Randomizing Trials Within A Block


I am creating an experiment in which participants will be presented with the following events:

Fixation Cross for 500ms

Pictures from a stimulus list for 250ms

A Cue from a stimulus list for 100ms

An ISI of 5000ms

A Response Box

A Rating screen

Repeat for the 24 pictures in the list

Then I am repeat the same grouping but with pictures from a different stimulus list and cues from a different stimulus.

I cannot however find a way to randomize the trials within this block so that I have have, for example, 2 pictures from stimulus set 1 with cues from set 1 followed by 4 images from stimulus set 2 and cues from set 2.

Is there any way to go about doing this?

I’ve created and attached an experiment that randomly alternates between two trials, each with their own events and stimulus lists.

The key is to use the “Collection of Trials” parameter and list item tags:

  • give each list item a unique tag value.

  • make sure to add each presented trial to the collection via event feedback.

  • only present trials if they are not already contained in the collection.

There are other subtleties such as repeating the block via trial rules rather than block options, but those are mentioned in the experiment notes.

alternatingTrials.sl5 (6.47 KB)

Randomizng Trials Within a Block


Firstly thank you for taking the time to create that sample experiment. I have yet to use parameters or rules so I am happy you showed me how to do that!

I am still unable to get the experiment to randomize across the trials however.

Right now I have:

12 neutral images that correspond to 12 cues
12 negative images that correspond to 12 different cues

But when I set all the options and rules and lists I do not get a randomization rather I get it sequentially.

I have attached the experiment package if you maybe have some time to help.

For the purpose of this I have only linked the events that present the image and the event that presents a cue.

Thank you!

  • David

EDATrials 1.0.zip (1.88 MB)

I see that you are only randomizing your block once per experiment run. This must be set to every time the block is presented in order to get the randomly alternating trials.

Change this and let me know if the experiment works how you wish.



You are a life saver! I never knew about this functionality before and as far as I can see the script is working as intended. Thank you so much!

  • David