How to create response window for n-back task (case 10630)

[Heather]

Hi,
I am working on creating an n-back task, and have looked at some of the helpful samples in other forums. I am running into a problem in creating my specific version of the task. I want to display a stim (letter) for 1500ms and then have a 500ms blank screen before moving to the next trial. I would like for participants to be able to respond (or, no response) at any point during the 2000ms without altering the length of the stim or blank screen. (In other words, the trial should have a 1500ms stim and 500ms blank screen, regardless of whether the participant responds or not).

I have tried many combinations of minmax values, full/clear, and -1 codes to try to accomplish this, but can't quite find the right combination. Attached is the current attempt, which has the 1500ms stim window (but not the 500ms extended response window). Any ideas? Thanks in advance!
--Heather