.started and .stopped columns for stimuli presented for 1 frame?


I am trying to figure out if I can be sure that my stimuli is only presented for only 1 frame?
When looking at the .started and .stopped columns in my csv file, I see durations of typically around 21-28 ms. I am using a 60 Hz display, so frame times should theoretically be around 16.7 ms.
For a stimuli to be presented for only 1 frame, I would expect the calculated duration would need to be less than the time it takes to present 1 frame? Alternatively, if .started is immediately following a screen refresh the duration would presumably just need to be less than 2 screen refreshes, that is 33.4 ms.

The issue came up as I have been trying to record my screen with Fraps (a screen capture tool), and going through the video frame-by-frame I sometimes see the stimuli being presented for 2-3 frames, but there does not seem be any correlation to the calculated duration from the .started and .stopped data, to the trials when stimuli appeared to be presented for more than 1 frame. I am aware that recording does take up systems resources, so the recording itself might induce a delay that is not present without it, or Fraps might for whatever reason sometimes save several identical frames even if they don’t represent what was shown on the monitor. (I don’t need Fraps for my experiment, I just need to be sure that I know for how long my stimuli was presented on monitor)


try a photo diode and an oscilloscop to register the presentation duration. But registering just one frame might be difficult. In addition, presentation duration does not just depend on the refresh rate but also on the quality of the monitor and the color/brightness switch, although 60 Hz shouldn’t be too much of a problem (on a good monitor).

Best wishes Jens

Hi Jens

Thanks a lot for the suggestion, i might try that