Valentine Hacquard - US grants

This project investigates how children come to learn the meaning of verbs that describe mental states such a "think" or "want". Such verbs are important for several reasons: first, unlike action verbs like "run," they describe internal states that are not easily observable. Second, such verbs have often been used as a window into children's understanding of other people's minds. Children seem to make consistent mistakes in their understanding of verbs like "think". This is often taken to reflect an initial inability to attribute mental states (such as beliefs) to others (so-called 'theory of mind'). However, our understanding of children's linguistic representation of mental verbs at various stages of development is lacking in important ways. Yet, such an understanding is crucial before causal claims can be made about the connection between language and theory of mind. Several factors could be responsible for children's linguistic mistakes. In particular, we explore the hypothesis that the difficulty children experience with these verbs is neither conceptual, nor grammatical in nature, but derives from mastering how these verbs are used in conversation.

One of the central aims of this research is to develop tools for determining whether success or failure in some linguistic task is driven by grammatical knowledge or the reasoning associated with using this knowledge. Consequently, this research will have clear implications for language delay, and disorders of language and cognition, such as Autism. In addition, this project will provide funding and research experience to graduate and undergraduate students. Graduate students working on the project will serve as near-peer mentors to the undergraduate students. This arrangement provides graduate students with mentoring experience, better preparing them for research positions, and providing a model for graduate training beyond individual research.

Having strong linguistic ability is crucial for becoming a productive member of society. However, there remain many unanswered questions regarding how young children, who start out with no language whatsoever, learn this complex and crucial ability. The answer to these questions not only has educational ramifications but may also provide important insights into the root causes of such matters as the increased prevalence of cognitive-linguistic disorders and socioeconomic-status-based differences in learning outcomes. The issues examined in this dissertation project relate to how young children learn the meanings of verbs: Verbs constitute the core of a language's sentences, so understanding how verbs are learned is key to understanding how children learn language more generally. Some verbs are harder for children to learn than others. For instance, action verbs like "run" and "hit" are learned earlier than mental verbs like "believe" and "want". One reason "believe" and "want" might be learned later is that, whereas we can see and hear running and hitting events, we can't see or hear thinking and wanting. Children nevertheless learn these verbs, so a route other than the senses must exist. This research investigates what that route is using methods from linguistic theory, cognitive science, and computer science to examine one promising proposal: that children use the sentence contexts a verb occurs in to infer its meaning.

The research will examine theories of how children leverage the fact that similarity in sentence context seems to correspond to similarity in verb meaning. To answer this question, this research will exploit experimental methods for measuring the effect of contextual information on verb learning. The investigators will measure these effects on performance in artificial grammar learning experiments using Mechanical Turk for data collection. The researchers will incorporate the findings from these experiments into a computational model of the cognitive processes that allow children to learn words. This second step is useful both scientifically and practically. On the one hand, it will result in a deeper understanding of the mental processes that underlie language learning. On the other, it will provide a model of cognitive development that will help predict the effect that differences in the language spoken to children--for instance, those conditioned by socioeconomic status--have on language learning outcomes.

Humans have a special capacity to think and talk about possibilities beyond the here and now, enabling them to talk about impossible or hypothetical situations, such as what the world might be like if dinosaurs had survived, or whether next summer may be warmer than this one. How do children acquiring their first language figure what we are then discussing, when mere possibilities, unlike apples or naps, cannot be directly observed? And how do they come to use words, such as the modals "may" and "must", that are dedicated to saying what is possible or likely? This project pursues these developmental puzzles by probing how the use of modal words by children either matches or differs from that of their caregivers. The results will provide insights into two broader issues. What are the natural and unnatural ways of expressing possibility in human languages? And do the errors that children make sometimes lead to changes in modal language over time?

The project will be the most comprehensive linguistic study of modal development to date and will include both a series of behavioral experiments, and a corpus study of naturalistic speech between children and their caregivers. The experiments build on generalizations from studies of how modals change their meanings over time in the history of a language, and how they vary across languages. By exploiting this integration of theories of linguistic meaning and child development with theories of language change and variation, the project will bridge communities of researchers that are too seldom in contact. Outreach events supported by this project will enable high school students to participate in linguistic research on the language of possibility. Languages and dialects vary in how they talk about possibility, but also exhibit a common foundation. By understanding both how languages may vary and what is common among them, students who participate in the planned outreach activities will gain insight into the capacity that we share as humans for language and for the processes and representations that underlie abstract thought.

Language is used to communicate ideas and transfer information because it can reflect what our individual beliefs are and what our shared beliefs are. As one example, the way that words like "know" and "think" are used within a conversation reflects how sure the conversational participants are about what they believe, whether they agree about what they are discussing, and what they take to be facts or opinions. This project examines how children come to understand how belief words like "know" and "think" contribute to the exchange of information within a conversation. Do children from different backgrounds have similar experiences with these words? And to the degree that there are differences, how does that variation contribute to differences in acquiring an adult-like understanding of these words? To answer these questions, this project first conducts corpus analyses to investigate how parents use belief words in talking to their preschool-aged children. Then, these corpus results are combined with behavioral methods to reveal how linguistic experience relates to children's mastery of these words.

Finding out how children come to learn words like "know" and "think" is important in understanding contributing factors to later academic and professional success. Specifically, these words require an understanding of the ways that information is exchanged and communicated through conversations. As a result, understanding these words leads to mastery in interpreting what their conversational partners believe and why they believe it. This, in turn, allows children to better understand academic and professional communication and may lead to greater achievement in school, and ultimately, in their careers.