[Eeglablist] Questions about ERSP in Study design

[Benjamin Bardel]

Dear EEGLAB Community,

I’m trying to study the ERD/ERS (event related spectral pertubations) of multiple subjects in different conditions (multiple trials, epochs [-4000 1000], Fs=1000 Hz, Notch filtered) but I have some questions and I can’t find answers despite many questions asked on the list about this subject…

My questions (and solutions so far…) are : 
1 – How to extract ERSP according to Pfurscheller 
So far I did this :         
	>> [STUDY ALLEEG] = std_precomp(STUDY, ALLEEG, {}, 'interp', 'on', 'recompute', 'on', 'ersp', 'on', 'erspparams', {'cycles' [7 0.1] 'freqs' [7 23] 'ntimesout' 388 'freqscale' 'linear' 'padratio' 4 'baseline' [-3000 -2000]});  %% Compute ERSP with a baseline set between -3sec & -2sec
	>> STUDY = pop_erspparams(STUDY, 'condstats', 'on','freqrange',[]); 
	>>[ STUDY erspdata ersptimes erspfreqs pgroup pcond pinter] = std_erspplot(STUDY,ALLEEG,'plotfunc','newtimef','timerange', [],'trialbase', 'on','freqrange', [], 'channels', {'C1';'CZ';'C2';’etc….’})   
	>> ersp=erspdata{:,:,:,:}; %% change erspdata (cell) to double
	>> ersp2=(10.^(ersp/10)-1)*100;  %%  Pfurscheller’s formula of ERSP in percentage and not ERSP=10*log10(A/R) (which is the format of values given by time frequency decomposition ? )  → Is it correct? I found it on this post : https://sccn.ucsd.edu/pipermail/eeglablist/2012/004755.html 

Is this method good to extract ERSP in percentage (with 0% the value at Baseline) ? Is it the format of values in the variable ‘ersp2’ ? I’m a bit lost between log, linear and std format of the data given by the time-frequency decomposition in EEGLAB Study design….
There is an other post about that : https://sccn.ucsd.edu/pipermail/eeglablist/2013/006061.html.  I’m not sure what is the format of the data (standard deviation of log-transformation ?)

	>> S1ersp=ersp(:,:,:,1); %%extract data for S1
	 >> S2ersp=ersp(:,:,:,2); %% extract data for S2
	>> idxfreqalpha=find(erspfreqs>=7 & erspfreqs <= 13); % alpha band between 7-13 Hz
	>> idxfreqbeta=find(erspfreqs>=16 & erspfreqs <= 21); 
	>> idxtime=find(ersptimes >= -2000 & ersptimes <=400); %% Analyze ersp between -2 seconds and +400ms
	>> timex=ersptimes(ersptimes>= -2000 & ersptimes<=400); 
             
2- Is there a faster way (or better) to Compute ERD (percent change) ? 

3-Is it possible to use the statcond() function to do this kind of statistical analysis : Compare ERSP between 2 differents conditions of multiple subjects for each channel ? What is the format of data given in the workspace ?

4 - Is it ok to do a wavelet transform [7 0.1] for frequencies between [7-23] ? Because I lost the first second (-4000 to -3000ms) doing this kind of wavelet transform.

Sorry for all these questions at the same time but if anyone could give me some leads I would really appreciate because I don’t know if i’m doing right …

Sincerely,

Benjamin, 

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