James,

> I'm still confused about whether it is justified to ignore any pre-stimulus anticipatory effects, which
> is what TENTzero seems to do. And yet, at least in my case the stats come out the same, it's really
> just a question of how the plotted responses look.

If you believe that anticipation effect may exist, go with TENT. If TENT(0, ...) is not good enough to catch longer anticipation, use a negative number such for the first parameter in TENT.

> Could you explain to me, more generally, why TENTzero exists? That is, what was the motivation for
> adding it to AFNI in the first place? If I understood that, perhaps I could answer my own questions.

If you don't expect any anticipation (nor stimulus timing errors) for your trials, use TENTzero. In other words, TENTzero is basically like the shape-fixed approach with GAM or BLOCK in terms of stimulus onset times with the assumption that BOLD response starts at the moment when each stimulus begins.

Gang