[Eeglablist] importing ERPs

[Arnaud Delorme]

Dear Josh,

If you provide a simple data average to EEGLAB, it thinks that this is continuous data. EEGLAB expects data epochs. You may trick EEGLAB by duplicating your data epochs and then all of EEGLAB ERP functions should work properly.

EEG.data(:,:,3) = EEG.data;
EEG.trials = 2;
EEG = eeg_checkset(EEG);
eeglab redraw;

You may plot differential ERPs using menu item "Plot > Sum/compare ERPs".

Best,

Arno

On Sep 4, 2012, at 2:23 PM, Stephen Politzer-Ahles wrote:

> Hi Josh,
> 
> While there's no way to do difference topoplots from the user interface (as far as I know), the input to topoplot() is just a vector of amplitudes (1 measurement for each channel), and thus it can be done straightforwardly from the command line. If you have your two conditions (could be single-subject or grand average data), and put the data from each one into a variable, like
> 
> condition1 = EEG.data;
> ...
> condition2 = EEG.data;
> 
> Then you can subtract them:
> 
> diff = condition1-condition2;
> 
> And get a mean over some particular time window:
> 
> mean_to_plot = mean(diff(:,starttime:endtime),2);
> 
> Then you can feed "mean_to_plot" to topoplot(), along with whatever other parameters you want.
> 
> The details will of course vary depending on the format of your data, how you have grand averages saved or not, etc. But I can send you a sample of the code I used for my data if you like.
> 
> Best,
> Steve Politzer-Ahles
> 
> On Mon, Sep 3, 2012 at 10:17 PM, Joshua Hartshorne <jkhartshorne at gmail.com> wrote:
> I have been trying to plot difference waves (well, really difference topoplots) in EEGLab. Since there didn't appear to be any way to actually do this, I thought I'd get around the problem by exporting the data, computing the condition averages, subtracting the one condition from the other, and then reimport in order to then plot.
> 
> Unfortunately, importing has not bee working. I followed several examples in the wiki, including the one for Matlab arrays which gives and example involving made-up data (http://sccn.ucsd.edu/wiki/A01:_Importing_Continuous_and_Epoched_Data#Importing_a_Matlab_array) but invariably get the following error:
> 
> eeg_checkset warning: 3rd dimension size of data (1) does not match the number of epochs (0), corrected
> eeg_checkset warning: number of columns in data (25600) does not match the number of points (0): corrected
> eeg_checkset note: upper time limit (xmax) adjusted so (xmax-xmin)*srate+1 = number of frames
> 
> When I plot the data, it ignores anything I told it about where the epoch starts (e.g., -0.2) and starts the epoch at 0 regardless. And when I edit channel info, it says there is only 1 channel, even though it's happy to plot all the channels. 
> 
> Does anybody have any idea what might be happening?
> 
> Josh Hartshorne
> 
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> 
> 
> -- 
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://www.linguistics.ku.edu/
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