Hi Steve,
My experience has been that if you have an empty EV in the first level,
then you must make note of that and make sure to exclude that session
from your higher level analysis, otherwise your higher level cope will
be all 0's. It would be a great new feature if FEAT could be modified
to detect such situations during higher-level analyses and automatically
"ignore" such sessions :)
cheers,
-MH
On Thu, 2011-09-22 at 08:36 +0100, Stephen Smith wrote:
> Hi - yes that all sound ok. For the "empty" subjects hopefully the
> higher-level FEAT will deal with this ok - if not, remove them.
> Cheers.
>
>
>
> On 19 Sep 2011, at 23:15, Michael Klein wrote:
>
> > Hi all and thanks in advance for your help!
> >
> > I have a design that calls for a rest condition (un-modeled), a
> > control condition, and an experimental condition that can be split
> > up according to whether subjects got the behavioural task correct
> > (the vast majority of the time) or incorrect.
> >
> > At the moment, I have a separate FSL EV column file for control;
> > experimental (correct); and experimental (incorrect). Using that
> > same ordering, my contrasts are:
> >
> > [-2 1 1] -> Exp>Ctrl
> > [-1 1 0] -> Exp (correct only) > Ctrl
> >
> >
> > I have two questions:
> > (1) Is it appropriate to run the first contrast like this,
> > considering that experimental (incorrect) trials are fairly rare
> > (i.e. only a couple per run, compared to dozens of exp-correct
> > trials)?
> > (2) Occasionally I get a subject who has 100% correct performance,
> > making the matrix column for exp-incorrect entirely full of 0s. FSL
> > complains, saying that the matrix is rank deficient ("one of my EVs
> > is a linear combination..."). However, it still proceeds to run the
> > FEAT analysis and everything looks okay. Is it kosher to go forward
> > like this?
> >
> > Best and thanks again,
> > Mike
> >
> >
>
>
> ---------------------------------------------------------------------------
> 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
> ---------------------------------------------------------------------------
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