Neural Correlates of Word and Syllable Frequency: An
Investigation of the Dual-Route Hypothesis

M Rogers, S McLaughlin, D Shibata

 

The current investigation used blood oxygenation level- dependent functional magnetic resonance imaging (BOLD fMRI) to investigate whether high and low frequency words and syllables are cognitively produced in the same manner as measured by the site and extent of activated regions.  The experiment examines the hypothesis that the neural activation associated with the production of frequently-occurring words and syllables differs significantly from activation associated with infrequently-occurring exemplars. The motivation is to investigate these potential differences stems from the dual-route theory of spoken language production, which posits that neural programs for the articulatory movements to produce frequently used syllables and words may be stored as pre-assembled units, or “movement gestalts,” while the programs for infrequently-occurring syllables and words are hypothesized to be assembled afresh from sub-lexical components each time they are produced (Rogers & Spencer, 2001; Varley & Whiteside, 2001). Production of low frequency words and nonsense strings was associated with significant cerebellar activation whereas the high frequency tokens were not.  These results will be discussed in terms of how these data address dual-routes of processing for spoken language production.  Methodological issues related to using fMRI during speech production will also be addressed.