Thai has imperfective aspectual morphemes that are not obligatory in usage, whereas English has obligatory grammaticized imperfective aspectual marking on the verb. Furthermore, Thai has verb final deictic-path verbs that form a closed class set. The current study investigated if obligatoriness of these grammatical categories in Thai and English affects the expression of co-occurring temporal events and actions depicted in three different short animations. Ten children aged four years, five years, six years and seven years, and ten adults as a comparison group from each of the two languages participated. English speakers explicitly expressed the ongoingness of the events more than Thai speakers, whereas Thai speakers expressed the entrance and exit of protagonists depicted in the animations significantly more than English speakers. These results support the notion that obligatory grammatical categories shape how Thai and English speakers express temporal events or actions.

This commentary concerns two issues: the contribution of connectionism and theories of learning to developmental psychology; and the status of connectionist models of syntax acquisition.

Since there are no systematic pauses delimiting words in speech, the problem of word segmentation is formidable even for monolingual infants. We use computational modeling to assess whether word segmentation is substantially harder in a bilingual than a monolingual setting. Seven algorithms representing different cognitive approaches to segmentation are applied to transcriptions of naturalistic input to young children, carefully processed to generate perfectly matched monolingual and bilingual corpora. We vary the overlap in phonology and lexicon experienced by modeling exposure to languages that are more similar (Catalan and Spanish) or more different (English and Spanish). We find that the greatest variation in performance is due to different segmentation algorithms and the second greatest to language, with bilingualism having effects that are smaller than both algorithm and language effects. Implications of these computational results for experimental and modeling approaches to language acquisition are discussed.

From early on, infants show a preference for infant-directed speech (IDS) over adult-directed speech (ADS), and exposure to IDS has been correlated with language outcome measures such as vocabulary. The present multi-laboratory study explores this issue by investigating whether there is a link between early preference for IDS and later vocabulary size. Infants’ preference for IDS was tested as part of the ManyBabies 1 project, and follow-up CDI data were collected from a subsample of this dataset at 18 and 24 months. A total of 341 (18 months) and 327 (24 months) infants were tested across 21 laboratories. In neither preregistered analyses with North American and UK English, nor exploratory analyses with a larger sample did we find evidence for a relation between IDS preference and later vocabulary. We discuss implications of this finding in light of recent work suggesting that IDS preference measured in the laboratory has low test-retest reliability.

Mean Length of Utterance (MLU) has been widely used to measure children’s early language development in a variety of languages. This study investigates the utility of MLU to measure language development in four agglutinative and morphologically complex Southern Bantu languages. Using a variant of MLU, MLU3, based on the three longest sentences children produced, we analysed the utterances of 448 toddlers (16-32 months) collected using the MacArthur-Bates Communicative Development Inventory, a parent-report tool. MLU3, measured in words (MLU3-w) and morphemes (MLU3-m), significantly correlated with age and other indices of language growth (e.g., grammar and vocabulary). MLU3 measures also accounted for significant variance in language development particular morphosyntactic development. Our results suggest that MLU3-m is a more sensitive measure than MLU3-w. We conclude that MLU measured in morphemes provides a useful addition to other indices of language development in these kinds of morphologically complex languages.

The present study tested Huttenlocher & Weiner's (1971) hypothesis concerning the role of grammatical function in sentence comprehension. Children arranged objects to correspond to descriptions of transitive relations in two tasks. The patterns of object placements provided evidence of how children understood the various sentence forms. Contrary to Huttenlocher & Weiner's hypothesis, grammatical function was not a critical factor in object placements. This was true based on the group data or individual-based analyses. Two factors were important: logical function and order of mention of the items in the sentence. Whether an item was grammatical subject or grammatical object did not affect subjects' choices. The order of mention effects resulted from inattention to sentence meaning prior to the initial choices on certain trials. If the logical relations in a sentence were understood prior to the response, only logical function influenced subjects' responses.

The Yucatec Maya language has a highly complex deictic system with interesting typological differences that in addition to demonstratives and locative adverbs also includes ostensive evidentials and modal adverbs. Given that deictic words are among the first that children produce, the aim of this study is to identify the early acquisition that Yucatec Mayan children follow to map out each deictic form. Deictic words taken from spontaneous, longitudinal, transversal corpora and Gaskins's (1990) field work annotations were labeled and analyzed. The results show that children begin by uttering protoforms mapped with prototypical functions of locative and modal adverbs, but the functions of both demonstratives and ostensive evidentials are expressed mostly with the same protoform, which is similar to the deictic organizations of other languages. When children become productive, they overextend functions, which demonstrates a reanalysis of the system before acquisition is complete.

We examined full-term and preterm infants’ perception of frequent and infrequent phonotactic pairings involving sibilants and liquids. Infants were tested on their preference for syllables with onsets involving /s/ or /ʃ/ followed by /l/ or /r/ using the Headturn Preference Procedure. Full-term infants preferred the frequent to the infrequent phonotactic pairings at 9 months, but not at either younger or older ages. Evidence was inconclusive regarding a possible difference between full-term and preterm samples; however, limitations on the preterm sample size limited our power to detect differences. Preference for the frequent pairing was not related to later vocabulary development.

MacWhinney's list of proposed mechanisms for language acquisition seems so all-encompassing that it might appear churlish to dwell on a mechanism that's left out, but on his ultimate list of critical mechanisms there is an indeed an important (and intended) omission: innate, linguistically-specialized constraints. Such constraints are indeed mentioned, but if I understand the point of the article correctly, it is to argue that seven cognitive mechanisms, ranging from competition to cue construction, indirect negative evidence and monitoring, collectively obviate the need for any innate machinery that it specialized for language. Why not include room for innate, domain-specific constraints, too?