Hi Catherine,
If the time window prompt you are talking about is the window length
(xBF.length), then I believe the window is the time it takes for your
function to return to baseline in seconds. I believe a standard value
for FIR is 20-24. However, if you look in the SPM functions
(spm_fmri_spm_ui or spm_fMRI_design) you will see that window length
is overwritten automatically by SPM. If you want to change the decay
function you can try changing the time bin length(xBF.dt), which is
set by SPM as TR/#ofTimeBins. If you want to experiment with this the
easiest way is to change the number of time bins per scan. Careful
when messing with these attributes as it can have a serious effect on
your parameter estimates. If the time window you were talking about
was the duration of the covariate onset, then it seems logical for you
to model the stimulus as an event (duration of 0).
Hope this was helpful,
Michael Rubens
--
Research Associate
Gazzaley Lab
Department of Neurology
University of California, San Francisco
Lab Phone # (415) 476-2164
NIC Phone # (415) 476-4232
Cell Phone # (415) 902-3138
UCSF, Mission Bay
MC2512, 1700 4th st.
Byers Hall, Room 102C
San Francisco, CA 94158
http://gazzaleylab.ucsf.edu/Michael-Rubens.html
On Sun, Apr 6, 2008 at 6:30 PM, Catherine Wan
<[log in to unmask]> wrote:
> Dear SPM -list,
>
>
> I'm writing to seek clarfication on FIR analysis using SPM5. I'm running an
> auditory experiment using a sparse sampling design. The design incorporates
> a silent period, such that the actual interscan interval is 14s, and the
> single volume image acquisition occurs 4s after the stimulus presentation to
> capture peak of HRF (TR = 4.69s).
>
> The basis function I'm using is FIR. In the time window prompt, I've
> entered 4s to allow for the delay between stimulus and image acquisition. Is
> this correct? I've also tried it with other values and the outputs turn out
> to be identical.
>
>
> Many thanks - any assistance will be much appreciated.
>
> Regards,
> Catherine
>
--
Research Associate
Gazzaley Lab
Department of Neurology
University of California, San Francisco
Lab Phone # (415) 476-2164
NIC Phone # (415) 476-4232
Cell Phone # (415) 902-3138
UCSF, Mission Bay
MC2512, 1700 4th st.
Byers Hall, Room 102C
San Francisco, CA 94158
http://gazzaleylab.ucsf.edu/Michael-Rubens.html
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