EFFECTS OF AGING ON AMPLITUDE-MODULATION FOLLOWING RESPONSE

Phase spectral analysis as developed by Fridman (1982) was used to det ect amplitude-modulation following response (AMFR). The threshold of A MFR was determined with greater sensitivity and accuracy by phase spec tral 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 th ere is no advantage in recording 40-Hz steady-state response. To deter mine the optimal MF for detecting AMFR during sleep in children less t han 2 years of age and age limitation for using 80-Hz MAFR in objectiv e audiometry, AMFR as a function of MF was investigated during sleep i n 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 dBn HL sinusoidally amplitude modulated tone with a modulation depth of 95 %. MF was varied from 20 to 200 Hz in 20 Hz steps. Response was determ ined by phase spectral analysis and the S/N ratio calculated by spectr al amplitude at the modulation frequency and noise level around the mo dulation frequency using fast Fourier transform. Phase spectral analys is showed AMFR at MF of 80 Hz to be the most stable and reliable in al l children during sleep among MFs from 20 to 200 Hz. Spectral amplitud e analysis demonstrated 80-Hz AMFR to have a high S/N ratio in all chi ldren. 80-Hz AMFR would thus appear to be useful for assessing hearing even in infants and children in their early teens, though it is not a dequate for hearing assessment in adults.