Effect of Ageing on Encoding Of Speech Signal in the Auditory System

Abstract

Composite signal such as speech processing in auditory system is one of the major processes that get influenced by systematic effect of ageing on auditory system. Even with the normal audiometric thresholds middle-aged listeners report difficulty in conversing in social environment which could be attributed to influence of ageing in throughout auditory system from cochlea, brainstem and at the central system. The current study aimed to investigate correlation of speech signal encoding between cochlea, brainstem and cortical auditory processing in normal young adults and middle aged individuals. Two groups of participants were included in the study. Group 1 (younger adults) included of 15 subjects (15 ears) age ranged between 18 to 30 years (Mean age range =25.7) .Group 2 (Middle aged adults) included of 15 subjects (15 ears) aged ranged between 45 to 60 years (Mean age range =54.2). All the participants in two groups had normal hearing sensitivity, normal middle ear function, no history of exposure to noise and no otological and neurological problems. All the participants first went through routine audiological evaluations such as pure tone audiometry, tympanometry & Reflexometry to confirm the candidacy. Later for all the participants in two groups, Speech evoked ABR and Speech evoked late latency responses were recorded. Results revealed a reduction in encoding of fundamental frequency and first formant frequency encoded at brainstem level in middle aged listeners compare to the younger participants. There was also a prolonged latency of P1 and increased amplitude at N1 in the auditory late latency responses in middle aged group. Thus, the results of the study indicate, that processing of composite signal such as speech get influenced by the ageing which needs routine evaluations in middle aged individuals.