Relations between the Neural Bases of Dynamic Auditory Processing and Phonological Processing: Evidence from fMRI

TLDR

The study used fMRI to examine how the brain responds to temporal compression of speech and to determine whether the same regions are also involved in phonological processes associated with reading. The authors recorded temporally compressed speech at multiple levels and presented it in a sentence‑verification task, while a separate scan used a rhyming‑judgment task with pseudowords versus a letter‑case control to localize phonological processing regions. The left inferior frontal and left superior temporal areas, along with right inferior frontal cortex, showed a convex response to speech compression—activity rose with moderate compression and fell when speech became incomprehensible—while middle frontal gyri increased linearly and auditory cortices decreased; rhyme judgments activated two left inferior frontal regions, with only the pars triangularis exhibiting compression‑related activity, indicating that a subset of phonological processing regions also responds to transient acoustic features.

Abstract

Abstract Functional magnetic resonance imaging (fMRI) was used to examine how the brain responds to temporal compression of speech and to determine whether the same regions are also involved in phonological processes associated with reading. Recorded speech was temporally compressed to varying degrees and presented in a sentence verification task. Regions involved in phonological processing were identified in a separate scan using a rhyming judgment task with pseudowords compared to a lettercase judgment task. The left inferior frontal and left superior temporal regions (Broca's and Wernicke's areas), along with the right inferior frontal cortex, demonstrated a convex response to speech compression; their activity increased as compression increased, but then decreased when speech became incomprehensible. Other regions exhibited linear increases in activity as compression increased, including the middle frontal gyri bilaterally. The auditory cortices exhibited compression-related decreases bilaterally, primarily reflecting a decrease in activity 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 left inferior frontal regions involved in phonological processing is also sensitive to transient acoustic features within the range of comprehensible speech.