sentences with embedded inflected target words while their eye-movements were registered. The target words were either in essive or inessive/adessive (i.e., locative) case. The target words were either non-hyphenated, or had syllable-congruent or syllable-incongruent hyphenation. For the locatives, the syllable-incongruent hyphenation coincided with the morpheme boundary, but this was not the case for the essives. It was shown that the second-graders were slowed down by hyphenation to a larger extent than first-graders. However, there was no slowdown in gaze duration for either age group when the syllable-incongruent hyphen was morpheme-congruent. These findings suggest that Finnish readers already utilize morpheme-level information during the first grade.