[Eeglablist] Line noise

[Christina Karns]

I'd like to hear some opinions about the best way to deal with line noise.
I have a relatively clean dataset where the power spectrum of the
continuous data shows relatively little 60Hz line noise (we use the
Biosemi system which is less susceptible to line noise than some other
systems). Should I use a notch filter or ICA to separate out any line
noise contributions to the data?

1. One approach would be to use ICA to separate out the line noise.
According the the EEGLAB manual, "ICA can separate out certain types of
artifacts -- only those associated with fixed scalp-amp projections. These
include eye movements and eye blinks, temporal muscle activity and line
noise." Note that, "when a source distribution is sub-Gaussian (e.g., as
with line noise), the extended power spectrum and three event-related
time/frequency option of infomax ICA must be used to separate it."

2. However a previous discussion on this list:  (see
http://sccn.ucsd.edu/pipermail/eeglablist/2004/000716.html) suggests that
it would be better to notch filter the data and then perform ICA so "any
artifact of independent origin is likely to occupy one degree of freedom
in ICA space to model that artifact. If you have too many, you are likely
to be left with no degrees of freedom for sources of interest."

It seems that the advantage of using ICA to separate out the line noise is
that there may be neural processes that overlap with the 60Hz frequency
band that would be filtered out with the notch filter. In constrast, ICA
should be able to distinguish these if they are independent.

Do you have any advice for me?

Thanks,

**********************************
Christina M. Karns
University of California, Berkeley
***********************************