Stimulus variability and auditory filter shape

Abstract

The way in which stimulus variability affects the attenuation characteristic or auditory filter shape inferred from masking experiments was investigated in humans. Stimulus variability had a pronounced effect on filter shapes derived from bandlimiting experiments in which the signal is a tone, the masker is a band of noise centered on the tone and the independent variable is the width of the noise band; no effect was observed on filters obtained from notched-noise masking experiments. To extent the utility of the filter-shape concept, an experiment in which the masker is 2 tones rather than noise was replicated. The tones, each 57 dB SPL [sound pressure level], were used to mask a narrow band of noise centered midway between them; threshold for the noise signal was measured as a function of the frequency separation of the tonal maskers. The data is in good agreement with the auditory filter shape derived using a notched-noise masker and a tonal signal. To predict the absolute levels obtained in the noise-masking experiments, it was assumed that internal noise adds to the variability of the stimuli. The resulting model, which incorporates the filter shape from the notched-noise experiment and the energy detection model, predicts not only the form but also the absolute levels obtained in the bandlimiting and notched-noise experiments. It also predicts the shape of the data from the two-tone masking experiment but it does not predict the overall level.