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Begin forwarded message: > From: Gustavo Sudre <[log in to unmask]> > Date: February 27, 2009 9:57:18 AM EST > To: [log in to unmask] > Subject: discontinuity in raw data > > Hello, > > For many repetitions in my experiments I have observed a > discontinuity in the raw MEG data. This happens in some of my > individual trials, and it is not always across several channels > simultaneously. The attached picture shows an example of this type > of noise, for a particular trial and channel. When I notice such > pattern during recordings, reheating the sensor usually works. > However, I don't catch them all the time, so it's often the case > that I see this pattern in recorded data. These are my questions: > > 1) What causes this noise? Can the channel be "trusted" even if it > shows the pattern a few times? > > 2) If I run my data through SSS, this pattern seems to appear in > many more channels. That means that I need to discard many more > repetitions after running SSS. Is this something intrinsic to the > SSS algorithm (i.e. to multiply this noise)? What is the reason for > it to appear across more channels after SSS? > > 3) If I clean up my raw data prior to SSS (e.g. discard the > repetitions with such pattern), and create a new FIF raw file from > this new data, my data won't be continuous in time anymore. I don't > think SSS will have a problem with it (unless I use the temporal > extension). Is that correct? > > 4) Would you suggest a more accurate way to deal with these > discontinuities (eg. wavelets?), instead of discarding (sometimes > precious) trials? > > 5) Assuming SSS has no problems with this new "clean" raw file, can > the SSS algorithm create such discontinuities by itself? If so, why? > > Thanks, > > Gus >