Dear Vladimir and SPMers,
Thank you for your reponse to my data converting problem.
I have an another question about SPM MEEG,
scaling of the evoked/induced power image in spm_eeg_inv_Mesh2Voxels.
Why does SPM conduct the global scaling of the power image?
For exmaple, in PET-CBF measurements,
scaling is important to evaluate the local neuronal activities
because the local signal changes covaried with the global signal changes.
For fMRI with global signal fluctuations, we often choose scaling option
to increase sensitivity for signal detection.
Are these true of MEEG power data?
Or is there another rationale for scaling?
I have learned the importance of scaling over some test analyses,
however, I would like to confirm a theoretical rationale.
The following are my test analyses:
I performed the source localization on multi-subject MEG data
with 2 task and 2 control conditions.
Smoothed power images were written out for each condition and
they were entered into the second level repeated measures ANOVA.
Contrast of task vs. control was evaluated.
(The issue of non-normality put aside so far.)
Results were varied among 3 different scaling methods,
scaling none, by whole conditions used in r3408, and by each condition used in r3684.
Localization was best for r3684 (scaling by each condition),
the rest have large clusters but too may activation foci to localize them.
I also tried another approach: GLM scaling option,
grand mean scaling by subject and global scaling of each image.
Localization was best for global scaling as was expected.
Thanks in advance for your help.
Takanori Kochiyama.
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Takanori Kochiyama, Ph.D.
Advanced Telecommunications Research Institute International
Brain Activity Imaging Center
E-mail: [log in to unmask]
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