AUDITORY FILTER NONLINEARITY AT 2 KHZ IN NORMAL-HEARING LISTENERS

Auditory filters broaden with increasing level. Using a recently devel oped method of fitting filter shapes to notched-noise masking data tha t explicitly models the nonlinear changes in filter shape across level , results at 2 kHz from 9 listeners over a wide range of levels and no tch widths are reported. Families of roex(p,w,t) filter shapes lead to models which account well for the observed data. The primary effect o f level is a broadening in the tails of the filter as level increases. In all cases, models with filter parameters depending on probe level fit the data much better than masker-dependent models. Thus auditory f ilter shapes appear to be controlled by their output, not by their inp ut. Notched-noise tests, if performed at a single level, should use a fixed probe level. Filter shapes derived in this way, and normalized t o have equal tail gain, are highly reminiscent of measurements made di rectly on the basilar membrane, including the degree of compression ev idenced in the input-output function. (C) 1998 Acoustical Society of A merica.