Randomly select from a list of stimuli but include breaks after a pre determined number of trials

[Heath Matheson]

Hi all,

I have an experiment in which I am showing 100 stimuli to participants and am recording object names. I would like to show 20 images, randomly selected from the 100, then have a break, then show another randomly selected 20 images, etc, until all 100 have been shown across 5 blocks with breaks in between them. 

My experiment looks like this:

SessionProc

---Instructions

---Blocklist (with one level)

-------Triallist (with a list of all 100 stimuli)

-------TrialProc

-------------Fixation

-------------SlidePicture

---End

So right now, I can show the 100 images randomly all the way through. I think to introduce breaks I need to play with nesting but everything I am doing doesn't work and seems overly complicated. The problem is easily solved if I don't worry about randomizing the presentation of all 100 stimuli but this is an important part of the experiment. 

Any suggestions for how to include periodic breaks? 

Thanks!

Heath 

[Heath Matheson]

Here is the solution, provided by friendly Alexandre Comte:

- In the Blocklist define 2 levels. The first one is for the TrialProc (weight=20) and the second one for the BreakProc (weight=1).

- In the properties of Blocklist, set the number of cycles at 5, with a sequential order. 

- TrialList: random order

- finally insert your break in the TrialProc

Heath

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Heath E Matheson PhD
Postdoctoral Fellow

Center for Cognitive Neuroscience

University of Pennsylvania 

3720 Walnut Street
Philadelphia, PA 

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[Heath Matheson]

Oh! And do make sure that, in the properties of the TrialList, under the Reset/Exit tab,  the 'Reset at beginning of each run" is unselected!

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[Theodore Teow]

Thanks for sharing this, Alexandre and Heath! I'm sure I'll find this useful in future.

Cheers,
Theodore Teow
PhD Candidate
Project KIDS Neurodevelopmental Research Centre
Murdoch University
90 South Street
Murdoch, Western Australia