[Eeglablist] single trial phase locking

[Michiel Spape]

Dear fellow EEGLab users,
Having used EEGLab for a while now to compute inter-channel (phase, etc) coherence, I recently stumbled upon the following article: http://brainimaging.waisman.wisc.edu/~lutz/Lachaux_et_all_IJBChaos_2000.pdf ("studying single-trials of phase synchronous activity in the brain", Lachaux et al., International Journal of Bifurcation and Chaos (!), vol. 10, 2000) where the authors are describing a method for studying phase locking in single trials. As far as I understand, if we do such a thing in EEGLab, we would just get a coherence value of 1, by definition. So, I was wondering whether someone could help me along the way of getting this to run in EEGLab, (I'm okay with matlab scripts, just not with hardcore math).

Recently, although I cannot find the specific email anymore, someone else had a similar enquiry. Something quite possible, even easy, to do in EEGLab would be to hack an epoch to 'sub-epoch' pieces - say, turn my single 5 second epoch into 200 overlapping ones, with each being 200 ms (so they'd overlap quite a lot), run newcrossf over that, et voila. Yet, this does not seem like the ultimate answer, since it is, quite possible that channels should first synchronise for a few hundred milliseconds at one angle, then 'scatter', and a few hundred milliseconds later, resynchronise over another, possibly even opposite angle.  It seems to me like Lachaux et al. here suggest something to cope with it - that is, we could use, for instance, 4 wavelet cycles across time to extract angles, and then use an 'integration window' of 8 cycles (see figure p.2432) to compare 8 angles and see whether they point in the same direction.

So, my proposed way of doing this in EEGLab would be to, for example, re-epoch my 5 seconds in 5 consecutive 1 second epochs, then hack each 1 second epoch in 8 200 ms epochs (a bit overlapping), and thus compute, 5 times, the ITC over this. Does this sound sane to you?

Best,
Mich

Michiel Spapé
Research Fellow
Perception & Action group
University of Nottingham
School of Psychology
www.cognitology.eu

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