judgment of contingency task

Hi there. I'd like to run a judgment of contingency task in Direct RT and am having a little trouble with it, as I am not sure how to set it up so that a specific response is required / not required BEFORE the next stimulus is presented. I've used Direct RT to code a stroop task before without any trouble, but this is the first task I'm trying to code that requires presentation of a stimulus (stim2) being contingent on responses made to stim1.

There will be 40 trials in all. Essentially, respondant are all presented with a 'fixation' stimulus (a yellow square) on all 40 trials. WHILST the square is displayed, they have the option of either pressing or not pressing a space bar. On a specified number of trials (30), a green triangle will follow the yellow square; and 75% of the time, pressing the space bar needs to result in displaying a green triangle. The other 25% of the time, the green triangle will be displayed regardless of whether the space bar is pressed or not. For the remaining 10 trials, the green triangle is not presented at all.

Is this possible to achieve in Direct RT? (please tell me it is!! :P) - I'm at a bit of a loss to figure out how to code this up... any advice would be much appreciated, I'd love to get this up and running soon. thank you for your help!