[Eeglablist] A quick question about baseline correction after ICA

[Scott Makeig]

Zhu -

David Groppe pointed out that running ICA after baseline-correcting
individual data epochs essentially adds a new (baseline mean) map to each
trial, one that depends on the length of the epoch as well as on the
underlying data sources. He found that he got better ICA decompositions when
he (1) applied high-pass filtering (as however appropriate) to the
continuous data, (2) extracted event-related epochs of interest, (3)
performed ICA decomposition on the concatenated epochs, and then (4) applied
baseline correction to the epochs. This seems theoretically sound -- I
suggest trying this approach.

Scott Makeig

ps. Below you don't say exactly what you mean by A and B ...


On Tue, Dec 22, 2009 at 1:59 AM, zhu zhu <zhuzude at gmail.com> wrote:

> Dear All,
> I have a puzzle when extract epochs from ICA-back projected data. Let' say,
> I selected one component after ICA, when I extract epochs for a specified
> marker (condition), should I use baseline correction (default = -200 0)? The
> reason I ask this question is that I the data was baseline corrected before
> ICA, and sometimes the baseline correction during extracting epochs will
> change the relative amplidute( i.e. A > B without baseline correction, but A
> < B after using baseline correction). Any comment is highly appreciated!
> Thank you!
> Best regards,
> Zude
>
>
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-- 
Scott Makeig, Research Scientist and Director, Swartz Center for
Computational Neuroscience, Institute for Neural Computation, University of
California San Diego, La Jolla CA 92093-0961, http://sccn.ucsd.edu/~scott
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