If you were going to try to use FIR and treat this as an event-related design - which I strongly discourage -- you would set the window to about 20-30s. The window is the length of the hemodynamic response for each trial. The number of bins represents the number of time points that you sample across the window. Keep in mind, when you use FIR, you need to have trials that begin at different points to sample each bin.
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 Mon, Feb 20, 2012 at 8:13 PM, Zuyao Shan
<[log in to unmask]> wrote:
Dear SPMers:
I am trying to model fMRI data using basis function of FIR (finite impulse response). I have experiments of 16 alternating blocks of condition A and B. Each block is made up of 16 trials. Each trial has 0.2s stimulus presentation and 0.8s gap.
I set up the FIR window length of 0.8s and the order of 1. For the first level model, I used contrast of t-test (–1 1 0) to see condition B – condition A. I did not find any signifiant activations. However, if I perform the same analysis using canonical
HRF with time derivatives and dispersion, there are several regions are activated. I guess there is somewhere wrong for my FIR set up. Any one could shed some lights on?
Thanks in advance!