In defining the language acquisition problem, traditional models abstract away effects of variability, defining the learner as acquiring a single language variety, which is spoken homogeneously by their speech community. However, infants are exposed to as many unique varieties of speech as they are speakers. Adult sociolinguistic competence is also characterized by the capacity to employ and interpret non-phonological linguistic distinctions which are associated with different social groups, including ‘code-switching’ or ‘style-shifting’ between languages and speech registers.

This dissertation presents a model of infant lexical acquisition which assumes that learners monitor linguistic sources for variation in reliability. This model is adapted from Shafto, Eaves, Navarro, and Perfors (2012) which the authors used to describe the behavior of preschool children in selecting sources to learn labels from in K. Corriveau and Harris (2009) and M. Corriveau and Harris (2009). I show that this probabilistic model effectively simulates two experiments from the literature on preverbal infants’ perception of labeling, Rost and McMurray (2009) and Koenig and Echols (2003). Evidence suggests that the receptiveness of preverbal infants to novel lexical items is correlated with infant beliefs regarding the informant’s knowledgeability and social group membership. These simulations demonstrate that language learners may well be recruiting processes of epistemic trust to guide lexical acquisition much earlier than previously suggested.

We should therefore expect even very young listeners to respond differently to dialects not solely as a function of exposure, but also as a function of attitudes towards the speech determined by the quality of that exposure. Developmental differences between populations in attention to non-linguistic affiliative cues are therefore expected to emerge early and have significant effects on language outcomes. Measures of online language proficiency may be vulnerable to significant bias owing to the activation of sociolinguistic biases in the presentation of test items. Differences in the breadth or specificity of listener preferences for speakers in turn predict differences in task complexity for learners of standard and non-standard dialects. A new research program in early sociophonetic perception, uniting accounts of selective trust with language learning has the potential to deepen understanding of both typical and disordered language development.