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Thanks so much. I will try... Best Regards * Tom Johnstone <[log in to unmask]> [Thu, 2 Apr 2009 12:45:39 +0100]: > On Thu, Apr 2, 2009 at 12:25 PM, Alexander Lebedev <[log in to unmask]> > wrote: > > Thank you very much for anwsers! > > > > Our scanner is Siemens Magnetom Symphony 1.5 T. In our study we use > the > > modification of "Stroop-Task" in order to cause a frustration in > Healthy > > and Depressive subjects. I think that the optimal solution is by using > > the "brainmask", isn't it? > > Also worth considering in that case then is that waiting until after > you've spatially smoothed your data before you apply a mask might be a > mistake, because the smoothing could blur some eye movement signal > into adjacent regions of cortex such as the orbitofrontal cortex that > might be of interest in emotion-related paradigms. So stripping out > the eyes before model fitting might be worthwhile. > > -Tom Johnstone > > > > > > Best Regards > > Alexander Lebedev > > > > * Torben Ellegaard Lund <[log in to unmask]> [Thu, 2 Apr 2009 > 10:52:20 > > +0200]: > >> > >> I completely agree! But then again some scanners suffer from serious > > > > N/ > >> > >> 2 ghosting and then you would actually like to get the aliased eye > >> movements removed from the visual cortex. > >> > >> Best > >> Torben > >> > >> > >> > >> Den 02/04/2009 kl. 10.41 skrev Michael T Rubens: > >> > >> > Perhaps knowing a bit about the type of task would help determine > >> > the best method. For many visual tasks it is likely that the signal > >> > you would extract from the eyes would highly correlate with the > >> > task, thereby regressing out signal of interest and killing your > >> > power. > >> > > >> > -Michael > >> > > >> > On Thu, Apr 2, 2009 at 1:23 AM, Torben Ellegaard Lund > >> <[log in to unmask] > >> > > wrote: > >> > Hi Dorain > >> > > >> > There are several ways this could be done, and which one you choose > >> > should depend on your programming skills. But in general you should > >> > have a pretty good prior hypothesis that the particular area you > >> > want to mask out by regression will be a noise only area. But this > >> > would e.g. apply to ventricles, major blood vessels and eyes. > >> > > >> > One way to do this is to use the Eigenvariate button, when you view > >> > your results. Move the cursor to the eyes, and use the Eigenvariate > >> > button to extract the timeseries from the region, or single pixel. > >> > Now reanalyse your data with the extracted timeseries entered a a > >> > covariate, much like you would do with motion parameters. The > >> > timeseries you want to remove will be found in the variable xY.u > >> > > >> > Alternatively you could find typical MNI space locations for eyes > >> > and ventricles and automatically extract timeseries from those > >> > regions using spm_sample_vol.m This would require a bit of matlab > >> > coding. > >> > > >> > The benefit of regression as opposed to masking is that noise could > >> > be removed from other areas than the ones where you timeseries was > >> > extracted from. The drawback is that you risk removing real signal, > >> > if the noise looks like the signal. > >> > > >> > > >> > > >> > Best > >> > Torben > >> > > >> > > >> > > >> > > >> > > >> > > >> > > >> > Den 02/04/2009 kl. 06.49 skrev Dorian P.: > >> > > >> > Dear Torben, > >> > > >> > How can a time series from a specific voxel be added as a > regressor? > >> > > >> > And can this be done to covary out the activity similar to any > voxel > >> > of artifactual activity? > >> > > >> > Thank you. > >> > Dorian. > >> > > >> > 2009/4/1 Torben Ellegaard Lund <[log in to unmask]>: > >> > > >> > Dear Alexander > >> > > >> > If the eye-artefact is only there in some of the con images it will > >> > not make > >> > it through the threshold in the final second level analysis. This > >> > could have > >> > been the case in a fixed effects analysis but not in a random > > > > effects > >> > >> > analysis. If you want to avoid those artefacts you could include a > >> > time-series from an eye-voxel in your design matrix. This would > most > >> > likely > >> > remove the eye-artefact, but you risk removing some of the activity > >> > as well. > >> > > >> > Best > >> > Torben > >> > > >> > > >> > > >> > Den 31/03/2009 kl. 16.56 skrev Alexander Lebedev: > >> > > >> > Dear SPM experts > >> > > >> > I decided to check my old results, and found one problem. When I > > > > have > >> > >> > opened con*-files in xjview tbx, strange thing appears... There are > >> > activations of eye movements (notwithstanding of Normalization) in > >> > some > >> > con*-files. May I include such results in group study? Could you > >> > advice me > >> > any solutions to prevent this trouble? > >> > > >> > Thank you beforehand > >> > > >> > Best Regards > >> > -- > >> > Alexander Lebedev. > >> > > >> > > >> > > >> > > >> > -- > >> > Research Associate > >> > Gazzaley Lab > >> > Department of Neurology > >> > University of California, San Francisco > > -- Alexander Lebedev.