Stimuli getting longer and longer as the experiment goes

Hey everyone!

On my computer and online, everything works well, my stimuli keep the same length during the whole experiment. My computer is 60Hz and my frames were coded accordingly.

However, I just connected it to the BOLD screen on the MRI machine (which is 120HZ, so I doubled the number of frames for the time of presentation), and now, after 50 presentations, the frames are getting longer and longer. So for instance, for 50 stimuli it’s 33ms, then for another 50 it’s 46ms, and for another 50 it gets to 90ms. All my other stimuli are getting longer and longer as the experiment goes.

Did it already happen to one of you?

What should I do? It is very annoying !