Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Psychology

Supervisor

Joanisse, Marc F.

Abstract

Adults struggle with learning language components involving categorical relations such as grammar while achieving higher proficiency in vocabulary. The cognitive and neural mechanisms modulating this learning difference remain unclear. The present thesis investigated behavioural and neural differences between vocabulary and grammar processing in adults using functional Near-Infrared Spectroscopy (fNIRS). Participants took part in an artificial language learning paradigm consisting of novel singular and plural words paired with images of common objects. Findings revealed higher accuracy scores and faster response times on semantic vocabulary judgement trials compared to grammar judgement trials. Singular vocabulary judgement was associated with neural activity in part of the pars triangularis of the right inferior frontal gyrus associated with semantic recall. On the other hand, bilateral portions of the dorsolateral prefrontal cortex were more active during grammar judgement tasks. The results are discussed with reference to the roles of memory mechanisms and interference effects in language learning.

Summary for Lay Audience

Adults struggle with some aspects of second language learning more than others. Particularly, their proficiency outcomes in grammar are lower than in vocabulary. It remains unclear why differences between vocabulary and grammar learning exist in adults, and what brain areas are involved in contributing to this difference. Using an artificial language, this thesis investigated both performance and brain activity differences between processing novel vocabulary words and grammatical patterns. We used functional Near-Infrared Spectroscopy (fNIRS) which is a neuroimaging method that measures brain activity through light diffraction measured through the skull. Participants were taught an artificial language consisting of novel singular and plural words paired with images of common objects. Grammatical plural patterns were learned implicitly through repeated exposure to the language. On the other hand, vocabulary was learned explicitly through the pairing of a word and its meaning. As in natural second language learning, participants learned vocabulary more accurately than grammar. During a vocabulary judgement task, brain activity was greater in areas known to be involved in semantic recall. On the other hand, during grammar judgement tasks, brain activity was greater in areas known to be involved in complex executive functioning that develop into young adulthood. The results are discussed with reference to the roles of memory processes and interference effects in language learning.

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