Project sources order question


I have a question about the type of files I should use to project sources to default anatomy.

In order to perform group analysis, the approach in the tutorial is to project the individual source file to a default anatomy. My understanding is that after I project all the individual source files to the same default anatomy, I can then, for example, obtain FFT from each subject's source file in the group analysis folder, and then perform group level analysis on those FFTs.

I noticed that I can also do this in the opposite order, meaning first obtaining FFT using each subject's own source file, then project everyone's FFT file to a default anatomy.

I have compared the FFT (whole brain FFT in my case) files obtained with these two different orders. The two FFT files look very similar, but not exactly the same.

My question is does it matter at which stage I project sources to default anatomy?

Thank you very much!

The two processes (project on template, compute FFT power) are both non-linear, and can't be exchanged.
The idea of the two orders is the same, so you expect similar results, however the slight smoothing occurring when projecting between cortex surfaces would perform differently whether you are processing rectified dSPM source maps or PSD maps, therefore you can't expect strictly equal results.

I recommend you follow strictly the pipelines documented in the online tutorials, and most importantly that you use exactly the same sequence for all your subjects.