Rick,

Thanks what you say makes sense . Can you clarify which points in the function then correspond to which time points in time? For example is it correct to be assuming that the first point represents signal accumulated from 0-3 s, the next point 3-6, the third 6-9, the fourth 9-12, and the fifth ?....This is where I think I'm not fully understanding the tent function as I though it indicated activity from 12-15 s.

I went ahead and tried TENT(0,21,8) but here again I run into multicollinnearity issues (see below). TENT(0,18,7) works alright.

++ ----- Signal+Baseline matrix condition [X] (544x74): 71.9689 ++ GOOD ++
*+ WARNING: !! in Signal+Baseline matrix:
* Largest singular value=6.38017
* 1 singular value is less than cutoff=6.38017e-07
* Implies strong collinearity in the matrix columns!
++ Signal+Baseline matrix singular values:
-6.81987e-16 0.00123181 0.00529531 0.0218892 0.0363943
0.0524567 0.0568491 0.0865535 0.72654 0.752044
0.810878 0.850482 0.89111 0.957701 0.979728
0.991117 0.996769 0.999603 1 1
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
1 1.00001 1.00014 1.00051 1.00102
1.00169 1.00402 1.01159 1.02593 1.07561
1.09022 1.12613 1.17164 1.239 1.29408
1.3543 2 2.0073 6.38017
++ ----- Signal-only matrix condition [X] (544x56): 1 ++ VERY GOOD ++
++ ----- Baseline-only matrix condition [X] (544x18): 68.6126 ++ GOOD ++
++ ----- stim_base-only matrix condition [X] (544x6): 27.2235 ++ GOOD ++
++ ----- polort-only matrix condition [X] (544x12): 1.07803 ++ VERY GOOD ++
*+ WARNING: +++++ !! Matrix inverse average error = 0.0104015 ** BEWARE **
++ Matrix setup time = 2.90 s
** ERROR: !! 3dDeconvolve: Can't run past 2 matrix warnings without '-GOFORIT 2'
** ERROR: !! Currently at -GOFORIT 0
** ERROR: !! See file 3dDeconvolve.err for all WARNING and ERROR messages !!
** ERROR: !! Be sure you understand what you are doing before using -GOFORIT !!
** ERROR: !! If in doubt, consult with someone or with the AFNI message board !!
** FATAL ERROR: !! 3dDeconvolve (regretfully) shuts itself down !!