Differential age effects for components of the adult auditory middle latency response.

The middle latency components of the auditory evoked response were obtained from a young (20-24 years of age) and an older (51 to 71 years of age) group of normal-hearing, healthy female subjects. Recording procedures and stimulus repetition rates were chosen to promote the resolution of both Pa and Pb. The absolute and peak-to-peak amplitudes of Pa and Pb were significantly larger for the older subjects at all stimulus rates. An amplitude reduction of Pb with increasing stimulus rate was much more pronounced for the young than for the older subjects. This, combined with a shorter latency for Pb in the older subjects, may have contributed to partial and/or complete fusion of Pa and Pb observed in 10 of the 17 older subjects. An apparent positive shift in the response baseline for older subjects also may have contributed to the age-related amplitude effects.