By definition, SPM.xBF.order must be 2 for including the time derivatives, 3
if you include the time and dispersion.
Thus, your contrast has 2 rows in it. This makes it invalid for a
T-contrast. You can either change the contrast type to an F, or change the
contrast.
However, you can't use an F-test from the first-level at as the inputs for
the second-level. Additionally, the average the HRF and time derivative
isn't measningful. If you are looking at trying to come up with an
integrated method for the HRF and time derivative to use at the second
level, I would recommend that you read Steffener et al.(Investigating
hemodynamic response variability at the group level using basis functions)
or Calhoun et al. (fMRI analysis with the general linear model: removal of
latency-induced amplitude bias by incorporation of hemodynamic derivative
terms).
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Office: (773) 406-2464
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On Sun, Aug 14, 2011 at 5:51 AM, gj <[log in to unmask]> wrote:
> Hi,
>
> I'm running a Matlab script (largely based on the one by Rik Henson) to do
> 1st level analysis in SPM 8, with an HRF w/time deriv basis set:
>
> SPM.xBF.name = 'hrf (with time derivative)';
> SPM.xBF.order = 1;
>
> which results in the following error:
> "Error using ==> spm_FcUtil at 216
> trying to define a t that looks like an F"
>
>
>
> I did
> dbstop error
> before the run to see what gets passed to spm_FcUtil, but not sure what I'm
> looking for.
>
> The same general code runs with no errors when modeling with HRF only (no
> time derivatives), so I suspect that I'm not modifying the code and hence my
> contrasts correctly for time derivatives? I notice that even though I
> specify "SPM.xBF.order = 1;" that along the way, SPM.xBF.order = 2. Here is
> the snippet of code that might be culprit. The "nusr" is for the nuisance
> regressors (bad spikes, movements)
>
> ***** begin snippet *****
> eb = eye(SPM.xBF.order);
>
> cnam{1} = 'contrast1';
> cwgt{1} = [kron([1 0 1 0],eb) zeros(size(eb,1),nusr)];
> ctyp{1} = 'T';
>
>
> ...
> for c = 1:length(cnam)
> clear cw;
> cw = [cwgt{c} zeros(size(cwgt{c},1),1)]';
> spm_FcUtil('Set',cnam{c},ctyp{c},'c',cw,SPM.xX.xKXs);
> end
>
> ****** end snippet *****
>
>
> Any help much appreciated!
>
> g
>
