Sorry, I’ll clarify. The response window is meant to be of a fixed duration: in case of a fast answer, there is padding time until that duration is reached, and in case of no response the script moves on. (I am in fact not quite managing to achieve this aim with the RatingScale component - see separate thread).
The durations of the different epochs in the script (present stimulus, answer, ISI etc) are linked to the scanner’s TR, and so if the total running time of the script were that obtained by summing up all theoretical durations (number of blocks X duration of one block), the script-scanner sync should be fine. But I have been warned by our MR physicist (and the thread I linked to before confirmed it) that with each trial/block, PsychoPy may accumulate some delays that in the end make the total duration greater and thus desync the acquisitions with the intended epochs they were meant to refer to.
My question was how to counter this effect - whether the lags can be taken into account posthoc or whether some “wait” trigger needs to be inserted in the script at block/trial level - although that assumes the actual duration would be less, rather than greater than the theoretical duration.