Gallagher, D. C. | bioRxiv Science

bioRxiv2022

Causal evidence for the involvement of Broca's area in second language acquisition: A longitudinal HD-tDCS study

A wealth of correlational evidence suggests that Brocas area (the left inferior frontal gyrus) plays a role in second language acquisition. With the use of highly focal non-invasive brain stimulation, evidence for a targeted brain regions causal role in some cognitive behavior can be assessed. Over three sessions, each one week apart, we used online anodal high-definition transcranial direct current stimulation (HD-tDCS) over Brocas area during a novel foreign grammar training session. During training, participants who were naive to Spanish were tasked with acquiring present tense conjugation rules for the three Spanish verb endings. In Session 1, we observed significant improvement in performance in two linguistic (reception and production) tasks but not in a non-linguistic (working memory) task. Sessions 2 and 3 were subject to a ceiling effect, which obscured any potentially long-lasting effects of the stimulation. We interpret these results as support for the idea that Brocas area has languagelike specificity that is not limited to receptive or productive processes and as evidence that Brocas area plays a causal role in foreign grammar acquisition.

neuroscience↗

bioRxiv2022

The Neurophysiological Modality Effect in Native and Second Language Processing: An ERP Study

Experimental psychology has long discussed the modality effect, whereby the stimulus modality significantly affects retention of the information presented. In neurolinguistics, however, the effect of stimulus modality on language processing has gained little attention. We conducted a multi-modal event-related potential (ERP) experiment on both native and non-native Spanish speakers to investigate the possibility of a neurophysiological modality effect in language processing. Using morphosyntactically violated and orthographically/phonologically violated stimuli, we elicited a robust N400 and P600 in native speakers. We showed that the N400 has consistent features across modalities, while the P600 has modality-specific features. Specifically, the auditory evoked P600 was characterized by a more gradual slope and a later peak than the visual evoked P600. We discuss this in detail along with other modality effects observed post sensory perception. Among second language (L2) learner groups, those with higher proficiency exhibited more nativelike neurophysiological responses in both modalities when compared to those with lower proficiency. We additionally observed fewer modality-specific differences in low proficiency learners than in higher proficiency learners suggesting that modality-specific specialization in language processing comes with increased proficiency. We further discuss the question of modality-specific differences in the process of neurophysiological nativization, whereby L2 learners ERPs become increasingly on nativelike.

neuroscience↗