Subject: Help on cochlea model............. From: Yadong Wang <ydwang(at)ELE.URI.EDU> Date: Wed, 17 Jan 2001 22:40:54 -0500Hi there, Would you please give us some advice or comments on this model? Thanks! "It is natural to wonder how the auditory system of humans and animals represents and processes time-varying signals in the audible range of frequencies and make inferences on them. The acoustic energy from various sound sources impinges on our ears from different directions and the inner ears and the brain, together, seem to separate them into different streams, enabling us to parse a complex superposition of many overlapping broad-band, non-stationary signals into independent recognizable constituents. What kind of signal processing underlies this phenomenon? Significant physiological and psychophysical evidence points to the fact that the inner ear and the auditory centers in the brain, in addition to performing some form of spectral analysis, also extract temporal modulation information from the acoustic signals. This information is encoded in the timing patterns of the spike trains that originate in the inner ear. With the help of auditory scientists we translate the above observations into mathematically tractable signal processing problems. Specifically, we explore the following basic question: how can band-pass signals be represented by timing information} only, as opposed to traditional Nyquist-rate amplitude sampling (as in Shannon's sampling theorem)? Our recent results indicate that the information about the phase and envelope modulations of arbitrary band-pass signals can be represented by certain zero-crossings alone (not those of the signal), if appropriate adaptive preprocessing (demodulation) is performed on the signal. Based on these ideas we propose to develop analysis-synthesis procedures in which time-varying signals such as speech can be effectively represented by a small number of modulated components using only timing information. Overall our approach is a non-parametric way to characterize modulation properties of signals. The potential applications include improved feature extraction for recognition/classification, separation of overlapping sounds, source localization etc. In addition, the proposed analytical tools might be helpful to the auditory scientist in explaining some of the unexplained nonlinear phenomena observed in the auditory periphery. More recently, we noticed that the above results are closely related to representing envelope and phase modulations of a bandpass signal by certain zero-crossings. These results can be used to represent time-varying signals almost exclusively by using timing information. This again has similarities to representing signals by spike-trains in biological systems. If interested, you could see our new unpublished paper at http://www.ele.uri.edu/~ydwang/Jasa.pdf -Yadong Toward a Man-made Brain ___________________________________________ 401-874-5392 (O) Leave Msg Please... 401-789-7742 (H) Dept of Electrical & Computer Engineering HTTP HomePage http://www.CoZeC.com