Hello,
Your interpretation seems correct.
Note that TENT(0,20,20) will not be TR-locked. You probably want TENT(0,20,21), and Gang would suggest using TENT(1,19,19), to omit time points for which you expect the betas to be zero.
The 20-second interval from 0 20 needs 21 betas to include the end points, measured at times 0..20 (so 21).
As you thought, the duration modulation part of the stimulus is indeed being treated as amplitude modulation, because it is not possible to use DM with TENTs. Doing so would mean either spacing the 21 knots at varying time points or using a variable number of knots, either of which would alter the interpretation of the betas across events. The program does not give a warning or error, because it has a liberal interpretation of the punctuation, applying as "seems appropriate".
- rick