# [Eeglablist] When ERSP Baseline is not specified

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Fri Sep 4 11:32:11 PDT 2015

```Dear James,

This is from newtimef() line 945. Probably not exactly the same thing you
run, but the basic idea of 'commonbase' can be seen. Looks like it's an
average of two (or more) baselines.

Makoto

% recompute power baselines
% -------------------------
if ~isnan( g.baseline(1) ) && ~isnan( mbase1(1) ) &&
isnan(g.powbase(1)) && strcmpi(g.commonbase, 'on')
disp('Recomputing baseline power: using the grand mean of both
conditions ...');
mbase = (mbase1 + mbase2)/2;
P1 = P1 + repmat(mbase1(1:size(P1,1))',[1 size(P1,2)]);
P2 = P2 + repmat(mbase2(1:size(P1,1))',[1 size(P1,2)]);
P1 = P1 - repmat(mbase (1:size(P1,1))',[1 size(P1,2)]);
P2 = P2 - repmat(mbase (1:size(P1,1))',[1 size(P1,2)]);
if ~isnan(g.alpha)
Pboot1 = Pboot1 + repmat(mbase1(1:size(Pboot1,1))',[1
size(Pboot1,2) size(Pboot1,3)]);
Pboot2 = Pboot2 + repmat(mbase2(1:size(Pboot1,1))',[1
size(Pboot1,2) size(Pboot1,3)]);
Pboot1 = Pboot1 - repmat(mbase (1:size(Pboot1,1))',[1
size(Pboot1,2) size(Pboot1,3)]);
Pboot2 = Pboot2 - repmat(mbase (1:size(Pboot1,1))',[1
size(Pboot1,2) size(Pboot1,3)]);
end;
verboseprintf(g.verbose, '\nSubtracting the common power baseline
...\n');
meanmbase = mbase;
mbase = { mbase mbase };

On Wed, Sep 2, 2015 at 11:27 AM, James Jones-Rounds <jj324 at cornell.edu>
wrote:

> Hello all,
>
> We're trying to interpret some STUDY ERSP results. Specifically, one
> question we have is what time window the "Compute common baseline" uses to
> compute a baseline, in the GUI pop-up for selecting ERSP Parameters, in the
> "Edit/Plot Clusters" STUDY menu option.
>
> I've found (http://sccn.ucsd.edu/pipermail/eeglablist/2013/006558.html )
> seems to suggest that you can only specify an ERSP baseline if you use the
> command-line version of the functions, and also that's only for the
> pre-computing step.
>
>
> James
>
> --
> James Jones-Rounds
> Laboratory Manager
> Human Development EEG and Psychophysiology (HEP) Laboratory,
> Department of Human Development,
> --------------------------------------------
> Cornell University | Ithaca, NY
> 607-255-9883
> eeg at cornell.edu
>
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--
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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