Modeling temporal and compressive properties of the normal and impaired auditory system

Three modifications of a psychoacoustically and physiologically motivated p rocessing model [Dan et al., J. Acoust. Soc. Am. 102 (1997a) 2892-2905] are presented and tested. The modifications aim at simulating senisorineural h earing loss and incorporate a level-dependent peripheral compression whose properties are affected by hearing impairment. Model I realizes this differ ence by introducing for impaired listeners an instantaneous level-dependent expansion prior to the adaptation stage of the model. Model 2 and Model 3 realize a level-dependent compression with time constants of 5 and 15 ins, respectively, for normal hearing and a reduced compression for impaired hea ring. In Model 2, the compression occurs after the envelope extraction stag e, while in Model 3, envelope extraction follows compression. All models ac count to a similar extent for the recruitment phenomenon measured with narr ow-band stimuli and for forward-masking data of normal-hearing and hearing- impaired subjects using a 20-ms, 2-kHz tone signal and a 1-kHz-wide bandpas s noise masker centered at 2 kHz. A clear difference between the different models occurs for the processing of temporally fluctuating stimuli. A modul ation-rate-independent increase in modulation-response level for simulating impaired hearing is only predicted by Model I while the other two models r ealize a modulation-rate-dependent increase. Hence, the predictions of Mode l 2 and Model 3 are in conflict with the results of modulation-matching exp eriments reported in the literature. It is concluded that key properties of sensorineural hearing loss (altered loudness perception, reduced dynamic r ange, normal temporal properties but prolonged forward-masking effects) can effectively be modeled by incorporating a fast-acting expansion within the current processing model prior to the nonlinear adaptation stage. Based on these findings, a model of both normal and impaired hearing is proposed wh ich incorporates a fast-acting compressive nonlinearity, representing the c ochlear nonlinearity (which is reduced in impaired listeners), followed by an instantaneous expansion and the nonlinear adaptation stage which represe nt aspects of the retro-cochlear information processing in the auditory sys tem. (C) 2001 Published by Elsevier Science B.V.