[Eeglablist] removal of event-related (time/phase-locked) variance
from ongoing oscillatory activity (cf. Makeig '93)
smakeig at ucsd.edu
Mon Dec 19 16:05:33 PST 2005
Re the model: EEG = evoked + induced as raised in recent posts.
Although this model is easily stated, it is not necessarily
representative of the actual generation of event-related EEG dynamics
See our recent TICS paper via http://sccn.ucsd.edu/papers/TICS04.html
for a discussion of a more flexible modeling environment in which ERP
phase-locking and power spectral changes (or perturbations) are axes of
an event-related state space in which all phenomena (at the cortical
level) occupty some region -- but rarely live at the 'pure ERP' / 'pure
One place in EEGLAB where we use the model above is in computing
event-realted component (or channel) cross-coherence using crossf().
There we have an option to remove the ERP from each trial -- this
removes the possibility that observed coherence arises through common
ERP features for the two processes being compared. This is a highly
conservative approach -- since in fact whatever causes the common ERP
might also cause a change (usually, increase) in coherence.
This issue is far from settled settled - I believe it will require
modeling the trial-to-trial variations in ERP/EEG to more adequately
address the degree of meaning in the model above in particular cases...
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