Dear Brainstorm community,
I was hoping to calculate source differences for some ERPs in a pre-post (within subject) design, in which each test session had two conditions I would like to compare is a pre-post fashion.
After trying my best to follow the tutorials, workflow, and some guidance from previous posts here on the discussion forum (e.g. Statistics on sources), here is my general pipeline that I ended up going with:
- used the default anatomy for each subject
- EEG data was already preprocessed prior, so I simply imported the .set files for each subject, separating each file to its appropriate condition
- created an average for each condition within each subject
- generated BEM surfaces with adaptive integration
- calculated the noise covariance matrix using the individual trial file for each subject using the pre-stimulus period of the condition with the most trials (this may be wrong, but I don't think it would explain the errors I eventually run into)
- I then estimated the sources with the unconstrained option
- With these sources, I then applied the baseline correction of Z-score wrt baseline
- I then applied the Flatten process (process: Sources > Unconstrained to flat map) due to having used the unconstrained option prior
At this point, I add each the '...| zscore | norm' files to process 2, the pre files to A and the post files for B, trying to compare one condition in a pre-post fashion. I then select 'parametric test:paired', limit my time window to 200 - 300 ms while leaving the rest of the options as their default, and run.
Here, I get a resulting 'stat' file titled 't-test paired', but after clicking it to see the results, I see a flat-line in regards to t-test values, and have the warning pop up: 'Warning: Cannot determine t-test side'. When running different types of analyses, I also run into 'All Values are null. Please check your input file'.
A couple of questions: a) is my pipeline correct in the sense that I should be able to do source statistics on it and b) what am I doing wrong to both receive this warning and see a flat-line of zeros/all values being null.
EDIT - just saw this post by Francois (P value of ERD analysis), is it fair to assume that my second question is simply due to a lack of significant results or is there something wrong with my preprocessing?
Any help would be greatly appreciated.