[PD] Syncing an event with refresh rate in GEM

Batuhan Bozkurt batuhan at batuhanbozkurt.com
Thu Oct 11 18:42:34 CEST 2007


A friend from our schools psychology department wants to use PD and GEM 
for an experiment. Here is his question and attached is the example 
patch. We need you help on this. Thanks.


OK, this is the patch that I'm going to use to conduct a research on 
cross-modal interactions in human perception. I'd be happy to fill 
anyone in on the topic because generally human cognition is fun to poke 

So the required stimuli are a "beep" sound (which is a 3.5khz sine with 
7 ms duration) and a "flash" (which is basically a white circle visible 
only for 20ms).

The problem is, it is very hard for an object to "flash" with this short 
duration. If you look at the patch you'll see that less than 50% of the 
trials do not produce anything.

I have to come up with a workaround to this and I thought maybe if I can 
syncronize the onset of the flash with the refreshing rate, I can at 
least make the disk visible for all of the trials. I can sacrifice the 
precision in terms of duration but that is bound to happen I guess.

I made this patch on windows with my laptop with a poor refreshing rate 
and another laptop with Macosx did not perform any better on the 
task(they are both 60hz screens). But I am guessing that a non-lcd 
monitor may do better? Any comments or suggestions on this?

Relevant information on the stimuli and the procedure can be found in 
this reference article for those of you who are interested "Visual 
illusion induced by sound" by Ladan Shamsa, Yukiyasu Kamitanib, Shinsuke 

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