Two timing questions
I am running an eye-tracking experiment through opensesame and concerned about the accuracy of my RT measurements. I have two concerns that I'm wondering if the devs could help with:
1) I seem to be stuck with the legacy backend- the psycho back end crashes when I launch the calibration, and the Expyriment back-end timing seems very bad on my system- the experiment stalls for around half a second after I make each response. In contrast the pygame timing 'looks' good in that everything in the experiment happens instantly
From what I have read in Mathot et al., (2012) the pygame backends introduces about 20ms of imprecision in timing. I am wondering, does this 20ms kick over to response time measurements? I don't care so much if there is a little bit of variation in stimulus onset per se, but I do care if that variability leads to bad measurement of the time between stimulus presentation and the recorded response. That is, say the stimulus presentation was off by 10ms (due to lack of the vsync thing that the other back-ends have), but the response timer somehow knew that and adjusted for that, I'd be totally fine.
2) Currently I am logging RT by using time.time() at the start of a trial and after the eye movement response comes in. Is there a more precise method? Perhaps one that accounts for stimulus onset variability as described in (1).
Relatedly it seems that time.time() and clock.get_time() are somehow not that reliable on my system. I found that the eyetracker.wait_for_saccade_start() function from pygaze would crash because sometimes there would be no different in time between two valid samples (with a 500hz SMI eyetracker) leading to a division by zero on the velocity calc. I tried both the clock.get_time() function in pygaze and also swapping it out for time.time() and got the same result. Wondering could this be due to imprecision in the time.time() or clock.get_time() functions themselves?