1 School of Communication Sciences and Disorders, Faculty of Medicine and Health Sciences, McGill University, Montréal, Québec, Canada.
2 Centre for Research on Brain, Language and Music, Montréal, Québec, Canada.
3 Department of Psychology, Concordia University, Montréal, Québec, Canada.
4 Centre for Research in Human Development, Concordia University, Montréal, Québec, Canada.
5 Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada.

Language mixing is a common feature of many bilingually-raised children's input. Yet how it is related to their language development remains an open question. The current study investigated mixed-language input indexed by observed (30-second segment) counts and proportions in day-long recordings as well as parent-reported scores, in relation to infant vocal activeness (i.e., volubility) when infants were 10 and 18 months old. Results suggested infants who received a higher score or proportion of mixed input in one-on-one social contexts were less voluble. However, within contexts involving language mixing, infants who heard more words were also the ones who produced more vocalizations. These divergent associations between mixed input and infant vocal development point for a need to better understand the causal factors that drive these associations.