Because most common words have multiple meanings,children are often learning new senses of existing words,rather than entirely new words. Here, we explore whetherchildren can use their knowledge of an existing word sense toconstrain their interpretation of a new word meaning. Acrosstwo studies, we teach 3- and 4-year-olds and adults novelwords for materials, and manipulate whether those words arealso used flexibly, to label objects made from those materials.We find that participants of all ages assign markedly differentinterpretations to the object labels when they have a prior,material meaning: Rather than extending them to otherobjects of similar shapes, they extend them on the basis ofshared material, thus overriding the well-documented shapebias. These findings suggest that language learners can use aword’s prior meaning to learn about the structure of its newmeaning.

Whereas adults exchange conversational turns very rapidly, children often respond after long gaps. However, it hasbeen proposed that the infrastructure necessary to take turns develops in infancy. Why are children slow to respond to turns?Adults’ turn-taking skills, it has been argued, rely on an ability to both predict when the current turn will end and prepare aresponse as soon as possible. In two experiments, we ask how these two abilities (prediction and early preparation) develop.Adults and 3-to-5-year-olds answered yes/no questions while playing an iPad-based maze game. Distributional analysis ofanswer latencies suggest that (i) neither children nor adults rely on fine-grained predictions of turn duration and (ii) bothchildren and adults use predictions about turn content to prepare their answer early. In sum, by the age of three, childrenalready have the cognitive architecture necessary to take turns successfully. ,

Many words have multiple yet predictably related meanings. For example, in English and in other languages, the sameroot morphemes can be used flexibly, to label an action and the instrument used to perform the action (e.g., we hammerwith a hammer and mix with a mixer). Previous findings indicate that four- and five-year-olds have formed abstractgeneralizations about these patterns and use them to infer new word meanings, such that they expect a word that haslabeled an action to also label its instrument. But how do these generalizations develop? Across five experiments witha large sample of English-speaking children, we show that in the third year of life, children begin to generalize wordsbetween actions and instruments: e.g., they expect that if an action involving an instrument and patient has been calledpabbing, then a pab (or a pabber) will refer to the instrument. Additionally, we find that children of the same age alsospontaneously extend words between actions and instruments: e.g., if an action has been called pabbing, children indicatethat the instrument cannot be a neefoo, presumably because they think it should instead be called a pab or a pabber.Critically, we show that these results do not depend on whether the new word labels an event for which children knowa word (e.g., hammering) or instead labels a novel event involving a novel instrument. These findings suggest that byage three, children’s knowledge of lexical flexibility is generative and abstract, and may not be constructed through item-specific learning.

What is the mechanism by which linguistic knowledge is updated over time? In six experiments, we asked whether error-driven learning can explain how adults and children add new words to their vocabulary. Participants were exposed tonovel object labels that were more or less unexpected given participants linguistic knowledge. Two-to-four-year-olds werestrongly affected by expectations based on contextual constraint when choosing the referent of a new label. However,while adults formed stronger memory traces for novel words that violated a stronger prior expectation, childrens memorywas unaffected by the strength of their prior expectations. We conclude that the encoding of new words in memory followsthe principles of error-driven learning in adults, but not in preschoolers.

Research in lexical acquisition has frequently focused on children's ability to make rapid, context-informed guesses about the meaning of newly encountered words, known as ‘fast mapping'. However, there is a gap in research examining how children and adults revise and adjust these guesses about word meanings as they encounter words repeatedly applied to different referents. We propose, on computational grounds, that learners adjust word meanings incrementally to accommodate new evidence. To begin to test this proposal, we lay out a new research program probing how word meanings evolve. In a pilot experiment, adults learn the meaning of novel kinship terms and we probe their beliefs by repeatedly eliciting generalizations. We manipulate the order in which participants observe the same word used to refer to different members of a family tree. We find a mixed pattern of order effects but our inspection of individual trajectories suggestive of a syntax-level relationship between the current and previous hypothesis. This relationship was supported by a computational model based analysis of lexical meaning generation via a probabilistic language of thought.

