[Eeglablist] Computing a second ICA on a dataset

[Jan R. Wessel]

Hey everybody,

I'm analyzing an EEG dataset on an eye-movement task. In order to cope 
with the massive eye-movement artifacts, I computed a normal ICA on the 
dataset and got rid of all the oviously eye-movement related components. 
Now, I'm trying to compute a second ICA in order to clean up the data 
even more, because there is still considerable saccadic activity in most 
of the datasets.

When I'm doing this, I'm running into a series of problems. Seemingly 
depending on the memory of the machine I am running it on, a) either the 
ICA takes days to compute for a single subject, b) or Matlab terminates 
without any prompt, leaving me with a "segmentation fault" in the unix 
terminal or c) if it runs until the end, it seems to give me (and here 
comes the really weird part) complex numbers (!) such as 
"0.009259085778863 + 0.013638045843933i" as ICA weights. When I display 
the component activations, I get some funny activation spots in the 
bottom left corner of the plot, while the rest of the plot is blank. 
This effect is regardless of which epochs I display.

So obviously, the second ICA doesn't really seem to work out. Does 
anybody have any experience with consecutive ICA analyses or has even 
come across the same problem and can maybe help me out here?

Thanks in advance,
best,
Jan

-- 
Jan R. Wessel, Dipl.-Psych.
Cognitive Neurology Research Group
Max Planck Institute for Neurological Research
Gleueler Straße 50
D-50931 Cologne
Phone: 0221 - 4726 343
Mail:  Wessel at nf.mpg.de