[Eeglablist] EMG artifact question

[Bachman, Peter]

Hi everyone,
 
In the course of using ICA in EEGLAB to remove artifacts from EEG data, I've noticed that what appears to be EMG-related contamination will sometimes not only persist in the dataset, but actually appear to become somewhat amplified and even distributed over channels in which it did not appear in the raw data.  
 
I can imagine why EMG activity may be less likely to collect on to a single component for easy removal - so why it would not be easily removed - but I'm not sure why it would appear to be more of a problem after the raw data is decomposed with ICA and then reconstructed back into EEG channel data (with amplitude scale and other parameters held constant).  
 
I've attached two .gif images with examples of this phenomenon.  In both instances, eye blinks are removed very nicely, but EMG activity seems worse after the cleaning.  
 
I'm wondering if anyone else has seen this before.  If so, do you understand why this might happen and how to avoid it?
 
Thank you very much!
Peter
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