[Mne_analysis] Grand Averaging from Text Events Files

[Brian Coffman]

Hello MNE users,
I am having an odd issue that I am having trouble conceptualizing.

I am averaging data that is split into 3 raw data files, then taking the
events files generated from these averages and modifying these events files
to include only events where the subject responded correctly. I am then
taking these corrected events files and grand averaging the raw data to end
up with a single .fif average which is corrected for our behavioral data.

The issue I am having is related ot the initial offsets in the events
files. In all cases, there is an initial offset greater than zero for the
2nd and 3rd raw data files. In some cases, there is also an initial offset
of a few seconds in the events file for the first of the three raw data
files. It seems from the log files that the offset is being utilized
differently for the two cases (a few seconds offset vs a whole dataset
offset). For the log from the first file, the offset is added to the times,
while for the other files, the offset is not added. For example, with an
initial offset of 4 seconds, the log for the uncorrected average starts at
29.555 seconds, while for the corrected data, the log starts at 33.555
seconds. The logs are identical for the second and third data files. This
is also apparent in the averages, as there is no signal in the corrected
average of the first raw file. It seems that the offsets are necessary for
the later files (data files 2 and 3), however, as I get no averages without
them.

My question is: Should I eliminate these offsets from the first text events
file when averaging from events files? Is there something I have not
considered here?


Thanks in advance!!

-Brian Coffman, M.S.
Research Associate, The Mind Research Network
Doctoral Candidate, The University of New Mexico

Phone: (505) 336-0606
Fax: (505) 272-7011

"I used to think that the brain was the most wonderful organ in my body.
Then I realized who was telling me this."
  - Emo Phillips
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