Randomizing Trials and events within trials


I’m trying to program the following experiment and having a bit of difficulty:

The participants for the experiment are to be split into 3 groups, each group will be presented with the same set of 21 images in a random order but as follows:

Group 1 will see images 1 -7 (Set A) 3 times each, images 8 - 14 (Set B) 6 times each and images 15-21 (set C) 9 times each.

Group 2 - Set A 6 times each, Set B, 9 times each, Set C 3 times each

Group 3 - Set A 9 times each, Set B 3 times each, Set C 6 times each.

(Note, images will not be repeated 3, 6 or 9 times stright after each other - that also needs to form part of the randomization).

I know that I can put each stimulus in 3, 6 or 9 times and then set up randomization at trial lvel and that this will give me the result I want - however, I want to use a more elegant solution that randomizes the trials and then the events and allows for the repeats to be done at trial level and for the repeats to be selected according to whiich group the participant is in - currently no matter what I put in the Condition Experiment box in the trial editor I can not get the trials to run through more than once each!

I’m enclosing the experiment (without stimuli) so that you can see the structure and offer advice if possible!

369repeats_exp_v3_01.sl4 (9.56 KB)

Thank you for posting your experiment. Some modifications have been made and posted below.

Three Participant Groups were created, “Group 1,” “Group 2” and “Group 3.” Please note, when using Participant Groups the participant must select their designated group at run-time. See screen snapshots below.

Instead of having one block named “Trials,” three blocks were created in its place (one block for each group). Nine trials were also added to replace “Repeat_3,” “Repeat_6” and “Repeat_ 9.”

Within the Trial Editor, a Condition Expression was created to tell SuperLab how many times to present each trial.

Also, the experiment is no longer randomized by the events in the trial, but randomized by the trials in the block.

369repeats_exp_v3_01 B.zip (2.8 KB)

Hi Monica - thanks for that - I had managed to do things a slightly different way (which I will document and post when I’m at work tommorrow). I used groups to pick out the blocks to run so it’s helpfult ot know that’s how you would have done it too!




I have run the version you sent me - after putting it in the correct folder and linking the images back to it - however, as you can see from the attached data output text file (imported into Excel and sorted in the attached Excel file) each trial is repeated only once, regardless of what is stated in the Conditin Expression box - this is the problem I was having with the Condition Expression not working in the earlier version I programmed - I am using Slab 4.0.7b on Windows XP PC. I note you are using the mac version of Superlab and wonder if the none working of the Condition Expression function is a PC specific issue?

I did manage to program the expression as the student required by putting each trial in the required number of times (see pic in zip file) and using the groups function to determine which blocks to run…

Superlab file 369 repeats test.zip (32.9 KB)

I have your experiment, but I don’t have any of the files. Do you think you can post them? This problem should not be a cross platform issue.

Sorry not to get back to you sooner - have been off work sick. Can I send you an experiment package? Will that encapsulate al the files needed or do I just need to zip everything? I aslo have some digital out to Biopac markers using an rb830 response pad - shall i include those events too?


Please find attached the zipped experiment with the images included and also a couple of text files showing that the images are not repeating. Please let me know if you need anything else.



369repeats_exp_v3_01 with images.zip (1.27 MB)

There was one step I forgot to mention, I apologize. You will need to create a Macro in the Block Editor. Under If True, select Repeat Current Block. Once you created the Macro and your back in the Block Editor, make sure to check the box next to “Repeat Block.” Then, under Run this Macro: select After all trials in the block have been presented.

Monika, many thanks for that - it seems to have done the trick!