Randomized Event Presentations/Overlapping Stimuli


I am setting up an experiment with a breakdown of

Instructions-presented until participant input
Trial 1 attached to events “blank screen” and “fixation cross”
Trial 2 attached to events “blank screen,” “fixation cross,” and a stimulus list.

The first problem I have is randomizing the stimulus list (a series of 60 faces) without randomizing the fixation cross/blank screen occuring in between each face presenation. Sometimes it seems I’ve fiddled it to the point of success but a consistant problem is a flicker of the fixation cross on it’s first presentation.

The second problem I am having is programming a random assignment of a color patch onto the photo but NOT on the face. Is there a way to specify parameters for random presentation? The faces should randomize once per participant but the location of the color patches can randomize more often. If not, it is possible for me to manually “randomize” the color patch presentation and upload it as .bmp into superlab. In that case, how do I present to each participant a face 1 + color patch without having that same face present itself again with a different color patch assigment?
Do they all have to be seperate events? Seperate trials?

Thankyou so much for your time.


Randomizing trials should be easy. Keeping the fixation cross and blank screen in the same order is not a problem as long as randomization is done at the block level (in the Block Editor’s Randomize tab). A flicker issue would be unrelated to randomization and is probably due to an event erasing the screen or something like that.

You can randomize the presentation of a color patch by taking advantage of trial variables. They let you create any number of levels/positions on the screen, and even off-screen positions. Do you need to randomize the color of the patch itself as well?



I’ve been putting the color patches onto the faces in a different program, not knowing how to randomize color patches onto the face in a number of specified locations. There are three colors for the color patches and 10 locations on the images where I would like them to randomly appear. Is this all possible within superlab??

It depends. SuperLab provides trial variables that will let you vary the color, the location, or both. If you can specify locations on the screen so that the patches appear on the faces correctly and you can create the patch as an event of type Text, then you can do it and vary the color as well. Much depends on the photos of the faces.

For displaying a patch, I suggest that you create the patch as an event of type Text and use a symbols font such as Wingdings or Symbol. You will probably find something that looks close enough to a patch.

To create trial variables, click on the Experiment menu and then click on Trial Variables.

To use trial variables, while editing an event click on the Stimulus tab then on the Settings button. A Text Settings dialog will appear:

  • Click on the [B]Position[/B] then click on the popup menu to change the position from [B]Fixed at location[/B] to [B]Variable[/B].
  • Click on the [B]Text Color[/B] tab then click on the popup menu to change the font color from [B]Fixed[/B] to [B]Variable[/B].
I hope this helps,