Hi Steve,
thanks for your input. I also realized that Feat runs on the raw
COPEs, thanks a lot for confirming it. And no, the EV1>0 contrast does
not activate here. So it seems to be true that this interaction is not
being driven by Task A / stimulus O, but the inverse (i.e. Task J /
stimulus W). This is something we did not expect for that region in
particular, but such is life - always full of surprises...
Best regards and many thanks,
Cornelius
On Wed, Jun 1, 2011 at 10:09 AM, Stephen Smith <[log in to unmask]> wrote:
> Hi - I'm not quite following - are you looking in a region that passed the
> EV1>0 contrast? In this case the COPE [1 0] would not be negative.
> Cheers.
>
>
>
> On 31 May 2011, at 09:59, Cornelius Werner wrote:
>
> Hello list,
>
> I am having a look at some PET data, where we had four conditions
> (Task A and J combined with stimulus O and W -> conditions AO, AW, JO,
> JW). 14 subjects were scanned with no baseline. Each condition was
> repeated three times (=12 scans/subject). I analyzed single subjects
> first and performed a group analysis as a 2nd level design.
> On the first level, tasks and stimuli were orthogonal, i.e. the
> timecourse of task A was -(timecourse of task J). Thus, i created two
> EVs, EV1 for task A and EV2 for stimulus O. Main effects were defined
> as:
>
> EV1 EV2
> 1 0 task A
> -1 0 task J
> 0 1 stimulus O
> 0 -1 stimulus W
>
> Results are very reasonable for the main effects. However, I am more
> interested in the interaction of task A and stimulus O, i.e. the
> neuronal correlates of task A particularly when triggered by stimulus
> O. I therefore added a third interaction EV encompassing contrasts 1
> and 3 [1 0; 0 1], setting "make zero: min" for both. The resulting
> regressor is "on" only for the AO-condition, as intended (see attached
> design matrix image). Results are in a anatomically plausible and
> expected region. However, and this is my problem, the COPEs given by
> Featquery are just the other way round as I imagined them to be! In
> this region/z-thresholded mask (and for the max peak) they are
> something like -300 +300 -420 +420 (for A, J, O and W, respectively) -
> that is, just the negative of the expected pattern. I can't get my
> head around this - can anyone help me out of this?
>
> Many thanks in advance and best regards,
> Cornelius
> --
> Dr. med. Cornelius J. Werner
> Department of Neurology
> RWTH Aachen University
> Pauwelsstr. 30
> 52074 Aachen
> Germany
> <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
> ---------------------------------------------------------------------------
>
>
>
>
--
Dr. med. Cornelius J. Werner
Department of Neurology
RWTH Aachen University
Pauwelsstr. 30
52074 Aachen
Germany
|