arno at salk.edu
Tue Feb 15 11:34:56 PST 2005
your comments are correct.
>My concern is that for a given participant, there may be less artefact-
>free trials in Block 1 than Block 2 and this should be weighted
>accordingly so that Block 2 contributes more to the individual average.
>The grand average I would imagine to be a straightforward average of all
>the individual averages in the group and should be not weighted.
The pop_comperp() function considers that you want to compute a grand
average ERP across several subjects, not across two trial averages of
the same subject. One of the reasons is that, in EEGLAB, we consider
that all blocks of each subject should be concatenated (for running ICA
for instance; note that you should not do that of course if a subject
EEG has been recorded on 2 separate days). If you want to apply standard
t-statistics across subjects, you cannot weights the trials average of
each subject by the number of trials in each sub-average. Also, you do
not want one subject with more trials to dominate the average. I
acknowledge that ERP tools in EEGLAB are not optimal and that we should
introduce the option you mentioned. Any other comments or suggestions
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