[FieldTrip] follow-up on grad fields with NaNs after ICA

[Vitória Magalhães Piai]

Hi FT-ers,

It took me a while to find some older posts that would answer my 
question, and this thread almost did the whole job:
http://mailman.science.ru.nl/pipermail/fieldtrip/2013-July/006779.html
http://mailman.science.ru.nl/pipermail/fieldtrip/2013-July/006788.html

Like Alex, I figured out that it was the ICA that left my grad.chanpos 
with NaNs only, and like Haiteng, I thought just replacing the grad 
field with a pre-ICA grad field would be one way to go.
But just like Alex I was wondering whether this is the right way to go: 
"however, it feels somewhat dangerous to perform such "dirty" fixes, 
since that grad info is probably removed for a certain reason. We are 
oblivious to its impact subsequent steps like planar transform and 
source reconstruction."
Talking to a knowledgeable colleague yesterday about this issue, he also 
had his question marks. But I don't see any follow-up on Alex's remark 
(I guess he further discussed this with colleagues while drinking coffee 
at the DCCN kitchen...! :-)
SS
So I still don't know the answer and maybe some other people may want to 
know it as well in the future.

Any opinion on whether it's safe to use pre-ICA grad information for 
subsequent planar transformation and source analyses?
Thanks a lot, Vitória

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