Electrophysiological investigations of lexical ambiguity resolution

In this dissertation, I took advantage of a very common phenomenon, lexical ambiguity, to address the question of how human brains resolve the one-to-many mapping problems in language comprehension (e.g. whether the word 'watch' should be interpreted as a timing device or an action). Specifically, in a series of studies, I evaluated the interplay between different neural resources under varying levels of semantic constraints. In general, I found that the engagement of neural activity to suppress contextually irrelevant meanings, indexed by a frontal negativity ERP effect, was dependent on the amount of semantic information that is available for ambiguity resolution. This process showed a collaborative relationship with more implicit semantic processes, indexed by the N400. In subsequent studies, I also evaluated whether there are age-related differences in neural processes involved in lexical ambiguity resolution. The findings showed that healthy older adults maintained implicit semantic processing. However, the tendency and/or ability to recruit processing resources important for suppressing alternative meaning features under more difficult meaning selection conditions is diminished with advancing age, which further impacts meaning processing for linguistic material subsequent to the not- yet- resolved lexical ambiguity. Such age-related changes do not seem inevitable, however, as a subset of older adults with higher verbal fluency scores maintained a young-like frontal negativity effect pattern. Collectively, this series of studies provides strong evidence for the multi-faceted nature of language processing, in which the recruitment of and interplay among neural resources may be differentially tuned by contextual information and processing capacity