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Timing of the the audiovisual stimulus

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JoeClark
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MessagePosté le: Jeu 26 Oct - 06:36 (2017) Sujet du message: Timing of the the audiovisual stimulus Répondre en citant

Hi! I'm trying to create an experiment that has two conditions: (1) Auditory oddball paradigm and (2) Audiovisual oddball. For the auditory oddball condition, I used the ERP experiment created by Presentation. I wrote similar codes for Audiovisual oddball by adding visual stimuli. After I ran the experiment, I found that the timing for the audiovisual oddball has a lag and I do not know how to fix it. Your help will be highly appreciated! 


After I ran the experiment and looked at the log file, I found that there is a lag time for the audiovisual oddball. For the audiovisual oddball, the required duration of the auditory stimulus is 200ms and the visual stimulus is 300ms. The auditory stimulus and visual stimuli are presented in parallel and played at the same time. When I checked my log file, I found that the actual duration of the visual stimulus is about 330ms (note: auditory and visual stimuli started at the same time). I requested 400ms for the ISI but the actual duration of the ISI is about 470ms. Together, each trial (ie, 330 stimulus +470 ISI) 800ms lasts while the intended time is 700ms (300 Audiovisual + 400 ISI).


Then I checked the auditory oddball condition, and it looks fine. The auditory stimulus is the same one in the audiovisual MMN (200ms). The ISI for 500ms so that the trial length (stimulus + ISI) is 700ms, equivalent to the audiovisual MMN trial. When I checked the log file, the current time for the auditory stimulus is about 215 ms and the ISI is about 535ms. I think this time lag (50ms) is acceptable. 


The laptop screen I used is HP model P1230 CRT CNV4370077 and the refresh rate is 60Hz. Do you have any suggestions on how can this issue lag in the audiovisual condition? I read other threads about timing issues and I wonder if I should simply adjust the request for the duration of the visual stimulus. 




Thank you !!!




I did not find the right solution from the Internet.
References
https://www.neurobs.com/menu_support/menu_forums/view_thread?id=10457
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