"Where go, huh?" Young children's use of huh challenges assumptions about language development

The capacity for language sets humans apart from other animals and the exploration of human language is intimately tied to the exploration of human cognition. Thus, the development of language in children serves as a window into cognitive development. Much of this research on language development focusses on aspects of language tied to the construction of sentences and the representation of information about objects and events in the world. This includes nouns and verbs in their inflected forms along with the grammatical elements necessary to complete a sentence. According to this research tradition, linguistic development starts at the two-word stage (at around 2 years), when children first combine words with each other.           What this line of research overlooks is the fact there are aspects of language that are tied to managing verbal interaction, including turn-taking and the construction of common ground. There are units of language dedicated to these interactional aspects of language (e.g., little words like huh, uhm, oh, mhm) and they are systematically integrated into the way sentences are used in interaction. Crucially, children start using interactional words as soon as they start being verbal, and significantly, they start combining them with their first words well before they enter the officially recognized two-word stage. Consequently, classic studies of language development miss the real onset of linguistic combinatorial abilities. In addition, ignoring the development of interactional words means that we are missing out on an important linguistic window into cognitive development, namely in the areas of social interaction, the construction of common ground, as well as theory of mind.            By exploring the use of utterance final huh as well as the use of response tokens in child speech, we have identified 3 stages. Stage 1 (10-28 months) is characterized by the ability to participate in turn-taking; Stage 2 (28-42 months) is characterized by the recognition that there is a shared set of beliefs (a common ground) between interlocutors; and Stage 3 (starting around 42 months) is characterized by the recognition that beliefs may differ.