Masking of short stimuli by noises with spiked spectra: II. Time summation and frequency selectivity of hearing in a narrow frequency range |
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Authors: | L K Rimskaya-Korsakova M R Lalayants A Ya Supin G A Tavartkiladze |
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Institution: | 1.Andreev Acoustics Institute,Russian Academy of Sciences,Moscow,Russia;2.Russian Scientific Practical Center of Audiology and Hearing Aid,Moscow,Russia;3.Sevetsev Institute of Ecology and Evolution Problems,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | The thresholds of masking of short high-frequency pulses with either different durations (1.25–25 ms) and similar central
frequency or different central frequencies (3.6–4.4 kHz) but similar durations were measured to reveal manifestations of the
properties of peripheral encoding in auditory perception. Noises with a spiked amplitude spectrum structure were used as maskers.
The central frequency and the frequency band of a masker were 4 and 1 kHz, respectively. The central frequencies of a stimulus
and a masker being equal, the noise the central frequency of which coincided with the frequency corresponding to a dip of
an indented spectrum was called an off(rip)-frequency masker. Owing to the off(rip)-masker, stimuli-induced masking thresholds were formed taking into account excitation in a narrow region of a basila membrane
and auditory nerve fibers with characteristic frequencies from a narrow range. High-frequency pulses with an envelope in the
form of the Gaussian function and sinusoidal filling were used as stimuli. At masker levels of 30 dB above the auditory threshold,
frequencies of off(rip)-masker spectra spikes of 500–2000 Hz, and a central stimulus frequency of 4 kHz, the thresholds of tonal stimuli (25 ms in
duration) masking in two out of three probationers were higher than the thresholds of masking of compact stimuli (1.25 ms
in duration). In the third probationer, on the contrary, the thresholds of tonal stimuli masking were lower than the thresholds
of compact stimuli masking. At masker levels of 50 dB, individual threshold differences disappeared. The obtained results
were interpreted in the context of implementation of different methods of auditory encoding of the intensity. The methods
were based on either the average frequency of auditory nerve pulsations or the number of fibers participating in the response.
The interpretation was also carried out in the context of revealing manifestations of nonlinear properties of basila membrane
displacements in auditory thresholds. The fact that the dependence of detection thresholds of compact stimuli on their central
frequency in one of the two probationers did not reveal the minimum in case of coincidence of off(rip)-masker and stimulus frequencies pointed to the presence of an auditory “problem zone” that was likely to be localized at
the periphery of the auditory system. |
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