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Hi - I think you're saying that you have two somewhat similar timecourses; when you in some way averaged them into a single EV you found reasonable activation, but when you separated them, they didn't show separate activations (or anything under the differential contrast). This isn't necessarily surprising if they are similar to each other - assuming they are both accurate models, then you can get back to the 'average' result with a [1 1] contrast - but it they are very similar to each other, all the other contrasts will be very low efficiency (see the efficieny reporting in the FEAT model GUI, and also the Smith NeuroImage paper on efficiency). Cheers. On 5 Nov 2008, at 11:42, Nils Richter wrote: > <[log in to unmask] > > > <[log in to unmask]> > <[log in to unmask]> > Subject: comparing timecourses > To: "FSL - FMRIB's Software Library" <[log in to unmask]> > X-Authenticated: #18468792 > X-Flags: 0001 > X-Mailer: WWW-Mail 6100 (Global Message Exchange) > X-Priority: 3 > X-Provags-ID: V01U2FsdGVkX18ZsK4mvOIZYFi5iUYnGlfDMbo9hx+dHqYFZR9eEG > 0qgVKVapS8eZxUIqFHYbAVJd7E4UOvWAUpgw== > Content-Transfer-Encoding: 7bit > X-GMX-UID: vbQocbcnYW0tXty8eGdp00V8amthc5tR > X-FuHaFi: 0.76 > X-CCLRC-SPAM-report: 0 : > X-Scanned-By: MIMEDefang 2.57 on 130.246.193.104 > > Hi everybody, > > I have a problem regarding the comparison of two different > timecourses. One is the timecourse of stimulus onset and the other > is the timecourse of response onset. Because the time from stimulus > to response varies from trial to trial the shift between the > timecourses ist not the same for each trial. > I want to see if they yield different activation. Now I have run > both timecourses in one EV models and on visual inspection the > activation appears to be somewhat different between the two. > To quantify this difference I have tried to run the two timecourses > as EVs in the following two EV model: > > EV1: stimulus timecourse > EV2: response timecourse > > Contrast 1: EV1=1, EV2=0 > Contrast 2: EV1=0, EV2=1 > Contrast 3: EV1=1, EV2=-1 > > The three contrasts all show very little activation and the > contrasts 1 and 2 bear no resemblance to the contrasts in the one ev > models, which I can't make sense of. > There appears to be some sort of interaction between the contrasts. > Cheers, > Nils > -- > Ist Ihr Browser Vista-kompatibel? Jetzt die neuesten > Browser-Versionen downloaden: http://www.gmx.net/de/go/browser > --------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------