MODELING AUDITORY PROCESSING OF AMPLITUDE-MODULATION .1. DETECTION AND MASKING WITH NARROW-BAND CARRIERS

This paper presents a quantitative model for describing data from modu lation-detection and modulation-masking experiments, which extends the model of the ''effective'' signal processing of the auditory system d escribed in Dau et al. [J. Acoust. Sec. Am. 99, 3615-3622 (1996)]. The new element in the present model is a modulation filterbank, which ex hibits two domains with different scaling. In the range 0-10 Hz, the m odulation filters have a constant bandwidth of 5 Hz. Between 10 Hz and 1000 Hz a logarithmic scaling with a constant (2 value of 2 was assum ed, To preclude spectral effects in temporal processing, measurements and corresponding simulations were performed with stochastic narrow-ba nd noise carriers at a high center frequency (5 kHz). For conditions i n which the modulation rate (f(mod)) was smaller than half the bandwid th of the carrier (Delta f), the model accounts for the low-pass chara cteristic in the threshold functions [e.g., Viemeister, J. Acoust. Sec . Am. 66, 1364-1380 (1979)]. In conditions with f(mod) > Delta f/2, th e model can account for the high-pass characteristic in the threshold function. In a further experiment, a classical masking paradigm for in vestigating frequency selectivity was adopted and translated to the mo dulation-frequency domain. Masked thresholds for sinusoidal test modul ation in the presence of a competing modulation masker were measured a nd simulated as a function of the test modulation rate. In all cases, the model describes the experimental data to within a few dB. It is pr oposed that the typical low-pass characteristic of the temporal modula tion transfer function observed with wide-band noise carriers is not d ue to ''sluggishness'' in the auditory system, but can instead be unde rstood in terms of the interaction between modulation filters and the inherent fluctuations in the carrier. (C) 1997 Acoustical Society of A merica.