Thanks Michael for this information! Definitely good to know and I will try it out.
Best, Frances On Sun, May 10, 2015 at 9:40 AM, Michael Hanke <[email protected]> wrote: > FYI: the stelzer algorith is now available in PyMVPA. > > Michael > On May 10, 2015 14:28, "Christopher J Markiewicz" <[email protected]> wrote: > >> On 05/09/2015 12:49 PM, Jingwen Jin wrote: >> > >> > Hi MVPA experts, >> > >> > I have a general question about conducting group-level analysis on the >> > subjects' classification accuracy maps. Let's say I am doing a >> > one-sample t-test to find the voxels that have high classification >> > accuracy across subjects. Essentially, I am doing a t-test on percentage >> > numbers (SVM classification accuracy measured as percentage correct). >> > Since percentage is highly affected by the testing example numbers, and >> > in general would probably not meet the normal distribution assumption >> > for t-test. >> > >> > So my question is if people adjust for testing trial numbers or any sort >> > of transformation? For example, I converted each voxel's percentage >> > number to a z score at the individual subject's classification map >> > level, and then do group-level t-test on these z score maps. I wonder if >> > this is valid? >> >> What you describe sounds like the strategy used by Lee et al (2012) >> <https://dx.doi.org/10.1523/JNEUROSCI.3814-11.2012> so there's >> precedent. On the other hand, it's not clear to me how to do cluster >> thresholding for multiple comparisons correction properly, using this >> method. They use SPM8's random effects analysis, but if I recall >> correctly that requires smoothness assumptions, while MVPA analyses >> typically use unsmoothed volumes. >> >> There's also a much more intensive non-parametric test used by Stelzer >> et al. (2012) <https://dx.doi.org/10.1016/j.neuroimage.2012.09.063>, but >> it requires a lot of computing time and at least temporary storage space. >> >> -- >> Christopher J Markiewicz >> Ph.D. Candidate, Quantitative Neuroscience Laboratory >> Boston University >> >> >> _______________________________________________ >> Pkg-ExpPsy-PyMVPA mailing list >> [email protected] >> http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/pkg-exppsy-pymvpa >> > > _______________________________________________ > Pkg-ExpPsy-PyMVPA mailing list > [email protected] > http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/pkg-exppsy-pymvpa > -- Jingwen Frances Jin Department of Psychology Stony Brook University
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