Inconsistent refresh rate on Apple M1 Max

Hello everyone,

We’re running an experiment using a priming paradigm with: 33ms primes (2 frames) and 500ms targets (30 frames) that should (supposedly) work with a 60Hz refresh rate.

However, after analysing the presentation duration of both primes and targets, we uncovered a major anomaly in the refresh rate values. Not only is the refresh rate different from 60Hz, but it also seems to vary from stimulus to stimulus.

We have a MacBook Pro 16-inch 2021, with an Apple M1 Max chip with 32 cores
We’re using PsychoPy version 2022.2.5
We already set the refresh rate in the Mac to 60Hz in System Settings > Displays > Refresh rate

Here are two elements to illustrate the refresh rate anomaly:

(1) Example of a log file from PsychoPy. It is interesting to note the pattern of dropped frames isn’t at all consistent among the participants (+/- 30): sometimes we only have two dropped frames, sometimes the right refresh rate is 60Hz, and sometimes the refresh rate is impossible to calculate.

122.5314 WARNING t of last frame was 24.50ms (=1/40)
122.5940 WARNING t of last frame was 21.16ms (=1/47)
122.8491 WARNING t of last frame was 25.81ms (=1/38)
122.8781 WARNING t of last frame was 22.74ms (=1/43)
122.9772 WARNING Multiple dropped frames have occurred - I’ll stop bothering you about them!
123.1368 WARNING Couldn’t measure a consistent frame rate!

  • Is your graphics card set to sync to vertical blank?
  • Are you running other processes on your computer?

(2) Example of the variable refresh rate for the (100) primes presented to a participant:

Has anyone encountered this problem before? Any help is greatly appreciated.
Thanks a lot,