The end-result of perceptual reorganization in infancy is currently viewed as a reconfigured perceptual space, “warped” around native-language phonetic categories, which then acts as a direct perceptual filter on any non-native sounds: naïve-listener discrimination of non-native-sounds is determined by their mapping onto native-language phonetic categories that are acoustically/articulatorily most similar. We report results that suggest another factor in non-native speech perception: some perceptual sensitivities cannot be attributed to listeners’ warped perceptual space alone, but rather to enhanced general sensitivity along phonetic dimensions that the listeners’ native language employs to distinguish between categories. Specifically, we show that the knowledge of a language with short and long vowel categories leads to enhanced discrimination of non-native consonant length contrasts. We argue that these results support a view of perceptual reorganization as the consequence of learners’ hierarchical inductive inferences about the structure of the language’s sound system: infants not only acquire the specific phonetic category inventory, but also draw higher-order generalizations over the set of those categories, such as the overall informativity of phonetic dimensions for sound categorization. Non-native sound perception is then also determined by sensitivities that emerge from these generalizations, rather than only by mappings of non-native sounds onto native-language phonetic categories.

We present a framework of second and additional language (L2/Ln) acquisition motivated by recent work on socio-indexical knowledge in first language (L1) processing. The distribution of linguistic categories covaries with socio-indexical variables (e.g., talker identity, gender, dialects). We summarize evidence that implicit probabilistic knowledge of this covariance is critical to L1 processing, and propose that L2/Ln learning uses the same type of socio-indexical information to probabilistically infer latent hierarchical structure over previously learned and new languages. This structure guides the acquisition of new languages based on their inferred place within that hierarchy, and is itself continuously revised based on new input from any language. This proposal unifies L1 processing and L2/Ln acquisition as probabilistic inference under uncertainty over socio-indexical structure. It also offers a new perspective on crosslinguistic influences during L2/Ln learning, accommodating gradient and continued transfer (both negative and positive) from previously learned to novel languages, and vice versa.

How are languages learned, and to what extent are learning mechanisms similar in infant native-language (L1) and adult second-language (L2) acquisition? In terms of vocabulary acquisition, we know from the infant literature that the ability to discriminate similar-sounding words at a particular age does not guarantee successful word-meaning mapping at that age (Stager & Werker, 1997). However, it is unclear whether this difficulty arises from developmental limitations of young infants (e.g., poorer working memory) or whether it is an intrinsic part of the initial word learning, L1 and L2 alike. Here we show that adults of particular L1 backgrounds—just like young infants—have difficulty learning similar-sounding L2 words that they can nevertheless discriminate perceptually. This suggests that the early stages of word learning, whether L1 or L2, intrinsically involve difficulty in mapping similar-sounding words onto referents. We argue that this is due to an interaction between two main factors: (1) memory limitations that pose particular challenges for highly similar-sounding words, and (2) uncertainty regarding the language's phonetic categories, as these are being learned concurrently with words. Overall, our results show that vocabulary acquisition in infancy and in adulthood share more similarities than previously thought, thus supporting the existence of common learning mechanisms that operate throughout the lifespan.

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The Challenge As more and more learners use digital apps to learn languages, it is important for the field of language learning to understand the effectiveness of these apps. This article presents the listening and reading proficiency of Duolingo learners when they reach the end of its beginning-level Spanish and French courses.