Loudness of dynamic stimuli in cochlear-impaired listeners

Abstract

In normal hearing listeners, a temporally fluctuating sound with modulating frequencies from 4 to 400 Hz was found to be louder than predicted by its averaged power. The louder sensation due to temporal fluctuation was also found to be overall level-dependent: approaching peak amplitude loudness at a comfortably loud level, becoming less at lower sensation levels, and disappearing at higher levels. If this level-dependent loudness effect were related to the nonlinear cochlear compression, then it would disappear in cochlear-impaired listeners because their nonlinear compression is presumably damaged. Three listeners with clinically diagnosed cochlear impairment balanced loudness between white noise and sinusoidally amplitude-modulated noise. The results showed that the modulated noise was louder for modulating frequencies between 4 and 400 Hz at all three sensation levels, consistent with the hypothesis that the overall level effect on loudness of dynamic stimuli is related to the cochlear compression. These results indicate that loudness of dynamic stimuli is governed by two different mechanisms: a retrocochlear temporal processing mechanism which is presumably preserved in both normal and cochlear-impaired listeners, and a cochlear mechanism which provides amplitude compression at high levels in normal listeners and is damaged in the cochlear-impaired listeners. [Work supported by NIDCD.]