The neural and cognitive mechanisms of infants' word representations: The role of variability

Canadians live in an increasingly diverse and multi-accented context, which undoubtedly impacts infants' language acquisition. The proposed work will determine how children's word processing is influenced by this diversity, and will begin to characterize and understand the nature of infants' emerging word representations. In these experiments, I will focus on 11-to-14-month-olds and use eye-tracking and functional Near-Infrared Spectroscopy (fNIRS), which detects haemoglobin changes in the brain. In the three aims of this proposal, I will address how variability in speakers' linguistic properties (like accent) and social properties (like speaker race) supports language acquisition, and capture the nuances of early word representations. Aim 1: To understand infants' vocabulary acquisition, it is critical to delineate how word processing is supported by their changing brains. In Aim 1, I will compare infants processing of familiar pronunciations of known words and novel words using eye-tracking and fNIRS. Through this aim, I will gain insight into the underlying structure of infants' basic word representations, which will serve as a baseline for the remaining aims. Aim 2: Typically, young monolingual language learners struggle to recognize words when they are produced with an unfamiliar accent (e.g., Van Heugten & Johnson, 2017). They particularly struggle with accents that deviate further from their native accent (e.g., White & Morgan, 2008), and contain vowel shifts that induce phonological change (i.e., sound like a different vowel entirely) (e.g., Newman et al., 2018). In Aim 2, I will assess how infants process variant pronunciations of known words by manipulating the magnitude of variation and their exposure to the specific variants. From these experiments, I will be able to determine how flexible word representations are in infancy, and will identify the mechanisms that support accent accommodation. Aim 3: My previous work has shown that race has a profound influence on infants' word processing (e.g., Weatherhead & White, 2018; Weatherhead et al., Invited Resubmit). In Aim 3, I will determine how non-linguistic information impacts the recognition of familiar and variant pronunciations of known words by manipulating speaker using eye-tracking and fNIRS. In these final experiments, infants will hear the same auditory stimuli as in in the previous aims, but with an accompanying face. The results of these experiments are an essential missing link in the literature, as they will speak directly to whether word representations in infancy incorporate non-linguistic contextual information. This work takes a unique approach to studying language acquisition by looking at how diverse speakers play an integral role in the development of word representations. In a country as multicultural as Canada, work such as this is necessary for ecological models of human development.