In this article we review several studies investigating the neural correlates of secondlanguage (L2) grammatical learning in the context of novice adult learners progressing through their first year of L2 classroom instruction. The primary goal of these studies was to determine how and when learners incorporate L2 knowledge into their online language processing system. We show that at least some learners progress through discrete stages of grammatical learning during the first year of instruction. These stages are robust across languages, experimental tasks, and levels of language (lexical vs. sentential) and indicate that there is an intermediate stage of learning between no L2 grammatical knowledge and grammaticalization. We also show that although learners' brain responses are quite variable, this variability is highly systematic and can be used to identify meaningful subgroups of learners.

Using event-related potentials (ERPs), we investigated the impact of a range of individual difference measures related to L2 learning on proficient L1 Spanish – L2 English bilinguals’ brain responses during L2 morphosyntactic processing. Although grand mean ERP analyses revealed a biphasic N400–P600 response to English subject–verb agreement violations, subsequent analyses showed that participants’ brain responses varied along a continuum between N400- and P600-dominance. To investigate this pattern, we introduce two novel ERP measures that independently quantify relative brain response type and overall magnitude. Multivariate analyses revealed that larger overall brain responses were associated with higher L2 proficiency, while relative brain response type (N400 or P600) was predicted by a coalition of variables, most notably learners’ motivation and age of arrival in an L2 environment. Our findings show that aspects of a learner's background can differentially impact a learner's overall sensitivity to L2 morphosyntax and qualitative use of linguistic cues during processing.

Presumably, second-language (L2) learning is mediated by changes in the brain. Little is known about what changes in the brain, how the brain changes, or when these changes occur during learning. Here, we illustrate by way of example how modern brain-based methods can be used to discern some of the changes that occur during L2 learning. Preliminary results from three studies indicate that classroom-based L2 instruction can result in changes in the brain's electrical activity, in the location of this activity within the brain, and in the structure of the learners' brains. These changes can occur during the earliest stages of L2 acquisition.

Even though auditory training exercises for humans have been shown to improve certain perceptual skills of individuals with and without hearing loss, there is a lack of knowledge pertaining to which aspects of training are responsible for the perceptual gains, and which aspects of perception are changed. To better define how auditory training impacts brain and behavior, electroencephalography (EEG) and magnetoencephalography (MEG) have been used to determine the time course and coincidence of cortical modulations associated with different types of training. Here we focus on P1-N1-P2 auditory evoked responses (AEP), as there are consistent reports of gains in P2 amplitude following various types of auditory training experiences; including music and speech-sound training. The purpose of this experiment was to determine if the auditory evoked P2 response is a biomarker of learning. To do this, we taught native English speakers to identify a new pre-voiced temporal cue that is not used phonemically in the English language so that coinciding changes in evoked neural activity could be characterized. To differentiate possible effects of repeated stimulus exposure and a button-pushing task from learning itself, we examined modulations in brain activity in a group of participants who learned to identify the pre-voicing contrast and compared it to participants, matched in time, and stimulus exposure, that did not. The main finding was that the amplitude of the P2 auditory evoked response increased across repeated EEG sessions for all groups, regardless of any change in perceptual performance. What’s more, these effects are retained for months. Changes in P2 amplitude were attributed to changes in neural activity associated with the acquisition process and not the learned outcome itself. A further finding was the expression of a late negativity (LN) wave 600–900 ms post-stimulus onset, post-training exclusively for the group that learned to identify the pre-voiced contrast.