BASILAR-MEMBRANE NONLINEARITY AND LOUDNESS

Loudness matching functions for tones for persons with one shifted-thr eshold ear (hearing loss and noise-shifted thresholds) and one ear wit hin normal limits were used to derive the presumed basilar membrane (B M) input-output (I/O) function in a normal ear. The comparison was mad e by assuming that the BM I/O function for the ear with the cochlear t hreshold shift has a slope of one (a linearized cochlea). The function for the normal ear was derived from the loudness matching function ba sed on this assumption. Comparisons were made for archival basilar mem brane data [M. A. Ruggero, N. C. Rich, A. Recio, S. S. Narayan, and L. Robles, J. Acoust. Sec. Am. 101, 2151-2163 (1997)] for chinchilla and archival loudness matches for long-duration tones for persons with va rious degrees of cochlear hearing loss [F. MIskolczy-Fodor, J. Acoust. Sec. Am. 32, 486-492 (1960)]. Comparisons were made also between BM I /O functions and ones derived from loudness matches for persons with u nilateral hearing loss simulated by broadband noise. The results show a close resemblance between the basilar membrane I/O function and the function derived from loudness matches for long-duration tones, even t hough the comparison was between human and chinchilla data. As the deg ree of threshold shift increases from 40 to 80 dB, the derived BM I/O functions become shallower, with slopes for losses of 60 dB or more fa lling in the range of values reported for physiological data. Addition al measures with short-duration tones in noise show that the slope of the loudness function and the slope of the derived basilar membrane I/ O function are associated with the behavioral threshold for the tone. The results for long-duration tones suggest a correspondence between B M displacement and loudness perception in cases of recruitment, but th e relation between the degree of loss and the amount of BM compression and the relation between signal duration and compression suggests tha t other factors, such as the neural population response, may play a ro le. (C) 1998 Acoustical Society of America.