[Eeglablist] negative power values in spectrum

[Christian Scharinger]

Dear eeglab users,

I'm still struggling with the question why eeglab calculates spectra 
with negative power values for my data in a study design.
Reading the eeglab documentation and surfing through the eeglablist 
archives I didn't find a solution how one could get spectra with 
absolute power values in eeglab study design.

When I use fieldtrip instead of eeglab for calculating spectra I get the 
data I'd like to have (that is positive absolute power values). But I 
really like the opportunities eeglab offers in study design, so I'd like 
to stay within this framework if possible.

Maybe someone has any suggestions for my problem (see code below)?

I'm sorry to bother the list again with the same question, but as I got 
always very helpful comments from the list for other questions I had in 
the past (many thanks!), I'd be glad about any helpful comments this time.

Best
Christian



I use the following code for calculating the spectrum in a STUDY design:

[STUDY ALLEEG] = std_precomp(STUDY, ALLEEG, 'channels', 'design', [1], 
'erp', 'off', 'spec', 'on', 'ersp', 'off', 'specparams', { 'specmode', 
'psd', 'recompute', 'on', 'timerange', [1300 1800], 'freqfac', [4] }, 
'savetrials', 'off');

STUDY = pop_specparams(STUDY, 'groupstats','on', 'mcorrect','fdr', 
'threshold',0.05,'plotgroups','together','freqrange',[1 30], 
'rmsubjmean', 'off');

With this code, I'm getting negative power values...

So I guess I'm not getting absolute power values (what I would like to 
have) but power values in relation to some kind of baseline.

Is it possible to get absolute power values for a spectrum in a STUDY 
design?
Where can I see/change what baseline eeglab uses for calculating power 
values?

Many thanks in advance,

Christian