Early linguistic experiences are intimately tied to later language learning outcomes (e.g., Chilosi et al., 2013; Kaushanskaya & Marian, 2009b). The underlying neural and cognitive processes mediating this relationship remain unclear. Pierce, Genesee, Delcenserie, and Morgan (2017) propose that the phonological working memory (PWM) system is the critical component responsible for linking early linguistic experiences to later language development. Their argument arises from research demonstrating that exposure to linguistic input early in life shapes the kinds of phonological representations that are formed about the sounds within one's native language (Kuhl, 2004; Majerus et al., 2005; Mody, Schwartz, Gravel, & Ruben, 1999; Nittrouer & Burton, 2005). These phonological representations, which the authors believe to be created and stored using the PWM system (Gathercole & Baddeley, 1989), are highly predictive of later language outcomes (Bernhardt, Kemp, & Werker, 2007; Kuhl, 2010; Molfese & Molfese, 1985; Tsao, Liu, & Kuhl, 2004). Explaining language development via memory processes has many benefits. For instance, drawing on a large extant literature on memory-related processes allows researchers to make novel predictions about language learning, especially in regard to its connections to other kinds of learning (e.g., Gathercole, 2006). Identifying PWM as a key driver to language development is a useful insight likely to generate much further research, but it may not go far enough in tying language acquisition to more domain-general aspects of the human cognitive architecture. We believe that a complete account of language will require consideration of additional aspects of the human cognitive architecture working alongside the PWM system.

Language learning, while seemingly effortless for young learners, is a complex process involving many interacting pieces, both within the child and in their language-learning environments, which can result in unique language learning trajectories and outcomes. How does the brain adjust to or accommodate the myriad variations that occur during this developmental process. How does it adapt and change over time? In our review, we proposed that the timing, quantity, and quality of children's early language experiences, particularly during an early sensitive period for the acquisition of phonology, shape the establishment of neural phonological representations that are used to establish and support phonological working memory (PWM). The efficiency of the PWM system in turn, we argued, influences the acquisition and processing of more complex aspects of language. In brief, we proposed that experience modulates later language outcomes through its early effects on PWM. We supported this claim by reviewing research from several unique groups of language learners who experience delayed exposure to language (children with cochlear implants [CI] or internationally adopted [IA] children, and children with either impoverished [signing deaf children with hearing parents)] or enriched [bilingual] early language experiences). By comparing PWM and language outcomes in these groups, we sought to highlight general patterns in language development that emerge based on variation in early language exposure. Moving forward, we also proposed that the language acquisition patterns in these groups, and others, can be used to understand how variability in early language input might affect the neural systems supporting language development and how this might affect language learning itself.