Brainstem and Cortical Responses to Speech Stimuli in Individuals with Cochlear Hearing Loss

Abstract

This study investigated the effect cochlear pathology on brainstem and cortical responses to speech burst and transition. The relationship between these potentials and speech identification scores was also investigated. Ten adult subjects with cochlear pathology and 12 age matched normal hearing subjects were included in the study. Burst and transition portions were extracted separately from the stimuli /pa/, /ta/, /ka/. Burst evoked brainstem responses were analyzed for wave V, transient evoked brainstem responses were analyzed for peak V, A, C, D, E and F and cortical evoked potentials were analyzed for P1, N1, P2 and N2. Speech identification scores in quiet and in the presence of noise were obtained for bisyllabic word list in Kannada. Burst evoked responses showed a significant difference between the latency of wave V obtained in subjects with cochlear hearing loss and those with normal hearing group but no significant difference was found in terms of wave V amplitude. For the transition stimuli, latencies of wave V, A, C, D, E, and F as well as the amplitude of wave V were significantly different between the two groups. All the components (V, A to F) evoked by transition stimuli significantly correlated with SIS scores in noise. But no correlation was observed for burst evoked brainstem responses. There was no significant difference between groups for all the components of LLR (P1, N1, P2 & N2) but N1-P2 amplitude was significantly different between the groups. These findings suggest that cochlear hearing loss impairs the processing of the burst and transition portion of speech signal mainly at the brainstem level.