Timing issue with PsychoJS

[rob-linguistics13]

Thank you for this, @jon, your explanation helped a lot. A few comments follow.

@jon

Note that some of the variability you’re measuring above is an artefact of the measurement. I’m assuming that you’re measuring this based on reported flip times, which has some variability too.

The measurements reported were calculated by calling the function clock.getTime() (and the PsychoJS counterpart) were used to measure the actual duration in second for each routine as described here. The same method was used to measure stimulus durations regardless of whether stimulus durations were set up in seconds or in flips. So, I am not sure the variability I am not sure the variability is an actual artifact of the measurement itself, unless I misread the way getTime() works.

@jon

Actually to complicate things a bit further you can also get what appears a shorter duration if the framebuffer is ‘synchronized’ but not ‘blocking’.

Can you expand on this? Is that an option on PsychoPy/PsychoJS?

@jon

Ultimately, to know whether your stimulus lasted the duration you expected, especially in a browser, you would need to use a photodiode and measurement hardware. I expect when you do that the precision will improve a little (the scatter around the peaks will dissappear and some of the flanking peaks will be reduced) but I do also expect you to see some dropped/gained frames when running in a browser.

I am no expert on any of this, so I wonder whether any of this can be set up for online experiments.

Thanks!