In natural languages and in experimental studies of artificial language learning, case marking of grammatical arguments is more likely to be used in languages with flexible word order due to an efficiency trade-off between production effort and communicative accuracy. However, experimental evidence suggests that language learners are less efficient when there is a social bias in favour of a group whose productions are inefficient. Here, we examine the impact of autistic traits on efficient communication. We find that autistic people's use of case in the absence of a social bias is comparative to their neurotypical peers. However, we also find evidence that autistic people adhere more to social biases; they increase production effort in order to behave more like the group they are biased towards. We argue that some autistic people may be more likely to adhere to a social bias as a result of learnt social behaviours. More generally, these results underscore the importance of studying more diverse populations in language evolution research.

Morphological paradigms differ widely across languages in their size and number of contrasts they mark. Recent work onmorphological complexity has argued that certain features of even very large paradigms make them easy to learn and use.Specifically, Ackerman & Malouf, 2013 propose an information-theoretic measure, i-complexity, which captures the extentto which forms in the paradigm predict each other, and show that languages which differ widely in surface complexityexhibit similar i-complexity; in other words, paradigms with many contrasts reduce the learnability challenge for learnersby having predictive relationships between inflections. We present three artificial language learning experiments testingwhether i-complexity in fact predicts learnability of nominal paradigms where nouns inflect for class and number. Ourresults reveal only weak evidence that paradigms with low i-complexity are easier to learn than paradigms with highi-complexity. We suggest that alternative aspects of complexity may have a larger impact on learning.

Because words have multiple meanings, language users must often choose appropriate meanings according to the context of use. How this potential ambiguity affects first language learning, especially word learning, is unknown. Here, we present the first large-scale study of how children are exposed to, and themselves use, ambiguous words in their language learning environments. We tag 180,000 words in two longitudinal child language corpora with word senses from WordNet, focusing between 9 and 51 months and limiting to words from a popular parental vocabulary report. We then compare the diversity of sense usage in adult speech around children to that observed in a sample of adult language, as well as the diversity of sense usage in children's own productions. To accomplish this we use a Bayesian model-based estimate of sense entropy, a measure of diversity that takes into account uncertainty inherent in small sample sizes. This reveals that sense diversity in caregivers' speech to children is similar to that observed in a sample of adult-directed written material, and that children's use of nouns---but not verbs---is similarly diverse to that of adults. Finally, we show that sense entropy is a significant predictor of vocabulary development: children begin to produce words with a higher diversity of adult sense usage at later ages. We discuss the implications of our findings for theories of word learning.

Psychological scientists have become increasingly concerned with issues related to methodology and replicability, and infancy researchers in particular face specific challenges related to replicability: For example, high-powered studies are difficult to conduct, testing conditions vary across labs, and different labs have access to different infant populations. Addressing these concerns, we report on a large-scale, multisite study aimed at (a) assessing the overall replicability of a single theoretically important phenomenon and (b) examining methodological, cultural, and developmental moderators. We focus on infants’ preference for infant-directed speech (IDS) over adult-directed speech (ADS). Stimuli of mothers speaking to their infants and to an adult in North American English were created using seminaturalistic laboratory-based audio recordings. Infants’ relative preference for IDS and ADS was assessed across 67 laboratories in North America, Europe, Australia, and Asia using the three common methods for measuring infants’ discrimination (head-turn preference, central fixation, and eye tracking). The overall meta-analytic effect size (Cohen’s d) was 0.35, 95% confidence interval = [0.29, 0.42], which was reliably above zero but smaller than the meta-analytic mean computed from previous literature (0.67). The IDS preference was significantly stronger in older children, in those children for whom the stimuli matched their native language and dialect, and in data from labs using the head-turn preference procedure. Together, these findings replicate the IDS preference but suggest that its magnitude is modulated by development, native-language experience, and testing procedure.