Relations between the neural bases of dynamic auditory processing and phonological processing: Evidence from fMRI

Functional magnetic resonance imaging (fMRI) was used to examine how the br ain responds ri, temporal compression of speech and to determine whether th e same regions are also involved in phonological processes associated with reading. Recorded speech was temporally compressed to varying degrees anti presented in a sentence verification task. Regions involved in phonological processing were identified in a separate scan using a rhyming judgment tas k with pseudo-words compared to a lettercase judgment task. The left inferi or frontal and left superior temporal regions (Broca's and Wernicke's areas ), along with the right inferior frontal cortex. demonstrated a convex resp onse to speech compression; their activity increased as compression increas ed, but then decreased when speech became incomprehensible. Other regions e xhibited linear increases in activity as compression increased, including t he middle frontal gyri bilaterally. The auditory cortices exhibited compres sion-related decreases bilaterally, primarily reflecting a decrease in acti vity when speech became incomprehensible. Rhyme judgments engaged two left inferior frontal gyrus regions (pars triangularis and pars opercularis), of which only the pars triangularis region exhibited significant compression- related activity. These results directly demonstrate that a subset of the l eft inferior frontal regions involved in phonological processing is also se nsitive to transient acoustic features within the range of comprehensible s peech.