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Hey Regina, In one sentence, the question is: is a *within-subjects* residualization > procedure (routinely part of fsl) sufficient to control for individual > differences in EV2 statistical maps when running a voxelwise regression > *across subjects* on EV1 statistical maps? > If I follow you, no - it is feasible to model uninteresting cross-session variation in a contrast of interest by including a regressor reflecting the cross-session variation of some control condition performed in the same run. It may be feasible to do this using a voxel dependent EV. I've been trying something similar myself. Cheers, Eugene > Thanks much for any clarification or recommendations, > > Regina > > > On Wed, 29 Apr 2009 09:55:46 +0100, Mark Woolrich <[log in to unmask] > > > wrote: > > >Hi Regina, > > > >It sounds like you want to know how, within a voxelwise GLM containing > >2 EVs, you can find only the explanatory power associated with (i.e. > >variance explained by) EV1 above and beyond EV2 and vice versa. The > >answer is that when you do [1 0] or [0 1] contrasts the GLM will > >automatically take care of this for you. For example, if the EVs are > >partially correlated then the GLM fitting of the parameter estimate > >for EV1is only driven by the component of EV1 that is orthogonal with > >(uncorrelated to) EV2 - and the resulting statistics will > >automatically reflect this accordingly. > > > >Cheers, Mark. > > > >---- > >Dr Mark Woolrich > >EPSRC Advanced Research Fellow University Research Lecturer > > > >Oxford University Centre for Functional MRI of the Brain (FMRIB), > >John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK. > > > >Tel: (+44)1865-222782 Homepage: http://www.fmrib.ox.ac.uk/~woolrich<http://www.fmrib.ox.ac.uk/%7Ewoolrich> > > > > > > > > > >On 29 Apr 2009, at 02:45, Regina Lapate wrote: > > > >> Dear all, > >> > >> I have a question that I can imagine two potential ways of answering > >> it, and > >> while I am comfortable with how to implement it the first way, I > >> would like > >> to know if there is a practical way to implement it the second way > >> (in fsl). > >> The question is: > >> > >> - If one wants to residualize brain activation associated with > >> condition A, > >> from brain activation associated in condition B... > >> > >> 1) In a ROI approach, I assume one can extract parameter estimates > >> associated with BOLD changes due to condition A (cope1), similarly for > >> condition B(cope2), and regress cope1 on cope2 using a statistical > >> program > >> while saving the residuals of this regression; > >> > >> 2) But what about in a voxel-wise GLM approach in fsl, where both > >> conditions > >> A and B are EVs in the model? Is there a practical way where fsl can > >> save/output the residuals that remain after accounting for the > >> variance > >> associated with condition A, so that I could look at the variance B > >> accounts for once variance due to A has been removed? > >> > >> Thanks much for any suggestions! > >> > >> Regina > >> > -- Eugene Duff Centre for Functional MRI of the Brain (FMRIB) University of Oxford John Radcliffe Hospital, Headington OX3 9DU Oxford UK Ph: +44 (0) 1865 222 523 Fax: +44 (0) 1865 222 717 --