Degenerative changes associated with ageing may affect processing of spectral and temporal cues in speech at cortical and subcortical levels, even though these individuals may have normal audiometric thresholds. These changes are more likely to be picked up by speech evoked ABR than conventional ABR using click stimuli. In this study a comparison was made between 25 young individuals and 25 elderly subjects, all with normal hearing. Click evoked ABR showed delayed latencies and reduced amplitude in the elderly group, particularly for wave V. More complex measurements were also undertaken, namely onset (peaks V and A), frequency following response (peaks D, E and F) and offset response. Upon introduction of noise, these appeared severely degraded in the geriatric group. The findings clearly suggest age-related alterations in subcortical neural encoding of speech leading to poor speech discrimination in elderly subjects. Speech evoked ABR further elicited reduced synchronous neural activity in this group, especially in noisy conditions. These characteristics may also apply to autism spectrum disorder and persons with learning disabilities. More studies are required in this field to develop effective auditory diagnostic and rehabilitation strategies for the elderly population and also those with autism and learning difficulties who have speech discrimination problems.
Effects of age on neuro-physiological processing of speech at brainstem level
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