Problems with second level source statistics for multi plew subjects and firsty level stats - solved :-)

[Michael Wibral]

Dear listusers,

in several previous mails I have reported about problems occuring when:

1) doing single subjects source analysis using reverse-normalized grids (thanks to Ingrid's tutorial), common filters for the two conditions and generating single trial source data
2) then performing single subject sourcestatistics (getting a sparse data representation with a stat field)
3) then doing second level sourcestatistics (which didn't work)

I am happy to report these problems are solved :-). I actually just overlooked a WARNING:... when doing single subject sourceanalysis and sourcestatistics (1st level) is says that you yourself have to add a dim field by hand, when trying to use clusterrandanalysis/sourcestatistics later. I now simply added a dim field to both, to the data and to the cfg for the second level source statistics. The correct choice for this dim field are the dimension of the original, orthogonal, regular grid in MNI space and everything works now.

 I just didn't realize that dim can't be all that easily generated automatically by fieldtrip for sparse data and *warped* grids. This is because the warping could - in principle - be such that dim doesn't make any sense anymore, e.g. because points (almost) switch places along a certain dimension (if they differ in the other coordinates). So neighborhood relations are not well defined a priori in sparse data. Hence, the need for a manual addition of dim in this case (please correct me me if any of the above is wrong).

The version I used and that I can confirm to work was 20081208.

Many thanks for all your support,
Michael



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