Understanding the unique relationship between language and human cognition

The diversity of the world's languages led many thinkers to speculate that linguistic diversity could also lead to cognitive diversity across speakers of different languages. This theory of linguistic relativity, most notably articulated in the Sapir-Whorf hypothesis, has generated rich debate about the relationship between language and thought. My research program sharpens this debate by asking whether language in any form supports uniquely human abilities to reason about the world. Moreover, I consider whether the relationship between language and cognition can be mediated by the modality of one's language: signed or spoken.

With support from the James S. McDonnell Foundation I will aim to pinpoint the exact nature of the relationship between language and cognition by combining laboratory research and fieldwork to investigate (a) aspects of human cognition that depend on having a language- any language, (b) effects of language modality, spoken or signed, on cognition, and (c) effects of cognition on the acquisition and emergence of language in the visual-spatial modality. Because experimental deprivation of language to children is unethical, I work with populations where we observe naturally occurring manipulations of language exposure: deaf children with delayed first-language exposure, learners of an emerging sign language in Nicaragua, and children and adults who acquired a sign language from birth. Each allows us to ethically isolate differential effects of language on cognition, and of cognition on language.

Within each of the three directions, I examine the same three areas: theory-of-mind, spatial cognition, and analogical reasoning. Theory-of-mind broadly refers to the understanding of internal states - intentions, desires, emotions, and beliefs-and that others' internal states can be different from one's own. In the domain of spatial cognition, my work investigates the ability to integrate multiple cues for navigation, engage in visual perspective-taking, and categorize the way in which objects are spatially located. With respect to analogical reasoning, I focus on the ability to detect and generate analogical mappings between a meaning (e.g., a location) and either a linguistic (e.g., a word) or non-linguistic (e.g., a map) representation.

By identifying the domains of human cognition that depend on language and vice versa, we gain deep insight into how language and cognition leveraged elements from each other over the course of evolution to engender modern human cognition. But just as importantly, we can identify points of intervention to foster success for language-delayed children, and we can develop expectations for the trajectory of language acquisition appropriate for the learners' language modality.