Effects of aging on amplitude-modulation following response.

Phase spectral analysis as developed by Fridman (1982) was used to detect amplitude-modulation following response (AMFR). The threshold of AMFR was determined with greater sensitivity and accuracy by phase spectral analysis than by visual analysis. Using this method, a modulation frequency (MF) of 80 Hz was found optimal for detecting AMFR in young children (ranging in age from 2 to 4 years) during sleep, for whom there is no advantage in recording 40-Hz steady-state responses. To determine the optimal MF for detecting AMFR during sleep in children less than 2 years of age and age limitation for using 80-Hz MAFR in objective audiometry, AMFR as a function of MF was investigated during sleep in 25 children with normal hearing ranging from 4 months to 15 years of age, and 10 normal hearing adults. The stimulus was a 1000 Hz, 50 dBnHL sinusoidally amplitude modulated tone with a modulation depth of 95%. MF was varied from 20 to 200 Hz in 20 Hz steps. Response was determined by phase spectral analysis and the S/N ratio calculated by spectral amplitude at the modulation frequency and noise level around the modulation frequency using fast Fourier transform. Phase spectral analysis showed AMFR at MF of 80 Hz to be the most stable and reliable in all children during sleep among MFs from 20 to 200 Hz. Spectral amplitude analysis demonstrated 80-Hz AMFR to have a high S/N ratio in all children.(ABSTRACT TRUNCATED AT 250 WORDS)