Functional magnetic resonance imaging (fMRI) studies have provided new data concerning the general brain regions associated with language processes, but a detailed analysis of these regions has not been accomplished. Although evidence links the temporal lobe to diverse linguistic functions including phoneme perception, visual word recognition, and semantic processing, there is little consensus regarding the location of component processes that underlie these functions. The goal of the proposed research program is to clarify the large-scale neural organization of temporal lobe auditory, visual, and polymodal pathways involved in word processing, using fMRI. The first specific aim is to distinguish regions associated with three levels of auditory information processing engaged during speech perception, including nonconfigural, feature, and phoneme processing, by demonstrating dissociations in sensitivity to intensity, auditory feature information, and phoneme intelligibility. The second specific aim is to distinguish regions associated with three levels of information processing relevant to visual word recognition, including grapheme perceptual, orthographic, and phonological processing, by demonstrating specific sensitivity to feature degradation, orthographic familiarity, and phonological processing demands during grapheme perception and lexical decision tasks. The third specific aim is to distinguish regions associated with word-level and concept-level information processing from those associated with sublexical phoneme and grapheme recognition, using manipulation of sublexical phonological, whole-word, and semantic processing load during lexical decision, phonological, and categorization tasks. The investigators hypothesize an interactive network of systems underlying word processing that includes a ventrally-directed auditory form recognition system located in dorsolateral temporal cortex, an anteriorly-directed visual-orthographic system in ventrolateral temporal cortex, and polymodal phonological and semantic systems located in lateral and ventromedial temporal convergence areas. Language dysfunction is a regular feature of brain illnesses affecting the dominant temporal lobe, including dementia, stroke, epilepsy, and schizophrenia. A detailed account of the organization of linguistic processes in this region would greatly aid in understanding and managing the breakdowns in language function that occur in these disorders.
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