Effects of age on modulation masking patterns for different shapes of masker waveforms

Modulation-rate selectivity, measured using a modulation-masking paradigm, has been shown to be differentially affected by advancing age (reduced modulation selectivity) and age-related hearing loss (increased modulation selectivity). In this study, we systematically explored the relationship between modulation masking patterns and age-related loss of cochlear nonlinearity. The study compared modulation masking for younger (18–30 years) and older (55–75 years) adults with clinically normal hearing for frequencies up to 4 kHz. Modulation masking patterns were measured for different shapes of modulation masker waveforms: sinusoidal, ramped and damped, and two modulation waveforms with the magnitude spectrum of a rectangular modulation but different phase spectra. The non-sinusoidal masker shapes were chosen to test the generalizability of the modulation power spectrum model. The signal was sinusoidal amplitude modulation (SAM) with modulation rates at and around the masker frequency. The modulating waveforms were applied to a noise carrier lowpass-filtered at 4 kHz. Loss of cochlear nonlinearity was estimated using the growth of distortion-product otoacoustic emissions. We found that the effects of age and strength of cochlear nonlinearity on modulation masking depend on the modulation rate and the shape of the masker waveform. [Work supported by NIH R01 DC 021362 (Wojtczak)]