Randomization of stimulus sequence within participants.

Comments

• Fab

  November 2023

  Hi @amoupsou,

  Not sure I understand your description. "I want all possible combinations of stimuli to be presented in each run of the experiment. However, in each trial, I want OpenSesame to show the stimuli in random order". If you present each combination in a random order, you won't be presentng every combination...

  Are you trying to say that you want all possible of three stimuli among a fixed list of five presented to each participant, but that the order of these three stimuli should be random?

  Best,

  Fabrice.

  
• amoupsou

  November 2023

  Hi @Fab , thank you very much for taking the time.

  You got it right, it is exactly what I mean!
• Fab

  November 2023

  Hi @amoupsou,

  In that case, the solution is fairly simple:

  (1) Create a loop and populate it with all the sub-selection of 3 stimuli from your set of 5. One sub-selection of 3 stimuli per row.

  1. {1, 2, 3}
  2. {1, 2, 4}
  3. {1, 2, 5}
  4. {1, 3, 4}
  5. {1, 3, 5}
  6. {1, 4, 5}
  7. {2, 3, 4}
  8. {2, 3, 5}
  9. {2, 4, 5}
  10. {3, 4, 5}

  Set your loop to run the rows in a random order. Each stimulus should be in its own column (that you for example call "stim1, "stim2" stim3")

  (2) to ensure that the stimuli are presented within each trial in a random order, use the shuffle_horiz function in the script of the loop: https://osdoc.cogsci.nl/4.0/manual/structure/loop/#shuffle_horiz. IN the example I set above, you'd have to add the following to the loop's script:

  shuffle_horiz stim1 stim3

  This method will ensure that all combinations of 3 stmuli from your set of 5 is presented once, in a random order, and that the 3 elements inside each combination are presented randomly for each participant.

  Hope this helps,

  Fabrice.

  
• amoupsou

  November 2023

  Hi @Fab , thank you very much for taking the time.

  I designed the experimental loop with a loop item. After it, I have entered the sketchpad items that will present each stimulus. I wonder though, if I need to enter a script, should I enter it before the first sketchpad?

  Thank you very much for helping out!

  

  
  
• Fab

  November 2023

  Hi @amoupsou,

  It all depends what you want that script to achieve. But if you're talking about the loop's script, you need to access the loop's script, not adding a Python script object anywhere.

  To access the loop's script, simply go here:

  

  You'll then see the loop's script. Simply add your shuffle_horiz instruction there.

  Hope this helps,

  Fabrice.

  
• eduard

  November 2023 edited November 2023

  Hi,

  I wonder though, if I need to enter a script, should I enter it before the first sketchpad?

  Is this question independent of your previous question? The solution that @Fab described does not require an inline_script item. You have to directly write the combinations into the loop table (`experimental loop`) and add the shuffle_horiz to the script of the experimentalloop script. You can find it by clicking on the little icon with the two sliders in the top right corner:

  

  and select `view script` there. Once there, you can copy the command in there, and save it.

  Does this make sense?

  Eduard

  edit: Guess Fab was quicker ;)

  
• amoupsou

  November 2023

  @Fab @eduard thank you both very much, it worked!