Instantaneous frequencies (IFS)
http://sciencestage.com/d/286699/3d-eeg-rhythm-mapping-durin...
These EEG signals were filtered for the alpha band (8.0-14.0 Hz) using a fast Fourier transform-based digital filter. From thresholded zero-crossing points, periodic intervals of the alpha waves were determined and converted to instantaneous frequencies (IFs).

http://www.google.com/search?hl=en&client=firefox-a&hs=0W3&r...

http://www.google.com/search?hl=en&client=firefox-a&rls=org....

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Note added at 1 day7 hrs (2010-04-30 09:55:00 GMT)
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http://en.wikipedia.org/wiki/Time–frequency_analysis
In signal processing, time–frequency analysis is a body of techniques for characterizing and manipulating signals whose statistics vary in time, such as transient signals.
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Finding instantaneous frequency
The definition of instantaneous frequency is the time rate of change of phase, ...
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Biomedical engineering
One can use time–frequency distribution to analyze the electromyography (EMG), Electroencephalography (EEG), or otoacoustic emissions (OAEs).

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Note added at 1 day7 hrs (2010-04-30 10:02:47 GMT)
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http://en.scientificcommons.org/35919591
This paper presents a method for estimating the instantaneous frequency (IF) of multicomponent signals. The technique involves, firstly, the transformation of the one-dimensional signal to the two-dimensional time-frequency (TF) domain using a reduced interference quadratic TF distribution. IF estimation of signal components is then achieved by implementing two image processing steps: local peak detection of the TF representation followed by an image processing technique called component linking. The proposed IF estimator is tested on noisy synthetic monocomponent and multicomponent signals exhibiting linear and nonlinear laws. For low signal-to-noise ratio (SNR) environments, a TF peak filtering preprocessing step is used for signal enhancement. Application of the IF estimation scheme to real signals is illustrated with newborn EEG signals. Finally, to illustrate the potential use of the proposed IF estimation method in classifying signals based on their TF components' IFs, a classification method using least squares data-fitting is proposed and illustrated on synthetic and real signals.