Neurocognitive Correlates of Nouns and Verbs: Zero-Derivation and Lexico-Semantic ProcessesPublic Deposited
In the past few decades, psycholinguistic and neurolinguistic research has shown that nouns and verbs are processed differently in cognitively healthy individuals, and can be selectively impaired in aphasic individuals. However, this noun-verb dichotomy is poorly understood. This dissertation investigated cognitive and neural distinctions between nouns and verbs by studying categorically ambiguous words in English, providing insight into the domains of category ambiguity and derivational morphology. Using grammaticality judgment tasks and fMRI, three studies tested whether the two forms (noun/verb) of ambiguous words (e.g., brush) are listed under separate lexical entries or share a single entry with one form being zero-derived from the other. Studies 1 and 2 examined processing of noun-derived forms like brush and verb-derived forms like bite, presented for grammaticality judgment with either the or to, and response time and selection rates were measured. Results showed that for healthy speakers, derived forms (to brush, the bite) induced greater processing cost and, therefore, delayed recognition when compared to base forms (the brush, to bite) (Study 1). Additionally, base forms were selected more frequently compared to derived forms across categories in both healthy and aphasic participants without verb impairments, while decreased selection rates of verbal base forms occurred in aphasic participants with verb impairments (Study 2), indicating that impaired access to verb-base forms precluded retrieval of associated verb-derived nouns. These findings support the existence of a single base-form entry for ambiguous words in normal and impaired lexical processing. Study 3 used fMRI to examine the neurocognitive correlates of noun-derived verbs (to brush), non-derived verbs (to bear) and unambiguous verbs (to bake), compared to nouns (the bell). A distinct left frontal and bilateral temporal neural basis for verbs and nouns, respectively, was observed, suggesting that separable cognitive and neural systems are implicated in the processing of each word-class. A distinct bilateral temporal and left fronto-parietal neural activation pattern for noun-derived verbs vs. non-derived verbs was identified, suggesting a relation between morphological and semantic complexity, respectively, and neural processing. Overall, these data provide behavioral and neural support for a zero-derivation.