Explicit and implicit second language training differentially affect the achievement of native-like brain activation patterns

Abstract

It is widely believed that adults cannot learn a foreign language in the same way that children learn a first language. However, recent evidence suggests that adult learners of a foreign language can come to rely on native-like language brain mechanisms. Here, we show that the type of language training crucially impacts this outcome. We used an artificial language paradigm to examine longitudinally whether explicit training (that approximates traditional grammar-focused classroom settings) and implicit training (that approximates immersion settings) differentially affect neural (electrophysiological) and behavioral (performance) measures of syntactic processing. Results showed that performance of explicitly and implicitly trained groups did not differ at either low or high proficiency. In contrast, electrophysiological (ERP) measures revealed striking differences between the groups' neural activity at both proficiency levels in response to syntactic violations. Implicit training yielded an N400 at low proficiency, whereas at high proficiency, it elicited a pattern typical of native speakers: an anterior negativity followed by a P600 accompanied by a late anterior negativity. Explicit training, by contrast, yielded no significant effects at low proficiency and only an anterior positivity followed by a P600 at high proficiency. Although the P600 is reminiscent of native-like processing, this response pattern as a whole is not. Thus, only implicit training led to an electrophysiological signature typical of native speakers. Overall, the results suggest that adult foreign language learners can come to rely on native-like language brain mechanisms, but that the conditions under which the language is learned may be crucial in attaining this goal.

Figure 1

Computer-based game board. Game tokens are represented by visual symbols, which correspond to nouns in Brocanto2. The tokens can further be distinguished by their background shape—square or round—each of which corresponds to a Brocanto2 adjective. Players can move, swap, capture, and release tokens, with each of these actions corresponding to Brocanto2 verbs, as well as move them either horizontally or vertically (corresponding to Brocanto2 adverbs).

Figure 2

The experimental design consisted of three sessions during which background questionnaires, pretraining (learning the rules of the computer-based game, and the names of the four game tokens), explicit and implicit artificial language training, practice, and assessments were administered. Arrows indicate whether the subsequent experimental procedure was the same (downward and inward pointing arrows) or different (outward pointing arrows) for the explicit and implicit training conditions.

Figure 3

Mean d′ scores and standard errors for the explicitly trained and implicitly trained participant groups at low proficiency and at high proficiency. Paired t tests on d′ scores motivated by a Group× Test Session interaction (see Results) indicated that the two groups did not differ in their ability to distinguish correct and violation sentences, at either low proficiency (t(28) = 5.61, p = .579) or high proficiency (t(28) = 1.24, p = .226). Both groups improved from the first to the second test session (explicit: t(28) = 4.80, p < .001; implicit: t(28) = 7.47, p < .001), although the improvement was larger for the implicit than the explicit group, as indicated by the Group × Test Session interaction. At high proficiency, the d′ scores of both groups were above 2.5, which corresponds roughly to a proportion correct of 0.90 (Macmillan & Creelman, 2005), indicating that both groups had reached a high level of proficiency.

Figure 4

Voltage maps and waveforms reflecting the difference between correct and violation sentence grand average ERPs. (A) Explicitly trained learners at low proficiency do not evidence any significant ERP effect. (B) Explicitly trained learners at high proficiency show an anterior positivity followed by a P600. (C) Implicitly trained learners at low proficiency show a broad, ongoing N400. (D) Implicitly trained learners at high proficiency show an AN followed by a P600 and a late AN. Voltage map coloration indicates amplitude differences between correct and violation waveforms.