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Help on cochlea model.............
Would you please give us some advice or comments on this model?
"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
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
-Yadong Toward a Man-made Brain
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Dept of Electrical & Computer Engineering
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