[Eeglablist] same IC for different ERP components?

[Baris Demiral]

Dear all,

My question is related to the Independent Component - ERP component mapping.
A bit theoretical. I will make a distinction between IC; independent
component, and ERPC; ERP component.

I conducted ICA (runica-extended) by feeding the four conditions of my
experiment (2x2; stimulus type x stimulus features).
I then separated two factors (stimulus types) from each other, and built two
study files for each factor to compare the levels (features) in ERP and IC
domains.

Then I did pre-clustering with PCA reduction to 10, then hierarchical
clustering for the ICs in each study file separately, defining 3 final
clusters.

Interesting thing was that one of the IC clusters' scalp map of study1 was
almost identical to one of the IC clusters' scalp map of the study2, BUT in
ERP waveforms these two ICs were showing two distinct "ERP components" (as
eye balled over the ERP difference between the conditions, one condition
differing from the other as in classical ERP component selection etc..) I
was expecting that the IC clusters with the same scalp topography should map
to the similar ERP waveforms (components) for both factors.

Is this possible? Can I conclude that the same IC and maybe the same
cortical area generate two different ERP components depending on the
condition?

-- 
SB Demiral, PhD.
Department of Psychology
7 George Square
The University of Edinburgh
Edinburgh, EH8 9JZ
UK
Phone: +44 (0131) 6503063
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