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Hi On 4 Aug 2011, at 01:02, Laura Chaddock wrote: > Hi! > > I am following up on our questions, in response to Steve Smith's suggestions. Thank you for your help! > > 1. I have reattached our current model. I think that we will need to alter the model in order to do contrast masking, as our current model cannot create a contrast that tests for group differences at pre-test. What do you suggest? Indeed - you need different regressors for that - I suggest just having only 4 EVs for this, preP / preC / postP / postC. > > 2. We are unsure of the model to use to create the mask we need. Is there a straightforward way to *exclude* voxels in an analysis? To our understanding, contrast masking and pre-threshold masking determine the voxels to *include.* If you use the new model to do (e.g.) preP-preC, you can threshold that and use as a mask for re-running the original model. Cheers. > > Much appreciated, > Laura > > > ---------- Forwarded message ---------- > From: Laura Chaddock <[log in to unmask]> > Date: Sun, Jul 31, 2011 at 1:35 PM > Subject: Re: [FSL] Longitudinal GLM > To: FSL - FMRIB's Software Library <[log in to unmask]> > > > Hi! > > Thanks so much for your reply. > > 1. I have reattached our current model. I think that we will need to alter the model in order to do contrast masking, as our current model cannot create a contrast that tests for group differences at pre-test. What do you suggest? > > 2. We are unsure of the model to use to create the mask we need. Is there a straightforward way to *exclude* voxels in an analysis? To our understanding, contrast masking and pre-threshold masking determine the voxels to *include.* > > Thanks again for your help! > Laura > > > On Fri, Jul 29, 2011 at 11:41 AM, Stephen Smith <[log in to unmask]> wrote: > You can apply masking from one contrast to another, but you need to be careful that you do not end up making a statement about a difference (or a difference of differences) without explicitly *testing* that statement via the appropriate contrast. > > Cheers. > > > > On 29 Jul 2011, at 03:17, Laura Chaddock wrote: > >> Dear FSL Experts, >> >> I am running an analysis to examine changes in fMRI activation as a function of a 9-month intervention. There are two groups of people (Group A and Group B), and each person is scanned twice (Pre-Test and Post-Test). I have attached our first attempt at the GLM. >> >> We specifically aim to examine where the pre-test and post-test *difference* is different between groups, but we do not want to examine regions where the groups differ at pre-test (as the groups *should* show similar activation at pre-test before being randomly assigned to Group A and Group B). >> >> Can you provide any insight? >> >> Many thanks! >> All my best, >> Laura >> >> >> <design.png> > > > --------------------------------------------------------------------------- > Stephen M. Smith, Professor of Biomedical Engineering > Associate Director, Oxford University FMRIB Centre > > FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK > +44 (0) 1865 222726 (fax 222717) > [log in to unmask] http://www.fmrib.ox.ac.uk/~steve > --------------------------------------------------------------------------- > > > > > > <design.png> --------------------------------------------------------------------------- Stephen M. Smith, Professor of Biomedical Engineering Associate Director, Oxford University FMRIB Centre FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222726 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~steve ---------------------------------------------------------------------------