Level dependence of psychophysical frequency resolution and auditory filter shape

From gated tone thresholds measured in the presence of "comb-filtered" (sinusoidal energy spectrum) noise maskers, the shape of the "auditory filter" was estimated in five frequency regions, 0.5, 1, 2, 4, and 8 kHz, at a number of masker levels. The auditory filter shape became wider, asymmetrical, and shifted towards lower frequencies as the level increased, for filters with center frequencies in excess of 1 kHz. The assumptions inherent in the derivation of the filter functions are discussed, and it is concluded that the likely deviation from these assumptions (in particular, as a result of the generation of nonlinear distortion products) leads to only small errors in the shapes of the derived filter functions.