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about the timing issue

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  • about the timing issue

    Hi, our lab uses psychopy (based on python) to present stimuli for ERP experiments. But we find delays between the trigger sent by psychopy and the actual stimulus event recorded by stimtracker. Does anybody have some idea on what is wrong and possible solution?
    The delay is as large as 30ms to 40ms...

  • #2
    When sending event codes from the computer it will suffer delays from the USB drivers and should only be used to send event codes. i.e only to describe the trial, but not to mark its precise onset. To get the precise onset I suggest taking advantage of the lightsensor and built in audio stamping.

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    • #3
      Hi, what we found is that sending event codes from the computer is faster than the onset marked by lightsensor.

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      • #4
        The light sensors are really fast at detecting light (50 microseconds), though their release time is much slower (4 milliseconds). See the Specifications page. You will experience the longer 4 millisecond delay if you are switching from white to black.

        Sending event codes from the computer using USB will introduce variability.

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