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Proficiency-related shifts from bilateral to native-like left-lateralized P600 responses during non-adjacent dependency learning
Poster Session C, Thursday, October 1, 10:45 am - 12:45 pm, Wangari Maathai
Yi-Chun Ko1, Chih Yeh2,3, Hsin-Jen Hsu4, Chia-Lin Lee1; 1National Taiwan University, 2Max Planck Institute for Psycholinguistics, 3Max Planck School of Cognition, 4National Tsing Hua University
Non-adjacent dependencies (NADs) are a core feature of language, providing crucial cues for extracting syntactic structure from continuous input. Previous behavioral and neural studies have shown that adults can rapidly acquire sensitivity to such dependencies. However, more nuance about how this learning unfolds in the brain awaits further investigation. Prior Event-Related Potential (ERP) research suggests that syntactic computation involves differential contributions from the two hemispheres. In response to phrase violations relative to grammatical constructions, native speakers typically show a left-hemisphere (LH)–lateralized P600 and a right-hemisphere (RH) N400. In contrast, intermediate second-language learners and older adults, who generally exhibit lower behavioral accuracy, tend to show RH or bilateral P600 effects. Although these patterns have been observed across populations differing in age, language background, and processing experience, the extent to which they specifically reflect proficiency remains uncertain. The present study therefore used two ERP experiments to investigate hemispheric dynamics during non-adjacent dependency learning and to test whether these patterns shift with increasing proficiency. Both experiments contain training and testing phases. Participants listened to four pairs of three-element pseudoword strings with an A-X-B structure, in which the first and third items formed NAD pairs across a variable intervening item (drawn from a set of 24 items). Stimuli were presented monaurally to bias initial processing toward the contralateral hemisphere. The four dependency pairs were divided into two sets, with each ear receiving two pairs. During the testing phase, half of the strings were grammatical items heard during training, whereas the remaining half were ungrammatical strings created by swapping final items between dependency pairs within the same ear of presentation. In Experiment 1, 40 young adults completed a 192-trial training phase followed by a 192-trial testing phase. Participants achieved high behavioral accuracy (right ear: 74%; left ear: 75%). ERPs time-locked to the third item revealed P600 effects for ungrammatical relative to grammatical pairs regardless of ear presentation, indicating involvement of both hemispheres in processing dependency violations. Experiment 2 further investigated whether hemispheric patterns would gradually shift toward a more native-like profile as proficiency increased. Thirty-five young adults completed the same number of trials distributed across four shorter learning–test cycles (i.e., a 48-trial learning phase followed by a 48-trial testing phase per cycle). Such a design allowed for the examination of learners’ emerging grammatical representations across learning cycles. Analyses focused on data from the second half of the experiment in participants whose accuracy exceeded 90% after the third cycle (N = 24; right ear: 99%; left ear: 98%). ERP data from these learners revealed an LH-biased P600 effect and an RH-biased N400 effect, consistent with the profile previously reported for native speakers processing syntactic violations. Overall, our findings replicate prior studies showing that young adults can acquire NADs after relatively brief exposure. The results also highlight a qualitative shift in RH responses during syntactic dependency learning. Most importantly, the present study demonstrates that increasingly native-like hemispheric response patterns may emerge as learners achieve higher proficiency with the dependency structure.
Topic Areas: Language Development/Acquisition, Syntax and Combinatorial Semantics