The role of high-frequency hearing in age-related speech understanding deficits.

An experiment was conducted to further explore the effect of ageing on speech understanding under degraded listening conditions. Two groups of subjects, aged 20-39 years and 50-75 years were tested. Measurements were made of hearing thresholds in each ear from 0.25-10kHz, consonant discrimination in quiet and continuous speech spectrum noise (S/N= -10 dB) and monophonic and stereophonic frequency selectivity. Neither group would have been diagnosed as hearing-impaired. Nonetheless, the older group had significantly higher hearing thresholds, which increased systematically with frequency. Poorer consonant discrimination in noise was observed for the older group. This outcome was correlated with high-frequency thresholds, not with age. There was no between-group difference in stereophonic frequency selectivity, minimizing the possibility of age-related changes in central auditory processing. Monophonic frequency selectivity, an index of cochlear processing, was correlated with speech understanding. The results support the conclusion that observed age-related effects are secondary to cochlear dysfunction.