On the relation between peripheral compression and the growth of loudness

This presentation reviews similarities and differences between normal listeners' pure-tone loudness functions and the compressive basilar-membrane, BM, input-output function. Loudness matches between pure tones and multitone complexes with widely separated components reveal that the loudness function can be modeled by a modified power function with local exponents around unity near threshold and 0.2 at moderate levels [S. Buus et al., J. Acoust. Soc. Am. 104, 399–410 (1998)]. Loudness matches between short and long tones show that the SPL difference at equal loudness is a nonmonotonic function of SPL and is largest at moderate levels [S. Buus et al., J. Acoust. Soc. Am. 101, 669–680 (1997)]. These data can be explained by a loudness function that is flattest at moderate levels, where its local exponent also is around 0.2. This value is close to that obtained for BM input-output functions. The steepening of the loudness function at low levels is qualitatively similar to BM measurements. The steepening at high levels is absent in BM data when the state of the animals' cochleae is carefully controlled. One possible explanation is that the cochleae of normal adult listeners are in worse condition than those of carefully treated animals. [Work supported by NIH/NIDCD.]