A neural-counting model based on physiological characteristics of the peripheral auditory system. V. Application to loudness estimation and intensity discrimination

Abstract

s-The psychophysical properties of a multiple-channel neuralcounting model are investigated. Each channel represents. a peripheral afferent fiber (or a group of such fibers) and consists of a cascade of signal-processing transformations, each of which has a physiological correlate in the auditory system. The acoustic signal (which may be a pure tone or Gaussian noise) is passed by our mathematical construct through the following series of transformations: an outer-and middle-ear transmission function, an inner-ear multiple-pole linear-filter tuning mechanism, a nonlinear receptor saturation function, and a refractoriness-modified Poisson transduction mechanism (which leads to a sub-Poisson neural spike count). Spontaneous neural activity is independently incorporated into each channel by means of an additive refractoriness-modified Poisson process. A union process at a more distal center in the nervous system is generated by a parallel collection of such channels with a density (in frequency) determined by the cochlear mapping function. The statistics of the union count (in a fixed time) are then processed at a decision center in a manner that depends on the psychophysical paradigm under consideration. This random count number is assumed to contain all of the information for the examples we consider. Our model has been used to calculate psychophysical functions for the following paradigms: pure-tone loudness estimation, pure-tone and variable-bandwidth noise intensity discrimination, and variable-bandwidth noise loudness summation. The theoretical results, which are determined in large part by spread of excitation, are in good agreement with human psychophysical data, provided that the parameters of the theoretical model are appropriately chosen. It has been found that a suitable choice of parameters is both physiologically sensible and self-consistent. As a further indication of the consistency of the model, the same general parametric dependencies as neurophysiological isointensity contours for peripheral afferent fibers in the squirrel monkey are exhibited by the single-channel theoretical count mean, which is calculated as a function Manuscript .of stimulus level and frequency. The single-channel count mean-to-variance ratio is in accord with laboratory data. Finally, the roles of the various components comprising our theoretical system are discussed, and our model is compared with related constructs.

Rate responses of auditory nerve fibers to tones in noise near masked threshold

“…The activity of fibers with BF's sufficiently different from the tone frequency does not change when the tone is presented, giving D values of 0 and reducing the group-average D if the activity of responsive and nonresponsive fibers cannot be separated. This view is generally consistent with population models of auditory psychophysi½s (Siebert, 1968;Lachs et al, 1984;Teich and Lachs, 1979).…”

Loudness constancy with varying sound source distance

“…This psychophysical relationship, which forms the basis of the Sone loudness scale 1 , is thought to be largely a result of processing done early in the auditory pathway. This hypothesis is supported by the success of computational models based on auditory nerve spike counts, which are roughly proportional to sound intensity at the ear, in predicting loudness/ intensity psychophysical functions [3][4][5][6] .…”

The effect of center frequency and bandwidth on the auditory evoked magnetic field

“…The idea that loudness is simply proportional to the total number of action potentials Wred by all auditory nerve neurons (the spike count hypothesis) have been investigated in animal studies. The spike count hypothesis was tested and justiWed that the rate-of-growth of both loudness and the auditory nerve spike count agreed over a wide range of tone intensity (Zwislocki, 1965;Goldstein, 1974;Lachs et al, 1984). However, disagreement also exists (Pickles, 1983;Relkin and Doucet, 1997).…”