Voxel size differences in R and L maskers

[atsuch]

This is rather a fine point, but the hemi-maskers are not equal size, I think because R-hemi includes some voxels at the mid slice, and L-hemi doesn't.

This means that when we compare the spatial similarity of R and L by flipping one image, the results will be slightly different based on the choice of hemisphere masks. I know that the contribution of those mid voxels are minor, but it does affect matching etc. It might also influence ICA results slightly, depending on how much those voxels contribute to the components.

Given that we don't know which hemisphere they actually belong to, I'm inclined to remove those mid-slice voxels from either hemi-maskers/masks, but what do you think @bcipolli?

[atsuch]

I take it back... it's not the mid-slice voxels, but simply the different size of R and L hemispheres in MNI template, and I found a mistake in my code that was comparing the outcome of dissimilarity matrix using R or L hemi mask. They are more or less the same, and I don't think the difference would affect any of our analyses. Still, I wonder if we should resample data to symmetrical template and also use hemi masks based on the same template? It would obviate the need to adjust for different number of voxels in some parts of the analysis too. What do you think? Do you see any potential problem with resampling data to symmetric template?

[bcipolli]

I think it's a good detail to consider.

Would we have to build such a template ourself, or are there symmetric templates out there?

I think some of our analyses (where we do not compare R&L, but instead wb:R to R-only:R) should stick with an asymmetric template (which is more representative of the brain), but if there are good options available for comparing R&L using a symmetric template, we should definitely explore doing so.

[atsuch]

http://www.bic.mni.mcgill.ca/ServicesAtlases/ICBM152NLin2009 2009c is the latest one, I think. We just need to down-sample it to 2x2x2mm.