Hello everyone,
I have a question about the 'old' versus 'new' event (.eve) file formats
and how those are treated by the mne_process_raw function during
epoching.
In one of my single-trial analyses I had to replace trigger values in
the raw event files with custom values. I ran those and all seemed well.
Now I am re-using the same .eve files again and noticed when they are
read with the mne_process_raw I get a warning that these event files are
detected as 'old format'. This is happening because when replacing the
triggers I also replaced the trigger value in first line of the event
file (which is meant to be 0) to some non-sense value (7777 - as for all
events of no interest). The first line of the event file encodes the
first pseudo event and the timing in this line and the sample number are
critical so if I replace these, all subsequent epochs will be
misaligned. But I didn't change these - just the value of the digital
trigger channel (i.e. ,the <to> value).
MNE manual (I am using 2.7.3 version), however, warns not to touch this
first line at all. As this line helps the software to interpret the file
format ('old' vs 'new'). But I can't find anywhere what this actually
means and how would the epochs be treated in the old format? I only know
that in the old format .eve file did't have this first empty event. But
new mne is backward compatible and deals with this somehow.
So I ran with both 'old' (with 7777 non-sense trigger in the 1st line)
and 'new' (the same but with correct 0 trigger value) event files,
looked at the single trial epochs and they are identical (I get a matrix
of 0s when i subtract one from the other). So the question is - does the
trigger value of the first line matter then? Or would both 'old' and
'new' versions of the event file be treated in the same way - i.e the
value of the first sample in the first line be subtracted from the
subsequent epochs?
Thanks,
Ana