I’m using PsychoPy to prepare an oddball paradigm in which I preset a picture on the screen for 7 seconds and during the picture presentation 14 consecutive sounds are displayed every half a second. For every sound onset I send a trigger to the parallel port. I then ran timing tests to see whether the sounds are played at the same time as the triggers.
While the triggers seem to be fine and arrive every half a second, this is not the case for the sounds. The sounds are played with a delay of 100ms-200ms after the trigger and the difference between consecutive sounds’ onsets is not half a second. The size of the sound file doesn’t make a difference and the delays seem to be the case both for very short sounds (10ms) and longer ones (250ms). I tried to add ISI at the very beginning of each trial and load both a picture and the sounds during that period but it didn’t help.
I also tried to add the ISI before every sound and load the sounds during these shorts ISIs but it didn’t help either. Do you have any idea how the problem could be solved? Is there any way ISI could help? Am I supposed to have one ISI at the beginning of the trial to load all the stimuli for that trial or multiple ISIs per trial, one per stimulus?
I’d appreciate your help very much. By the way, the delay for the visual stimulus (i.e. the picture) is small and constant across trials.