Presenting a Sketchpad item, Sampler item and a trigger simultaneously
Hi!
We want to set up a priming study in the lab that I am working for and we want a mask to be presented for 250 ms, a prime to be presented for 50 ms and the target to be presented at the same time as an audio file - and the target needs to be marked. Since this is a priming study, it is critical that the target, audio file and the trigger are all sent exactly 50 ms after the prime has been presented. We have a monitor with a 60 Hz refresh rate and are using OpenSesame 3.0 and the newest version of the parallel port trigger plugin. Given all this, I just wanted to make sure that the following method would be appropriate to attain the required timing precision (and that things like audio jitters and refresh rate wouldn't affect it)
Sketchpad item (Mask) Duration: 250 ms
Sketchpad item (Prime) Duration: 46 ms
Parallel Port Trigger item (Trigger) Duration: 4 ms
Sketchpad item (Target) Duration: 0 ms
Sampler item (Audio) Duration: 300 ms
Sketchpad item (Blank): 500 ms
My reasoning for this was as follows: The Prime would be presented for 46 ms and then because the Trigger doesn't change the screen, the trigger would be presented after 46 ms but then the Prime would still appear on the screen. Then after 50 ms, the screen would change to the Target and then immediately play the audio (because the screen was presented for 0 ms) and then it would stay on screen for the duration of the Audio before then presenting the Blank screen. So therefore, the target and the audio file are always presented exactly 4 ms after the trigger is sent and hence we can just add the 4 ms and we'd have the Target, Audio and Trigger time-locked. Is this reasoning correct? Or would I be "missing the train" with the Target like the Page on Timing in OpenSesame discusses (http://osdoc.cogsci.nl/3.0/miscellaneous/timing/)? Also would audio jitter do anything to mess up the timing accuracy?
Thank you!
Grusha.
Comments
Hi Grusha,
I personally find it always rather hard to say, yes that's correct. In theory, your reasoning sounds okay to me. However, the only way to be sure is testing it. Did you already have the chance to test it (btw, sorry for the late reply...)
Eduard
Hi Eduard!
We did test it and it seems to work! But for some reason, we need to specify the duration of the prime to be one refresh cycle lower than when we want it presented. So for example, when we set the duration of the Prime to anything less 50 (three refresh cycles) but greater than 33 (two refresh cycles), it always "missed the train" and was presented for around 66 to 67 ms instead. However, when we set it to be less than 33, it ended up being presented for around 50 ms - which is what we wanted. Do you know why this is the case?
Thank you!!
Grusha.
Hi Grusha,
Great to hear!. Unfortunately, I am also unsure what could be the reasons for this behaviour. I had similar issues when the timing on my machine were quite off and more importantly not even consistently off. However, when I tested it in the lab it worked right out simply perfectly. So, the system/computer you're using is probably playing a role, but aside from that I don't have much to add to this discussion. Maybe @sebastiaan can help out?
Sorry,
Eduard