Analysis of nonlinear cellular dynamics in the cochlea using the continuous wavelet transform and the short-time Fourier transform

The continuous wavelet transform (CWT) and the short-time Fourier transform (STFT) are used to analyze the time course of cellular motion in the guinea-pig inner ear. The velocity responses of individual auditory cells (outer hair cells and Hensen's cells) to amplitude-modulated (AM) acoustical signals display characteristics typical of nonlinear systems, such as harmonic generation. Nonlinear effects are particularly pronounced at the highest stimulus levels, where half-harmonic, and sometimes quarter-harmonic, components are also seen. Both the CWT and the STFT are found to be useful in analyzing these velocity responses. The authors carry out CWT analyses using a Morlet wavelet and an AM wavelet, and find the results are quite similar.>