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Stimulus presentation error

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  • Stimulus presentation error


    My program contains a trial with the following events:

    Event 1: Text, correct response is space bar
    Event 2: Movie, no response can be made
    Event 3: Text, correct response is string


    Everything proceeds as planned , except event 1 flashes on the screen for a second just prior to event 3. Any ideas on what is causing this?

    • In "Participant Input," I made sure to indicate that single-key responses are accepted only by events looking for single key responses (and string responses only by events looking for string responses).
    • Events 1 and 3 are set to "end the event and move to the next one" only after receiving a correct response. Event 2 is sent to end immediately after the movie finishes playing.
    • There are no stimulus lists involved.
    • All events are set to erase the screen before proceeding.
    • The trial is NOT set to randomize the events.


  • #2
    Hi Lisa,

    It's hard to tell without seeing the experiment, but I don't believe that the movie event type provides an option to erase the screen before playing the movie, which means that event 1 will stay on the screen until event 3 is presented.

    Does this seem like your problem?



    • #3
      Movies don't have the option to erase the screen.

      On OS X, the canvas that pictures and text are drawn onto is completely independent of how movies are drawn. A movie playing on the screen does not affect what was already there. This is why Event 1 is "flashing" on the screen. To get rid of this effect, tell Event 1 to erase the stimulus at the end of the event. This is a new feature as of 4.0.3, and it's in the picture/text settings dialog under the Presentation Options tab. This will erase Event 1 at the end of Event 1, so it won't be visible anymore when Event 3 comes up.

      I hope this helps!


      • #4
        how to erase movie after it ends


        I think I have a similar problem. The structure of my trials is as follows:

        1) Fixation cross
        2) Movie 1 (300ms; allow to play until end but allows other events to continue before the end of the movie, because I present an external stimulus during the movie)
        3) Mask (visual white noise, 500ms; allow to play until end, does not look for input until end of event)
        4) Movie 2 OR static image (300ms; wait for any response from participant before ending)

        This seems to works fine if the 4th event listed is a movie (although not on every computer I have run it on). However, if it is a picture file, it does not display. If I change the location or the size of the picture file, it is clear that the image does display, but it is hidden behind a white square left by the movie file. Is there a way to erase the movie stimulus completely once it has finished playing? Assuming that is the problem.

        Many thanks.


        • #5
          Please let me know if the workarounds that we discussed over the phone do not help.