 |
 |
Hi - that probably makes sense, yes. The images on your web page aren't viewable; however, you should probably judge mean abs difference in unthresholded zstat images rather than looking at the extremes. Cheers, Steve. On Fri, 25 Jun 2004, Zrinka Bilusic wrote: > Hello, > thanks for your reply... > > I actually did find an error in the registration part of the analysis. > I was moving files from one computer to another and then the links in > *.feat/reg folders got broken. I wrote a script to change them, but I > did not doublecheck the hires files for each subject and I linked some > to the wrong images. That's why the background image seemed "wrong". > After I fixed that, the registration was fine, but the statistical > results remained "different". Now I had no "activations" above the > threshold in the group analysis. When comparing "old" (I am referring > to the one before the current version of feat: I believe that was 3.0?) > to corresponding "new" zstat files, I noticed that the results are not > "completely different" (as I mentioned earlier and as one of the > questions you pointed to states). Instead, it seems that the > distribution of "activations" is more or less the same, except there is > less of it and the z values are consistently lower. For example, the > old zstat file that had a max/min values around 5/-5, the new one > showed them to be around 2.5/-2.5. You can see an example of that at > http://nina.bmap.ucla.edu/ That is quite a big difference! But based on > the links you sent, I guess that is not unusual? > > thanks > zrinka > On Jun 25, 2004, at 7:49 AM, Stephen Smith wrote: > > > Hi Zrinka, > > > > Wrt registrations and background image, yes if you are only re-running > > higher-level analysis then the old registrations will have gotten used > > and > > not rerun. The background image may have changed because I think we > > added > > in between the current and previous versions a flag to normalise the > > background images to all have the same mean intensity before averaging > > - > > just a display nicety, really. > > > > Wrt the stats, which "old" version are you comparing with? If it's 3.0 > > then maybe this is answered at: > > http://www.jiscmail.ac.uk/cgi-bin/webadmin? > > A2=ind0310&L=fsl&P=R5762&D=0&H=0&I=-1&O=T&T=0 > > and > > http://www.jiscmail.ac.uk/cgi-bin/webadmin? > > A2=ind0403&L=fsl&P=R517&D=0&H=0&I=-1&O=T&T=0 > > ? > > > > Cheers, Steve. > > > > > > On Wed, 23 Jun 2004, Zrinka Bilusic wrote: > > > >> Hello, > >> > >> recently I decided to rerun group analysis on some old data. The > >> reason > >> was that the original group analysis was done using the old version of > >> Feat, and I wanted to see the additional reports from the new version > >> of Feat (the Summary of low-level registration and masks). So I loaded > >> the design.fsf into Feat, changed the output directory, verified that > >> everything is OK, saved and run. But the (statistical) results are > >> different. No only in the report, but I also subtracted zstats images > >> - > >> and there are big differences. I inspected the design.fsf files, and > >> the only difference I could find (apart from the obvious differences > >> in > >> the layout for new and the old versions) is that in the new design.fsf > >> file, the degrees of freedom to standard image was set to 7, whereas > >> in > >> the old one it was 12. But that should not cause any problems because > >> the registrations were already calculated in the single subject > >> analyses, and the first step of the group analysis just applies those > >> transformations - right? > >> > >> Also, I notices that the background image for the two analysis looks > >> quite different - even though in both design files it was set to the > >> "mean highres". I looked at the log files and the commands executed to > >> create those seem to be the same. > >> > >> Am I missing something? The statistical results should not be > >> different? Is there anything else I should be checking? by the way, > >> the > >> single subject analyses were not changed after running the initial > >> group anlaysis... > >> > >> thanks > >> > >> zrinka > >> > > > > Stephen M. Smith DPhil > > Associate Director, FMRIB and Analysis Research Coordinator > > > > Oxford University Centre for Functional MRI of the Brain > > John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK > > +44 (0) 1865 222726 (fax 222717) > > > > [log in to unmask] http://www.fmrib.ox.ac.uk/~steve > > > > > Stephen M. Smith DPhil Associate Director, FMRIB and Analysis Research Coordinator Oxford University Centre for Functional MRI of the Brain John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222726 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~steve