Is there anyone who would verify my code about filtering the fNIRS data?
hello,
my name is anna lee and my major is based on Human-Computer Interaction.
We use the Sectratech OEG-16 (fNIRS device) to analyze the relative change in hemoglobin levels.
To filter the raw data, we referenced many articles and built a matlab code with following procedure.
1.To eliminate the trends and do the DC offset,
we use the detrend function.
2. To eliminate the motion effects, do the Common average reference(CAR)
: (raw data - the total average of data)
3. Band-pass filtering (LPF 0.1hz/ HPF 0.01hz)
however, i am not sure whether i did right or not...
it would be much helpful if anyone would verify my code or give some comments
(i attached the matlab code)
Thansk :)
Hi,
There is an error in data filtering section. It is not possible to synthesize a Butterworth band-pass filter of such a low order. You can use an optimal elliptic filter, for example:
Wn = [0.01 0.1];
Fs = 1.53; Fn = Fs/2;
N = 5; Rp = .5; Rs = 50;
[b,a] = ellip(N,Rp,Rs,Wn/Fn);
You can see the magnitude and phase response of the filter using Matlab's fvtool:
fvtool(b,a);
Best regards,
Rosen
I am not sure of why do you want to low-pass with a 0.1 Hz. It might remove much of your useful signal (depends also on your paradigm tough)
To eliminate the motion effects, its better to use wavelet transform. you may refer to http://www.ncbi.nlm.nih.gov/pubmed/22273765
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