Hi Alex, I'm a little confused by this question - if you have a TR of 2, a
window of 16, and ask for 8 FIR impulses, you should get exactly that,
convolved by the basic shape timing you put in. Note that if your basic
shape is of non-very-small width, this may appear confusing as that width
would contribute to the final waveform. So you might need just to change
the origial shape time width to say 0.1s.
Cheers, Steve.
On Wed, 15 Jun 2005, KORB,ALEX S wrote:
> I want to create an FIR model so I can look at the brain response to an
> event for 8 timepoints following the event at 2 second intervals. What
> I'm concerned about here is an off by one error. I want the first
> impulse to be at the time of the event. At first I thought I would set
> this up in the FIR model as Number=8 and Window=16s. However, if the
> first impulse is at t=0, then the 8th impulse would be at t=14. So
> should I set the window to be 14s? I just want the first impulse to be
> at t=0 and for them to be spaced 2 seconds apart, but I'm not sure how
> FEAT calculates it. Just want to make sure I get it right. Thanks, Alex
>
--
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe 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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