Altered frontal and dorsal hemodynamic engagement during mandarin aspiration processing in post-stroke aphasia: an fNIRS study

Auditory and speech-perception difficulties are common in post-stroke aphasia (PSA), but cortical responses during passive listening to Mandarin speech remain underexplored. Seventeen Mandarin-speaking individuals with PSA and 18 matched healthy controls listened to auditory oddball blocks containing /ba/ standards and /pa/ deviants during functional near-infrared spectroscopy (fNIRS). Although these syllables instantiate an aspiration contrast strongly cued by voice onset time (VOT), standard and deviant trials were combined within a single block-level condition. The resulting measures therefore indexed activation during speech-containing blocks relative to silent inter-block intervals rather than phonemic discrimination, categorization, or VOT-specific processing. Seven theory-driven channels covering bilateral auditory, sensorimotor, inferior frontal, and dorsolateral prefrontal regions were analyzed using three HbO indices: β coefficient, peak amplitude, and temporal centroid. The PSA group showed an overall reduction in task-related HbO activation, reflected by a significant Group effect for the β coefficient. Peak amplitude also showed significant Group and Group × Channel effects, although no individual channel remained significant after correction for multiple comparisons. Temporal centroid showed no significant group or interaction effects. These findings provide preliminary evidence for reduced block-evoked cortical recruitment during passive auditory exposure to Mandarin speech sounds in PSA. Because the analysis did not include a direct standard-deviant or active auditory control comparison, the findings do not establish a selective impairment of phonemic discrimination, categorization, or VOT processing. Because patients were assessed 6-7 months after stroke onset, the activation differences may reflect both persistent impairment and recovery-related reorganization during the early chronic stage.