Peripheral basis of auditory discrimination of changes in the intensity of pulsed sounds presented in silence and after noise exposure

Causes of deterioration and facilitation of discrimination of changes in the intensity of short high-frequency sounds (pulses) presented in silence, with noise, and after noise exposure were analysed by comparing the results of simulation and psychoacoustic experiments. In the simulation experiments we studied the characteristics of peripheral coding of changes in the intensity of pulses; searched for the conditions when the response of the ensemble can store information about the amplitude-temporal structure (conditions for the implementation of the volley principle); and analysed the statistical characteristics of responses of the ensemble of auditory nerve fibres (ANF) to pulse and composite sound containing long noise masker and pulse (“noise–pulse complex”). Coding should be understood as the conversion from the analogous receptor potential of the inner hair cell to the sequence of action potentials (spikes) generated by the ensemble of ANFs. Simulation experiments have shown that changes in masker level may cause changes in the properties of peripheral coding of both pulse and noise–pulse complex. Auditory experiments have shown that an appreciable effect of discrimination improvement occurs when the average intensity pulse is presented along with or after the noise masker, the level of which is almost equivalent to the threshold of pulse masking. Furthermore if the delay between pulse and end of masker is 50–60 ms, increase in the masker level causes alternation of the effects of deterioration and facilitation of discrimination of changes in the pulse intensity. There are grounds for believing that the observed effects are based on the variability of properties of the peripheral coding of both pulses and noise–pulse complexes.