Thanks for the insight! I personally use always normalized and I do not think that this should matter too much. I think given that normalization introduces some smoothing, it may probably even increase predictions - as Hans Op De Beeck showed that smoothing might be helpful for prediction rate.
On Mon, May 5, 2014 at 10:21 PM, J.A. Etzel <[email protected]> wrote: > I've done both: MVPA in subject space (no spatial normalization), and > after normalization to an atlas. Even for searchlight analysis both are > possible: run the searchlights in subject space and normalize for the > group-level analysis, or normalize first. > > Ideally, it wouldn't matter at which stage of analysis spatial > normalization was done. And it often doesn't seem to matter much in > practice, particularly when working with fairly large ROIs. > > Sometimes working in subject space, with individually-defined ROIs seems > most sensible, for example when a small, definable anatomic structure is of > interest (such as the amygdala or hippocampus). Other times you need to > work with spatially-normalized images, such as when doing a > multiple-subject analysis. > > All spatial normalization algorithms are imperfect, and introduce > additional blurring, distortions, and dependencies into the images. We > accept those distortions for mass-univariate GLM analyses; should we accept > them for MVPA as well? I usually do, hoping that they will be relatively > minor compared to the distortions already added to the data (e.g. movement > correction, slice-timing, scanner drift), and in BOLD itself. > > Do others have different experiences? Ever seen a dataset in which spatial > normalization made a meaningful difference? > > Jo > > > > > On 5/3/2014 9:31 AM, Vadim Axel wrote: > >> Hi, >> >> If one uses functional localizer or selects anatomical ROIs individually >> he might run MVPA in a native space (without spatial normalization to >> template of the data). Have you encountered any paper that compared >> normalized vs. non-normlaized prediction rates? Or probably personal >> observation? Obviously, for search-light one needs to normalize. >> >> Thanks, >> Vadim >> >> >> >> _______________________________________________ >> Pkg-ExpPsy-PyMVPA mailing list >> [email protected] >> http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/pkg-exppsy-pymvpa >> >> > -- > Joset A. Etzel, Ph.D. > Research Analyst > Cognitive Control & Psychopathology Lab > Washington University in St. Louis > http://mvpa.blogspot.com/ > > _______________________________________________ > Pkg-ExpPsy-PyMVPA mailing list > [email protected] > http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/pkg-exppsy-pymvpa >
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