This section covers everything from experimental design through MEG data analysis, but since analysis is usually the most time consuming part of a study, and since the type of analysis you want to do will guide your design, it's really all about the analysis.
A new feature with the 5.2 tools is CHL. Head position is recorded continuously throughout a run. Special channels in the dataset store the (x, y, z) coordinates of the head coils. Since this is a major interface change in acquisition, it warrants a special mention here.
To use it, select "continuous" in the Channel Settings window. There will only be one "localizer window" at the beginning, so you may want to modify your Presentation scripts to reflect that.
After a recording, the "Run Status" window pops up. We usually click OK on that, but now that window contains the final Max Head movement number. So instead of the post-run localization movement number you can use that. Note: it's not the difference between pre and post, it's the max movement, no matter where that occurred. If you click OK on Run Status by accident, the same number is still available in the lower left of the
Acq window (that we normally dismiss with File→Close Window).
Furthermore, there is a new program,
headMotionDetect, which will scan a dataset and identify (and optionally mark as bad) segments with motion exceeding a threshold.
headMotionDetect -th .25 dataset.ds
will identify segments by trial and time with motion exceeding 2.5 mm, and in this case it doesn't create any markers, it just reports. The default threshold is 5 mm.
newDs will now always report the max head movement when it creates a new dataset.
If you're looking for MEG analysis software, that's here.
MEG datasets are large, complex, and rich with information. There are many ways to look at them. Here I'll briefly outline the basics.
Averaging. Spectral analysis (
ctf2st). Artifact rejection. Dipole fitting.
A common processing flow for group analysis is as follows:
SAMsrc step depends on a head model, usually derived from the subject's structural MRI scan.
The steps above are covered in more detail here, and the Software page has lots of tools you'll need.
See a list of all the pages in the Meg group.
This section details known bugs in the CTF MEG software.
The last version. The "new" feature in this release is brain shapes instead of head shapes. It has oddities that will never be investigated. Don't use it, stick with 5.2.
localSpherescan sometimes produce garbage results. Use
checkSpheresto check, or just look at the
MultiSpherefile and make sure it doesn't have ridiculous values in it. Fixed in 5.0.1.
This is a list of things that we'd like to have.
fiddist, and report on the amount of mismatch between the MRI and the MEG fiducials.