[Eeglablist] bad channels removal before ICA

[Jia Wu]

Hi Everyone,
I have a very basic question towards the processing
ICA-artcifact-removal. We use a 128 channels systom to get ERP.
Sometimes we have bad channels because of the high impedences in them.
What should I do in the two cases below?

1, I do ICA on averaged data. The averaging program can detact and
remove bad channels. I have two questions here. 1.1, after averaging,
the bad channels are replaces by 0 if they are bad most of the time.
What should I put in ICA? I don't think I should put 0 in it. So should
I use the averaged data from adjacent channels? 1.2, The averaging
program seems to be able to detact and remove eye blinks data also. Then
what the meaning of doing an ICA on the data?

2. I do ICA on single trials. Should I just remove the bad channels by
visual examination? If so, the same question as above, after i remove
the bad channels, what data in the bad channels should I use in ICA,
averages of adjacent channels?

Finally, I actually don't know whether I need to do anything on the bad
channels before ICA. I guessed ICA could separate the bad channels out
by different components. But it is not proved by my work. When I put
data including some bad channels in ICA, I tried to get 128 components.
At least the first 10 components (having the largest variance) only
represent the bad channels. I don't think it's right to remove the 10
largest components in ICA, is it?

By the way, should ICA be applied on averaged data or single trial? If
on single trial, I still need to average it in the later ANOVA. So
what's the difference?

I'm eagerly waiting for anybody's hints.

Thanks,
Jia