Dear Rick,

Thanks for your help and explanation, it really helps.

-How many time points are there?
Each trial lasted 8, 9 or 10 seconds and was divided in 3 within-trial events: “q” (3 sec), “c” (2, 3 or 4 sec) , “o” (3 sec).
For event “q” we had two possibilities/regressors (“qs” or “qo”), same for regressor “c” and for event “o” we had 4 possibilities/regressors (“ood”, “oou”, “osd”, “osu”). We had 32 trials per run (2 runs in total). TR=2.

-How many regressors in the TENT case?
I added as many regressors as I had for the dmBLOCK because it was my understanding that each within-trial event needed to be included (even though I’m mostly interested in what happened during event “o”). The text stimfiles for the TENT function consisted of one row per run with the event onsets in seconds. Here how it looks:

-stim_times 13 ${stim}/.. 'TENTzero(0,12,7)' -stim_label 13 'qo' \
-stim_times 14 ${stim}/.. 'TENTzero(0,12,7)' -stim_label 14 'qs' \
-stim_times 15 ${stim}/.. 'TENTzero(0,12,7)' -stim_label 15 'co' \
-stim_times 16 ${stim}/.. 'TENTzero(0,12,7)' -stim_label 16 'cs' \
-stim_times 17 ${stim}/.. 'TENTzero(0,12,7)' -stim_label 17 'ood' \
-stim_times 18 ${stim}/.. ’TENTzero(0,12,7)' -stim_label 18 'oou' \
-stim_times 19 ${stim}/.. ’TENTzero(0,12,7)' -stim_label 19 'osd' \
-stim_times 20 ${stim}/.. 'TENTzero(0,12,7)' -stim_label 20 'osu' \

Do you think that the duration was defined incorrectly? Should the duration relate to each regressor duration instead of the whole trial duration?

How "random" is the timing and ISI?
ISI was either 2, 3 or 4 seconds.

Thanks for your assistance!
Irene