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EEG: brainwave generation, questions

Friso Westerhuis westerhuis at nici.kun.nl
Fri Feb 2 07:40:16 EST 1996


(Hypnotics) wrote:
>
>Also, it seems accepted that brainwaves can be broken down into their
>component sine waves by fourier transform, but what evidence is there that
>brainwaves ARE sinusoidal?  What evidence shows that brainwaves cannot
>REALLY be sawtooth in some instances, square in others etc.  Are we
>creating an artificial construct?

The Fourier transformation is "just" a mathematical procedure to 
transform the signal from time domain (an EEG for example) into the 
frequency domain (the spectrum). It can be demonstrated that almost any 
function can be described by a set of sines and cosines. So the use of 
cosines and sines doesn't say a thing about the physiology.
These functions are special because they are periodic and orthogonal. 
Other functions like blockwaves for exapample could also be used to 
descride a function (or a signal like an EEG).
So this transformation, by using cosines and sines does not say anything 
about the generation of an EEG. It's useful though, because the spectrum 
(the "product" of an Fourier Transform (FFT) ) contains useful 
information about the (generation of the) EEG.

A very good book about this subject is :
Paul A. Lynn
An Introduction to the Analysis of Signals and Processing of signals

Friso




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