Experimental Studies Of Pitch Perception In Vitro Cochlea

Pitch is one of the three most important features of sound including loudness, timber. But so far, where pitch perception occurs and mechanism of pitch is still a question. Early auditory periphery studies believed that fundamental frequency determines the pitch of periodic signal. The later neuroscience researches have proposed that the pitch of complex sound which comes from central nervous system reflected the time domain features. Over the past decade, with the development of the nonlinear dynamics of cochlea, it is proposed again that the auditory periphery may be involved in the pitch generating. But there is no physiological experiment on auditory periphery to test these nonlinear dynamics theories. Once the pitch is observed on the auditory periphery, especially the second pitch shift, which is the most complex part of the pitch perception phenomena, it can enhance the understanding of pitch perception mechanism; also, it will greatly promote the development of cochlea implant. Supported by the National Natural Science Foundation of China, for the first time, we study pitch perception in cochlea. We focused on the second pitch shift on the auditory periphery based on our group previous research.We used a more stable frequency He-Ne laser and we also strictly tested nonlinearity of the heterodyne laser interferometer based on TDC linear to guarantee the accuracy and reliability of the experimental data. After we learned the physical structure of the cochlea and structure in guinea pigs, we explored new minimally invasive surgical exposure of the cochlea, we inserted the trachea, removed a small area of the frontal bone to supply blood for venous and arterial blood and to treat wounds flexibly. Then we produced the new jigs to fix the position of guinea pigs, homemade instruments playing 200 ?m hole in the live guinea pig cochlea. Such a minimally invasive surgery is simple and less damage, providing possibility of vivo measurements. Based on the above work, we observed the basilar membrane vibration of in vitro cochlea which is still active, and we also successfully observed nonlinear phenomena in cochlear. In the end, according to psycho-acoustic pitch shift experiments, we designed the second pitch shift experiment by heterodyne laser interferometer; we finally succeed in measuring different frequency second pitch shift on basilar membrane in vitro cochlea which is still active. The results are consistent with the psychological experiments and the results demonstrated that the auditory periphery participates in pitch extraction process.Experiments also show the existence of combination tone existence when pitch shift happens. When combination sounds disappear, the second pitch shift also disappears. It proposes the mechanism of pitch generation to some degrees.