Examining the Neural Correlates of Vocabulary and Grammar Learning Using fNIRS

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