[Eeglablist] Subtracting conditions

[Kaelasha Tyler]

Hi all,

Will the following work to subtract the eeg/ERP in one condition
(ALLEEG(1)), from the eeg/ERP in another (ALLEEG(2)):

ALLEEG(3)=ALLEEG(2)

ALLEEG(3).data=ALLEEG(2).data-ALLEEG(1).data

eeglab redraw

In this case, I have two data sets loaded into EEGlab: ALLEEG(1) and
ALLEEG(2).
These are the eeg trials in the two different conditions, both are aligned
to the same specific time point and contain an identical number of
trials, data points etc.
I created ALLEEG(3) as a replica of ALLEEG(2) in order to house the new
data.
Then I replace ALLEEG(3).data with the data created by subtracting the two
conditions.
ALLEEG(3) is what I hope the ERP subtracted data to be. Eg, when I plot
channel ERPs for ALLEEG(3) I hope these will be the resulting event related
potentials of one condition subtracted from the other.
If needed, I will run an ICA on ALLEEG(3) afterwards, to create new
components based on the subtracted data.

WIll this work? Are there any problems with subtracting data this way?

I see some previous email threads regarding subtracting conditions, using
ERPlab and command window scripting using the Study structure.
However I would like to keep it simple and use a small script without
resorting to creating a study structure or using ERPlab.

Thanks in advance,
Kaelasha