[Eeglablist] filtering and ica

[Natasa Kovacevic]

Here, at Rorman Research Institute, we acquire Neuroscan eeg data which
always has 60Hz line noise. For the types of time-frequency analysis
that we want to perform, we need to filter this noise out. When we apply
ica decomposition for artifact removal it is quite clear that many ica
components pick this noise up to various degrees. So the question is:

should we first filter this particular noise and then run ica, and if
so, would notch filtering at 60 Hz of the raw, continuous data be the
best (as opposed to say filtering epoched, manually pruned data)?

or would it be better to 

run ica, remove artifact-related components (some of which will usually
contain some of the 60Hz noise) and then filter the clean data?

Also, why is it recommended to run ica on shorter epochs and then apply
weights to longer epochs - is it simply to reduce computation time?
Because, it seems that with such approach artifacts that may be present
in longer epochs only (e.g. eye blinks) will not be removed.


Many thanks,

Natasa Kovacevic, PhD
Rotman Research Institute
Baycrest Centre for Geriatric Care
Toronto