Using Matlab FFT to extract frequencies from EEG signal

Question

I am new to BCI. I have a Mindset EEG device from Neurosky and I record the Raw data values coming from the device in a csv file. I can read and extract the data from the csv into Matlab and I apply FFT. I now need to extract certain frequencies (Alpha, Beta, Theta, Gamma) from the FFT.

Where Delta = 1-3 Hz

Theta= 4-7 Hz

Alpha = 8-12 Hz

Beta = 13-30 Hz

Gamma = 31-40 Hz

This is what I did so far:

f = (0:N-1)*(Fs/N);
plot(rawDouble);
title ('Raw Signal');
p = abs(fft(rawDouble));
figure,plot (f,p);
title('Magnitude of FFT of Raw Signal');

Can anyone tell me how to extract those particular frequency ranges from the signal?? Thank you very much!

Answer 1

For convenient analysis of EEG data with MatLab you might consider to use the EEGLAB toolbox (http://sccn.ucsd.edu/eeglab/) or the fieldtrip toolbox (http://fieldtrip.fcdonders.nl/start).

Both toolboxes come with good tutorials:

http://sccn.ucsd.edu/eeglab/eeglabtut.html

http://fieldtrip.fcdonders.nl/tutorial

Answer 2

You may find it easier to start off with MATLAB's periodogram function, rather than trying to use the FFT directly. This takes care of windowing the data for you and various other implementation details.