Experimental Studies Of Pitch Perception On Auditory Periphery

Pitch is the most important perceptual feature of sound. Melody which formed by the change in pitch is the basis of music. However, the physical nature of pitch is still an open question. Moreover, it is also full of controversy that where pitch perception occurs. Initially pitch is considered to be the frequency of signal; this view is supported by the function of frequency analysis of auditory periphery but fail to explain pitch perception of complex tone contained multiple frequency components. With the development of Neuroscience, the researchers believe that the pitch perception occurs in the nervous system and pitch is some characteristics in time domain. Over the past decade, the nonlinear dynamics of cochlea reinterpret the pitch shift effect, to point out again that the auditory periphery may be involved in the pitch extraction process. Presently, there is no physiological experiment on auditory periphery to test these nonlinear dynamics theories. If the pitch perception phenomena is observed on the auditory periphery, on the one hand can enhance the understanding of pitch, on the other hand, will greatly promote the development of auditory research.As auditory systerm is sensitive to the change of pitch, psychoacoustic experiments have been the primary methods to research pitch perception. The most important phenomena of pitch perception, such as missing fundamental and pitch shift effect, are all discovered in psychoacoustic experimental studies. This dissertation is the first physiological experimental study of pitch perception on the auditory periphery. We began to design the measurement system for cochlea in2009, and presented a scheme of heterodyne interferometer based on direct time interval measurement. In order to meet the requirements of high resolution and linearity, we proposed a novel phase demodulation method to convert dynamic phase measurement to the continuous measurememt of time interval and introduced time-to-digital converter to measure time intervals.After two years elaborate preparation, the high resolution heterodyne interferometer based on time-to-digital converter was completed in2011. The results of performance tests confirmed that the recorded vibration of interferometer is less than0.5nm and the interferometer has better linearity than the traditional phase demodulation method. After that, the interferometer was improved to solve some problems in pratical measurement. First, instead of the referenc optical path, a circuit module was used to generate the reference signal which is needed in phase decoding. More energe of laser were used for measurement. Then, a splitting ratio adjustor was used to enhance the signal to nosie ratio of optical system. After optimizing the splitting ratio, the interferometer can measure object with faint reflection (0.01%). Finally, a microscope was intergrated with interferometer to form a system which could faithly record the resopse of live cochlea under sound stimulus. Based on the cochlear vibration measurement system, some physiological experiments about pitch perception were completed on auditory periphery. We did not found resonance spectral line of three frequency resonce. And the pitch shift effect was observed on the auditory periphery if the pitch is defined by the reciprocal of time interval. The results demonstrated that the auditory periphery participates in pitch extraction process. The physical nature of pitch is preferred to be some information in time domain.This work is supported by the National Natural Science Foundation of China (Grant No60874099) and "Cognitive Computing of Visual and Auditory Information" of NSFC (Grant No90820001).