Hi all, I just wanted to report a trick that fixed the timing for me. So now I’ve upgraded to Mac OS 26.5 beta. I don’t know if this works on previous versions or not. I tested this using Octave 11.1 and PTB 3.0.22. My initial test of this OS confirmed the VSync error, such that the effective frame rate was effectively halved. But when I changed my monitor refresh rate to 59.94 Hz, the problem went away. And it’s still fine when I switched it back to 60 Hz. Something about changing the system video refresh rate seems to have at least temporarily fixed the problem for me. I haven’t done any testing to see how stable it is. VBLSyncTest reports 1 out of 600 stimulus presentation deadlines missed, as it should.
The computer is a Mac Studio with M2 Ultra chip and Pro Display XDR.
I wanted to try this on my laptop, but my MacBook Air (M4) does not allow changes to the refresh rate; the frame-skipping error was initially still present with OS 26.5 beta.
HOWEVER, starting in the 1710 x 1107 (Default) spatial resolution, I get the frame skipping error. But when I switch to a higher (1920 x 1243) or lower (1440 x 932) resolution, the error goes away and VSync works fine. At first when I switched back to the default resolution, the VSync error returned, but the second time I switched resolutions and back (I may be a bit fuzzy on the details here), the Vsync error is also fixed at the default resolution…
How odd.
I don’t know what combination of OS, Octave, PTB fixed it, but the problem is *almost* resolved.
Presumably once the Vsync error goes away, it will stay fixed until you reboot, and then you just have to switch spatial or temporal resolutions upon restart to fix it.
Keith
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Keith Schneider
Professor, Department of Psychological & Brain Sciences
University of Delaware