Hi - it sounds from your description like you did things right, so yes I
suspect that the problem is somewhere in the details of the 3-column EV
setups. The best thing to do is to make a tar file of the output FEAT
directory plus the input 3-column text files, and put it on a web/ftp
site and we'll take a look.
On Fri, 29 Oct 2004, Cornelius Werner wrote:
> Dear all,
> I conducted an event related fMRI study, where people had to press
> visually cued buttons and were to evaluate the (visual) result by another
> button press, which could be either the expected one (c for congruent) or
> an unexpected one (ic for incongruent). Sometimes, there were null events
> interspersed (fixation cross only). (Actually, there was one more factor,
> which is of no interest right now).
> During analysis, I was interested in the hemodynamic response to the
> visual presentation of both the expected result, the unexpected result and
> the difference between both. Therefore, I created a "three-columns" design
> matrix with the actual presentation times (in seconds) of the respective
> event, the actual duration (in s) and simply "1" for the weighting factor.
> My contrasts were specified as follows:
> c ic null
> 1 0 -1 Main Effect Congruent
> 0 1 -1 Main Effect Incongruent
> -1 1 0 Differential Activation (ic > c)
> All preprocessing options were left on default (except for slice timing,
> which was turned on).
> The problem now is that there is NOTHING coming up in the results on the
> single subjects level - no higher level visual cortices, simply nil. When
> leaving the data unthresholded, some brainstem lights up, which doesn't
> help too much...
> Now, this really makes me wonder, as the same analysis performed with SPM2
> yields the expected results with not too weak t-values even in the
> differential contrast. So I suppose I did something wrong with the design
> matrix!?! Or are there any other typical pitfalls a beginner might stumble
> into which I am not aware of??
> I'd greatly appreciate your help with this!
> Best regards,
> Cornelius Werner
> Cornelius Werner
> Institut fuer Medizin (IME)
> AG Kognitive Neurologie
> Forschungszentrum Juelich
> 52425 Juelich
> Tel. +49-(0)2461-61-8609
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