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 :stuck_out_tongue: , except event 1 flashes on the screen for a second just prior to event 3. :eek: 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.


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?


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!

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.

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