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IsabelV

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Posts: 21
Reply with quote  #1 
Hi Jaewon.
I just noticed that when I run one of my tasks, the frame interval (shown in the lower left corner of the ML 2 interface) varies for some of the trials. For instance, for most trials it is 6.9ms, but for a few trials it some times changes to 13.89ms. What does this mean?

Thank you very much.
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Jaewon

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Reply with quote  #2 
You must have a 144-Hz monitor. It means that there was a skipped frame. It displays the worst performance occurred during the last trial.
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IsabelV

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Posts: 21
Reply with quote  #3 
That's right, the monitor is set at 144Hz refresh rate.
Is there a way avoid these frame interval variations? In one of my tasks, this frame interval goes up to 20.83ms! I want to make sure that the scenes are presented without much lag.
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Jaewon

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Reply with quote  #4 
There is a limit in the amount of work that your computer can do within 6.9 ms, so you can't completely avoid frame skipping.

In many cases, this frame skipping is not critical, because it mostly occurs within the first few frames of a trial or during static image presentation.

You can decrease the refresh rate. You might not see them if the refresh rate was 60 Hz.

If frame skipping is critical in your experiment, you need to decide how to handle it. Your option is either to ignore the skipped frames or to present them again.

TrialRecord.DiscardSkippedFrame = true;  % by default, skipped frames are discarded.

You actually cannot use the whole 6.9 ms, because the video buffer has to be submitted before 6.9 ms is up. The bigger your screen resolution is, the earlier the submission time should be. By default, NIMH ML tries to submit the buffer earlier by 10% of the frame length. So you have just ~6.2 ms to analyze input and draw the screen.
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