Cognitive science applies diverse tools and perspectives to study human language. Recently, an exciting body of work has examined linguistic phenomena through the lens of efficiency in usage: what otherwise puzzling features of language find explanation in formal accounts of how language might be optimized for communication and learning? Here, we review studies that deploy formal tools from probability and information theory to understand how and why language works the way that it does, focusing on phenomena ranging from the lexicon through syntax. These studies show how apervasive pressure for efficiency guides the forms of natural language and indicate that a rich future for language research lies in connecting linguistics to cognitive psychology and mathematical theories of communication and inference.

Previous studies suggest that mentally representing exact numbers larger than four depends on a verbal count routine (e.g. “one, two, three...”). However, these findings are controversial, as they rely on comparisons across radically different languages and cultures. We tested the role of language in number concepts within a single population – the Tsimane’ of Bolivia – where knowledge of number words varies across individual adults. We used a novel data analysis model to quantify the point at which participants switched from exact to approximate number representations during a simple numerical matching task. The results show that these behavioral switchpoints were bounded by participants’ verbal count ranges; their representations of exact cardinalities were limited to the number words they could recite. Beyond that range, they resorted to numerical approximation. These findings resolve competing accounts of previous findings and provide unambiguous evidence that large exact number concepts are enabled by language.

Speakers and listeners are thought to routinely make sophisticated inferences, in real time, about their conversation partner’s knowledge state and communicative intentions. However, these inferences have only been studied in industrialized cultures. Communicative expectations may be language-dependent, as are many phonological, syntactic, and semantic aspects of language. We study pragmatic inference in communication in the Tsimane’, an indigenous people of the Bolivian Amazon, who have little contact with industrialization or formal education. Using a referential communication task and eye-tracking, we probe how Tsimane' speakers use and understand referential expressions (e.g., ``Hand me the cup.'') across contexts. We manipulated aspects of the visual display to elicit contrastive inferences, including whether the referent was unique or part of a set as well as whether members of the same set differed in size or color. Strikingly, in all cases, patterns of behavior and eye-gaze of Tsimane' and English speakers were qualitatively identical, suggesting that real-time inference may be a core feature of human communication that is shared across cultures rather than a product of life in an industrialized society.