The second imaging technique is based on electroencephalogram (EEG) recordings of brain activity, measured at various scalp locations. Language scientists have used this technique to determine brainwave responses to language stimuli; these responses are averaged across language stimuli (e.g., a set of sentences of one type versus a set of sentences of another type) and also averaged over a number of participants. Electrical activity may be tracked over the course of a sentence, word by word, as the sentence unfolds.
The resulting electrical fluctuations are referred to as event-related potentials (ERPs): brainwave responses that are tied to stimulus events. ERP recordings are typically described in terms of electrode site on the scalp, polarity (negative versus positive fluctuations in the electrical charge), and timing with respect to a stimulus. Overall, ERP has been the technique of choice when the focus of the research question has been on issues of timing and functional MRI has been used to examine localization of function.
Within the ERP literature on language comprehension in monolinguals, a number of brainwave patterns or components have been identified. Next, we discuss three of these, in order of the timing of their appearance with respect to a stimulus, and provide an interpretation of each (though different interpretations have been offered in the literature and the descriptions here are certainly not uncontroversial).One component is a left-anterior negativity (LAN): a negative wave at anterior electrode sites in the left hemisphere.
This suggests that comprehension of a second (nondominant) language may be less efficient, or less automatic, than the processing of a first/dominant language. One would expect this of novice learners, but this appears to be true even of highly proficient users of a second language. Referring to the syntactic aspects, a number of investigators have found that ungrammaticality produces no very early effect (the N125), even in people who started learning a second language before the age of 3.
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