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Is there a way to Standardize speed for DotStim?

Hi,

I am using a dotstim stimulus that was written in coder and was wondering if someone could explain how to standardize the speed setting for the dots? I.e. have the relative speed of the dots be the same regardless of the computer it is run on. I looked at the documentation which only says it is in units/frame but this doesn’t make sense to me.
I recently took the stimulus to run at another facility on their computer and the speed was significantly faster although nothing in the code was changed and both computers operate at a frame rate of 60, but they also have a computer that ran at twice that (but i didn’t get a chance to use it on that one).

So how would I go about coding my stimulus so that if I have it running at 0.1 speed on one computer it would adjust to be the same rate on another computer so that visibly they are running close to if not the same relative speed.

Thank you,
Tim

  • How did you ascertain that? Empirically, did the two data output files each contain 60 in the frame rate column?
  • Do you know that both experiments were set to use the same units? If you haven’t explicitly specified the units in your experiment settings or within the stimulus component itself, then it will run using the default units set in PsychoPy’s preferences (i.e. at the application level on that particular computer). That could certainly account for velocity differences, although they might often tend to spectacularly and obviously different (e.g. the difference between norm and pix units) but some might be close enough (cm vs deg) in certain set-ups that they might be relatively close.