[Eeglablist] how to select channels for back-projection of ERP

[Elizabeth Milne]

Dear EEGLAB team,
I have a question about resolving the "true" polarity of IC ERPs by
back-projecting to channel data. Using erpimage, I have obtained the ERP of
an IC, but the polarity is different (orthogonal) when back-projecting to
different channels. In another example from a different IC, the polarity of
the ERP does not change, but the amplitude of the signal is different
depending on which channel is selected for back-projection.

If I want to use this, or any other, IC to measure the amplitude / latency
of particular ERP deflections it is necessary to know which is the correct
channel to choose for back-projection. However, I am unsure as to how to
make this decision objectively. Are there particular features that I should
look at to make this decision more systematic, i.e. dipole projection? %
power accounted for?

If anyone can offer advice, or point out errors in my understanding I'd be
very grateful.

Many thanks,
Elizabeth

-- 
Elizabeth Milne
Reader in Cognitive Neuroscience
University of Sheffield
Western Bank
Sheffield
S10 2TN

+44 (0) 114 222 6558

http://www.autismresearchlab.group.shef.ac.uk/
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