Cortical compensation for hearing loss, but not age, in neural tracking of the fundamental frequency of the voice
Auditory processing is affected by advancing age and hearing loss, but the underlying mechanisms are still unclear. We investigated the effects of age and hearing loss on temporal processing of naturalistic stimuli in the auditory system. We employed a recently developed objective measure for neural phase-locking to the fundamental frequency of the voice (f0) which uses continuous natural speech as a stimulus, i.e. 'f0 tracking'. F0-tracking responses from 54 normal hearing and 14 hearing impaired adults of varying ages were analysed. The responses were evoked by a Flemish story with a male talker and contained contributions from both subcortical and cortical sources. Results indicated that advancing age was related to smaller responses with less cortical response contributions. This is consistent with an age-related decrease in neural phase-locking ability at frequencies in the range of the f0, possibly due to decreased inhibition in the auditory system. Conversely, hearing impaired subjects displayed larger responses compared to age-matched normal hearing controls. This was due to additional cortical response contributions in the 38-50 ms latency range, which were stronger for participants with more severe hearing loss. This is consistent with hearing-loss induced cortical reorganisation and recruitment of additional neural resources to aid in speech perception.