 |
 |
I think you need to check the actual magnitude of position transformation
(distance by which the head was ‘moved’) in the MF log. The larger the
distance, the more it amplifies noise (and if the head was not close to the
sensors in the first place, there is not much signal to amplify). Our internal
discussion here was that moves of more than ~2 cm are too large to produce
decent data.
-yury-
From:
Announcement for the Neuro MEG list [mailto:[log in to unmask]] On
Behalf Of David Ziegler
Sent: Thursday, October 28, 2010 3:26 PM
To: [log in to unmask]
Subject: problem with maxfilter
Hello
Neuromeg users,
I am having a problem running maxfilter 2.0 on my MEG data to auto-detect bad
channels and transform each subject's head position. In about half of the
cases, the results look good, but occasionally the resulting data seem to be
noisier than the original data. I am aware of the known bug where using
"-trans default" w/o specifying -frame and -origin results in noise
at the vertex. This is exactly what I am seeing, but I did specify these
two parameters in my command.
I am attaching two figures, one with maxfiltering and one w/o (the data have
been read into fieldtrip and I am displaying only the gradiometer data.
also, the channels are plotted numerically, but the sensors with the noise tend
to be close to the vertex). Does anyone have an idea as to what might be
going on and what I can do to remedy the problem?
The command I ran is:
maxfilter -f $f_i{each subjects fif file} -origin 0 0 40 -frame head -autobad
30 -badlimit 7 -in 8 -out 3 -trans default
Thanks!
David
--
David
A. Ziegler
Department
of Brain and Cognitive Sciences
Massachusetts Institute of Technology
43 Vassar St, 46-5121
Cambridge, MA 02139
Tel:
617-258-0765
Fax:
617-253-1504