The Cortical Neural Processing for Spectrally Different Speech Sounds in Individuals with Cochlear Hearing Loss

Abstract

The Auditory Late Responses (ALLRS) is reported to test the integrity of the auditory system and it also provides a tool to investigate the neurophysiological processes that underlie our ability to perceive speech (Purdy, Katsch and Sharma, & Dillon, 2001). The development of such electrophysiological measures such as ALLRS is important because they can be used to evaluate the benefits of hearing aids and cochlear implants in infants, young children, and adults those who do not cooperate for behavioral speech discrimination testing. In the current study ALLRSs were recorded using three different speech sounds, which together covered a range of frequencies across the speech spectrum. It was determined whether it could be differentiated from each other based on response latency and amplitude measures. ALLRSs were recorded from 32 ears of 16 subjects with normal hearing adults and 23 ears of 12 adult subjects with cochlear hearing loss for three different speech sounds at 40dB SL and 70 dBnHL. ALLRS waveforms were reliably elicited by each of the speech sounds in all participants in both normal hearing and cochlear hearing loss individuals. Each of the speech sound elicited different ALLRS waveforms. The results suggest that neurophysiological processes are different for different speech sounds. Longer latency for /da/ suggests that the processing at the cortical center is different depending on the frequency composition of the signal. A significant difference between the groups for latency and amplitude of ALLRSs for all the three speech sounds at each presentation level suggests that speech processing is altered in individuals with cochlear hearing loss.