The impact of hearing loss on tone discrimination: An fMRI study

Hearing deprivation induces structural and functional reorganization in the brain, which compromises an individual's language processing capacity. As a tonal language, Mandarin Chinese requires fine-grained auditory processing for lexical tone discrimination. Nevertheless, the neural mechanisms through which hearing loss influences this process remain poorly understood. This study utilized functional magnetic resonance imaging (fMRI) to examine behavioral performance and neural activation patterns during Mandarin tone discrimination tasks in individuals with early-onset deafness. Participants included 39 individuals with early-onset deafness-categorized into a profound hearing loss group (ED1) and a moderate-to-severe hearing loss group (ED2)-along with 33 normal-hearing controls (NC). Behaviorally, tone discrimination accuracy was significantly lower in both the ED1 and ED2 groups compared to the NC group, though performance remained above chance level (25%), with the ED1 group exhibiting the lowest accuracy. fMRI results indicated that all three groups activated similar brain regions, including the bilateral superior temporal gyrus and the left inferior frontal gyrus. However, the ED1 group demonstrated significantly heightened activation in the left superior temporal gyrus (STG) and Heschl's gyrus (HG). Further analyses revealed a positive correlation between the activation intensity in these regions and air conduction hearing thresholds, yet no significant association was observed with behavioral performance, indicating constrained neural compensation following auditory deprivation. These results highlight the differential effects of hearing loss severity on tone discrimination and suggest that individuals with profound hearing loss recruit stronger auditory cortex activation to sustain basic tone processing. The findings offer novel insights into neural plasticity in the context of auditory deprivation and underscore the potential of integrating multisensory training into future hearing rehabilitation programs to enhance compensatory effectiveness.