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

Elizabeth Milne e.milne at sheffield.ac.uk
Fri Jul 31 14:13:50 PDT 2015

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

+44 (0) 114 222 6558

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