Hi Todd,
you'll find the stimulus function in SPM.Sess(s).U(u).u for session s and
condition u. However, this is still in microtime onset, which is not the
resolution of your TR. The regressor (ie. the stimulus function is
convolved with the basis function) is created in a much higher temporal
resolution and is then resampled to match your TR.
The relevant code to look at is:
spm_fMRI_design:
1. calls spm_get_bf: create basis function
2. calls spm_get_ons: to get onset and create stimulus function
3. calls spm_Volterra: to do Volterra interactions and convolve stimulus
function with basis function
4. resamples convolved regressor to match the TR and include in design
matrix X (line 280 in spm_fMRI_design)
% Resample regressors at acquisition times (32 bin offset)
%-------------------------------------------------------
try
X = X([0:(k - 1)]*fMRI_T + fMRI_T0 + 32,:);
end
Hope this helps,
Jan
Todd Penney wrote:
> Hello,
>
> I am just wondering if it is possible to get a hold of the stimulus
> function in variable form from the SPM output? I am using the canonical
> function, but I would like to be able to use the stimulus function and
> impulse response function that are convolved together to get the
> canonical response.
>
> Thank you
>
> Todd Penney
>
--
Jan Gläscher, Ph.D. Div. Humanities & Social Sciences
+1 (626) 395-3898 (office) Caltech, Broad Center, M/C 114-96
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