Masking of short stimuli by noises with spiked spectra: I. Compressive nonlinearity of cochlea and evaluation of frequency resolution

A psychoacoustic method for measuring masking thresholds based on the application of single-type stimuli and maskers intended for revealing compressive nonlinearity of displacements of the cochlea basila membrane and evaluation of the frequency resolution of hearing in a narrow frequency range near the central frequency of the stimulus is considered. High-frequency pulses with an envelope in the form of a Gaussian function with a sinusoidal filling with the frequency band corresponding to the width of the critical hearing band have been used as stimuli (referred to as compact). Noises with a spike structure of the amplitude spectrum with a limited frequency band width served as maskers. With the central frequencies of stimuli and maskers being equal, a band noise with the central frequency corresponding with a spike of an indented spectrum was called an on(rip)-frequency masker, while that with the central frequency corresponding to a dip in an indented spectrum was called an off(rip)-frequency masker. The central frequencies and frequency bands of the stimuli and maskers were 4 kHz and 1000 Hz, respectively. The spike (dip) frequencies of an indented amplitude spectrum of a masker were 1000 Hz. In the case of successive and simultaneous masking, the dependences of the thresholds of off(rip)-frequency masking of compact stimuli on the masker level revealed compressive nonlinearity of basila membrane displacements. However, threshold on(rip)/off(rip)-frequency masking differences visualized it much better. The estimates of the frequency resolution obtained under conditions of simultaneous masking of compact stimuli during variations in the frequency of spikes of indented masker spectra of low and medium levels corresponded to the width of the critical hearing band measured using a classical method of tone masking by a pair of narrow-band noise maskers. Within the spike frequency range of 500–2000 Hz, the steepness of the dependence of off(rip)-masking of compact stimuli on the spike frequency decreased with an increase in masker levels that pointed to an effect of compressive properties of basila membrane displacements on this parameter.