This study investigated the language expertise hypothesis on mouth-looking in toddlerhood and explored potential culture and sex effects. Polish and Norwegian 18- and-24-month-olds (N = 101; 44.55% females; data collected 2022-2024) viewed a speaker telling a story in familiar and unfamiliar languages. Toddlers showed more mouth-than-eyes looking across age groups, suggesting more mouth interest. They also showed greater mouth-looking in familiar languages, indicating language familiarity effects. Toddlers with larger vocabularies showed more mouth-looking in unfamiliar languages, possibly seeking helpful phonological-visual cues. These data show that mouth-looking continues supporting language development in toddlerhood in ways related to prior language experience. Exploratory analyses showed important differences in language acquisition and mouth-looking by language or culture and sex; potential mechanisms for such effects are discussed.
Lozano et al. (Wed,) studied this question.