Psychophysical estimates of nonlinear cochlear processing in younger and older listeners.

The primary goal of this project was to compare the performance of younger and older listeners on a number of psychophysical measures thought to be influenced by nonlinear cochlear processing. Younger (mean of 25.6 years) and older (mean of 63.8 years) listeners with normal hearing were matched (within 5 dB) according to their quiet thresholds at the two test frequencies of 1200 and 2400 Hz. They were similarly matched at the adjacent octave frequencies of 600 and 4800 Hz (within 5 dB at one and 9 dB at the other). Performance was compared on measures of auditory filter shape, psychophysical suppression, and growth of forward masking. There was no difference between the two age groups on these psychophysical estimates reflecting nonlinear processing, suggesting that aging per se does not affect the cochlear nonlinearity, at least for the ages sampled here. The results did, however, consistently demonstrate an age-related increase in the susceptibility to forward masking.