Neuro-physiological processing of subject-verb agreement in L1 & L2 speakers of English

The question of how people understand sentences during sentence comprehension has intrigued researchers over the past three decades. The aim of sentence processing research is, on one hand, to gain insight on the processes and factors that facilitate successful sentence comprehension, and on the other hand, enhance our understanding on how these factors may influence language acquisition. One of the linguistic phenomena that has enabled researchers to investigate these processes is subject verb (S-V) agreement. This thesis contributes to sentence processing research by investigating how the relative perceptual salience of S-V agreement violations (due to type of agreement violation and utterance position) might impact agreement processing during on-line sentence comprehension, using the ERP technique. Previous ERP studies have often reported two ERP components—LAN and P600—in response to subject-verb (S-V) agreement violations (e.g., the boys *runs). However, the latency, amplitude and scalp distribution of these components have been shown to vary depending on various factors which include experimental-related issues, language proficiency or maturational development. One factor that has been recently shown to play a role in the comprehension of S-V agreement, but has not been given attention in sentence processing research, is perceptual salience. Understanding how the relative perceptual salience of the S-V agreement violations impacts on the listeners’ sensitivity to the violation is important for two reasons: i) it may enhance our understanding on how acoustic information modulate the processing and acquisition of grammatical morphemes (very few studies have used the auditory modality to investigate the processing of S-V agreement violations); and ii) it may contribute to on-going debates on the functional interpretation of the LAN/P600 ERP components. This thesis therefore reports findings from three different populations, i.e. adult English-speakers (L1), adult Mandarin-English learners (MLEs) and 8-11-year-old children, which constitute the three studies reported in the respective Chapter 2, 3, and 4 in this thesis. Participants were presented with four conditions varying in degree of perceptual salience depending on utterance position and type of agreement violation: utterance-medial errors of omission and errors of commission, and utterance-final errors of omission and errors of commission. In L1 adults, we observed more robust P600 effects for errors of commission in utterance-final position and a bilateral anterior negativity (AN) effect for errors of omission in utterance-medial position. This indicated that perceptual salience of the S-V agreement violations impacted on how L1 adults processed the agreement violations. In Mandarin learners of English (MLEs), we observed a late anterior P600 for errors of omission in utterance-final position and a late posterior negativity for errors of commission in utterance final position. Although MLEs showed sensitivity in the more perceptually salient utterance final position, the ERP components observed differed from those observed in L1 adults.Finally, in the 8-11-year-olds, we observed a broad N400 effect with longer latency for errors of omission in utterance-final position and a centro-posterior N400 with shorter latency in utterance-medial position. Although the children showed sensitivity in the more perceptually salient utterance-final position, the ERP components elicited differed from those observed inL1 and L2 adults. These findings highlight the importance of perceptual salience in S-V agreement processing and the potential theoretical implications it has for the processing and acquisition of grammatical morphemes such as the 3rd person singular –s. Furthermore, these findings highlight the implications of experimental designs used in ERP studies (e.g., stimuli manipulations and/or modalities of presentation) for the functional interpretation of the ERP effects observed thereof.