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Adults struggle to learn non-native speech categories in many experimental settings (Goto, 1971), but learn efficiently in a video game paradigm where non-native speech sounds have functional significance (Lim and Holt, 2011). Behavioral and neural evidence from this and other paradigms point toward the involvement of reinforcement learning mechanisms in speech category learning. We formalize this hypothesis computationally and present two simulations. The first simulates the findings of Lim et al. (2019), providing proof in principle that a reinforcement learning algorithm can successfully capture human results in a video game where people are learning novel categories of noise tokens. Our second simulation extends this to speech sounds and demonstrates that our algorithm mimics second language learners’ improvement on discrimination of a non-native speech contrast. Together these two simulations show that reinforcement learning provides an accurate model of human learning in this paradigm and provide evidence supporting the hypothesis that this mechanism could play a key role in effective speech category learning in adults. Being able to identify the algorithms employed in this paradigm could provide many avenues for pedagogical changes in second language learning and let teachers harness the processes that allow for efficient learning and improvement of non-native perceptual ability. 

Human listeners are better at telling apart speakers of their native language than speakers of other languages, a phenomenon known as the language familiarity effect. The recent observation of such an effect in infants as young as 4.5 months of age (Fecher & Johnson, in press) has led to new difficulties for theories of the effect. On the one hand, retaining classical accounts—which rely on sophisticated knowledge of the native language (Goggin, Thompson, Strube, & Simental, 1991)–requires an explanation of how infants could acquire this knowledge so early. On the other hand, letting go of these accounts requires an explanation of how the effect could arise in the absence of such knowledge. In this paper, we build on algorithms from unsupervised machine learning and zero-resource speech technology to propose, for the first time, a feasible acquisition mechanism for the language familiarity effect in infants. Our results show how, without relying on sophisticated linguistic knowledge, infants could develop a language familiarity effect through statistical modeling at multiple time-scales of the acoustics of the speech signal to which they are exposed.