ICA based artifact correction and phase-locking

Markus Werkle-Bergner werkle at MPIB-BERLIN.MPG.DE
Fri Feb 23 12:24:42 CET 2007

Dear all,

in my studies, I'm investigating early preceptual binding (visual)
across the lifespan (i.e., I have data form children, younger and older
adults) with EEG measures. My main interest concerns changes in
gamma-power and measures of phase-synchronization in the gamma frequency
range(e.g., phase-locking index, n:m (theta:gamma) phase synchronization).

Currently  I use a 'semi-automatic' procedure for artifact rejection,
i.e., I use thresholding in the time-domain (min/max in segment -/+
100┬ÁV)to 'suggest' contaminated epochs. After that I visually inspect
the data again for eye-blink and muscle activity, and completely reject
the contaminated epochs.

The problem with this procedure is that, especially in the older adults
group, for many subjects only too few trials remain in the final sample.

Therefore, I thought I could use ICA for artifact correction (instead of
complete rejection). After identification of the components that reflect
muscle activity (and also other artifacts), I thought to recombine the
remaining ICs and perform my analyses (power, PLI, n:m synchronization)
on the recombined (cleaned data).

Now my question(s): Is there any experience whether removing certain ICs
may change the phase spectrum, i.e. may this approach induce some
systematic bias? If there is a systematic bias, are different frequency
bands affected differentialy? Could anyone give me some references on
these issues?

Any comments are very much appreciated.

Best regards,

Markus Werkle-Bergner, Dipl. Psych.
Predoctoral Research Fellow

Center for Lifespan Psychology
Max Planck Institute for Human Development
Lentzeallee 94, Room 211, D-14195 Berlin, Germany.
Phone: +49(0)30-82406-447       Fax: +49(0)30-8249939

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