Purpose: Two-year-olds produce third person singular –smore accurately on verbs in sentence-final position as compared with verbs in sentence-medial position. This study was designed to determine whether these sentence-position effects can be explained by perceptual factors.Method: For this purpose, the authors compared 22- and 27-month-olds' perception and elicited production of third person singular –sin sentence-medial versus-final position. The authors assessed perception by measuring looking/listening times to a 1-screen display of a cartoon paired with a grammatical versus an ungrammatical sentence (e.g.,Sheeatsnowvs.Sheeatnow).Results: Children at both ages demonstrated sensitivity to the presence/absence of this inflectional morpheme in sentence-final, but not sentence-medial, position. Children were also more accurate at producing third person singular –ssentence finally, and production accuracy was predicted by vocabulary measures as well as by performance on the perception task.Conclusions: These results indicate that children’s more accurate production of third person singular–sin sentence-final position cannot be explained by articulatory factors alone but that perceptual factors play an important role in accounting for early patterns of production. The findings also indicate that perception and production of inflectional morphemes may be more closely related than previously thought.

We evaluated the impact of exposure to a second language on infants’ emerging speech production skills. We compared speech produced by three groups of 12-month-old infants while they interacted with interlocutors who spoke to them in Spanish and English: monolingual English-learning infants who had previously received 5 hours of exposure to a second language (Spanish), English- and Spanish-learning simultaneous bilinguals, and monolingual English-learning infants without any exposure to Spanish. Our results showed that the monolingual English-learning infants with short-term exposure to Spanish and the bilingual infants, but not the monolingual English-learning infants without exposure to Spanish, flexibly matched the prosody of their babbling to that of a Spanish- or English-speaking interlocutor. Our findings demonstrate the nature and extent of benefits for language learning from early exposure to two languages. We discuss the implications of these findings for language organization in infants learning two languages.

We used Bayesian modeling to aggregate experiments investigating infants' sensitivity to native language phonotactics. Our findings were based on data from 83 experiments on about 2000 infants learning 8 languages, tested using 4 different methods. Our results showed that, unlike with artificial languages, infants do exhibit sensitivity to native language phonotactic patterns in a lab setting. However, the exact developmental trajectory depends on the phonotactic pattern being tested. Before 8 months, infants tuned into non-local dependencies between vowels: specifically, vowel harmony. Between 8- and 10-months, infants demonstrated a consistent sensitivity to both local dependencies and non-local consonant dependencies. Sensitivity to non-local vowel dependencies that are not based on harmony emerged only after 10-months. These findings provide a benchmark for future experimental and computational research on the acquisition of phonotactics.