Implicit and Explicit Measures of Sensitivity to Violations in Second Language Grammar: An Event-Related Potential Investigation
journal contributionposted on 2005-06-01, 00:00 authored by Natasha Tokowicz, Brian MacwhinneyBrian Macwhinney
We used event-related brain potentials (ERPs) to investigate the contributions of explicit and implicit processes during second language (L2) sentence comprehension. We tested 20 native English speakers enrolled in the first four semesters of Spanish classes, using an L2 grammaticality judgment task (GJT), while recording both accuracy and ERP data. We reasoned that any difference in the ERP between grammatical and ungrammatical sentences would reflect on-line, implicit processing, and that overt grammaticality judgments would reflect primarily explicit processing. We reasoned that because end-ofsentence grammaticality judgments are open to conscious inspection, they can be influenced by strategic processes that reflect on formal rules. On the other hand, because ERPs are a direct reflection of on-line processing, they reflect automatic, non-reflective, implicit responses to stimuli (Rugg et al, 1998; Schnyer et al., 1999; Tachibana et al., 1999). We used a version of the GJT that has been adapted for the ERP environment. The sentences were presented one word at a time; each word was presented for 300 ms with a blank between words of 350 ms. Grammaticality judgments were given after a brief delay following the last word of each sentence. Half of the sentences were grammatically acceptable. The critical sentences varied the form of three different syntactic constructions. First, we included sentences that were either acceptable or not in their tense-marking; this construction is formed similarly in L1 and L2. We also included sentences that were either acceptable or not in their determiner number agreement; this construction is formed differently in L1 and L2. Finally, we included sentences that were acceptable or not in their determiner gender agreement; this construction is unique to L2. Our analysis of the ERP data included both correct and incorrect trials, because past studies (e.g., Osterhout et al., 2000) have shown that the ERPs produced by beginning L2 learners show sensitivity to grammaticality, even when formal grammaticality judgments are near chance in terms of accuracy. We examined ERP responses during a time period between 500 and 900 ms following the onset of the critical (violation or matched control) word in the sentence because extensive past research has shown that grammatical violations elicit a positive-going deflection in the ERP waveform during this period (e.g., the “P600”; Osterhout & Holcomb, 1992). We found that learners were sensitive (i.e., showed brain responses that differed to grammatical and ungrammatical sentences) to violations in L2 for constructions that are formed similarly in L1 and L2, but were not sensitive to violations for constructions that differ in L1 and L2. Critically, a robust grammaticality effect was found in the ERP data for the construction that was unique to L2, suggesting that the learners were implicitly sensitive to these violations. Judgment accuracy was near chance for all constructions. These findings suggest that learners are able to implicitly process some aspects of L2 syntax even in early stages of learning, but that this knowledge depends on the similarity between L1 and L2. Furthermore, there is a divergence between explicit and implicit measures of L2 learning, which may be due to the behavioral task demands. We conclude that comparing ERP and behavioral data may provide a sensitive method for measuring implicit processing. In future research, we will attempt to improve the accuracy of grammaticality judgments using feedback, and then examine the consequences of these improvements for ERPs.