Nonlinear Effect Of Hearing System To Noise Signal

Auditory system is a complex nonlinear system, usually processing and analyzingnoisy auditory signals. The nonlinear mechanism to process noisy signals of auditorysystem is an important scientific subject, which is also a critical issue for auralrehabilitation and speech signal processing. However, for the sake of the complexity ofthose nonlinear properties, it still remains an open and challenging question.In this dissertation, the role of noise in the auditory system is explored. For thispurpose, the nonlinear property of the mechanoelectrical transduction of inner hair cell isdiscussed firstly. A dynamics model is established by a modified sigmoid function, whichdescribes the transduction of the corresponding electrical response from the displacementof the hair bundle. It was discovered that adding noise can improve the transduction whenthe stimulus is so strong that the transduction function is at saturation transducing region.The similar phenomenon was also discovered in an IF neuron model. Our resultsdemonstrate that noise could also be beneficial to suprathreshold signals.Many researches imply that noise could be beneficial for auditory signals which arelimited to sub-threshold and saturation situations. However, it is found that noise could bebeneficial to stimuli without amplitude limit when noise inputted with signal and noise atthe threshold are both concerned in an IF neuron model. The result implies that the innernoise in the auditory system is probably beneficial to noisy stimuli without amplitudelimit.At the end, an auditory processing model is established by integrating some auditory nonlinear processing steps. The model is stimulated by a recorded vowel pronunciation，and the firing rate is considered as a measurement of the output. As the stimulus is noisy, itdemonstrates that the intensity of input noise rarely affect the firing rate of output. Thisresult implies that this nonlinear auditory processing model is anti-noise.The results of this dissertation imply that the anti-noise property of the auditorysystem is relative to the nonlinear properties of the auditory system. This reveals newinsight into the mechanism of auditory processing, and is beneficial for establishingnonlinear signal processing systems or improving cochlear implant technologies.