[Eeglablist] interpretation of weights on scalp maps

Jed Meltzer jedmeltzer at yahoo.com
Thu Feb 27 14:13:51 PST 2003

I have a conceptual question about the weights in an
ICA decomposition.  As far as I understand it, each
point in time on each channel is multiplied by the
inverse weight and sphere matrices to output each
point in time in the component activations.  Some of
these weights are negative.  Does this mean that a
positive deflection in the component corresponds to a
negative deflection in the channel?

The reason I ask is because I don't know how to
interpret the scalp maps of components.  Are red parts
and blue parts equally important?  That is, do they
both represent that the component maps strongly onto
the channels in the colored region?  That would mean
that the green regions are the ones that are not
affected strongly by the component.  Furthermore, one
could then infer that if a red region and a blue
region are close together, then the underlying source
may be modelled by a single dipole located in between
the two colors.  

Or am I understanding this incorrectly?  Does blue
mean minimal projection?  

-Jed Meltzer
Yale University

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