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Show random images only once in block sequence


So I'm creating an experiment with two parts on a tablet.

Part 1 and 2: Four images of children are shown on screen four times and the participant rank the pictures 1-4 every screen, there are 16 pictures in total.

1 2 3 4

5 6 7 8

9 10 11 12

13 14 15 16

These images are drawn from a randomised factorial design with 3000+ rows as the images have conditions to them, for example only show two girls and two boys, don't show the same picture in the same sequence etc. I'm calling the pictures at random to location A, B, C and D.

My issue is that I want each picture to only be shown once in each part but preferably at a random location. I.e. if a picture has been used in one four-picture sequence do not use it again in that part as I want my participants to see every picture just once in each part (so twice in total). How would I go about this?

Any help would be much appreciated!



  • Hi Julia,

    I recommend using pen and paper and pseudocoding the conditioning you need for this experiment. It is not very complex, but wrapping your mind around it can be a little tricky. Also, I would separate the randomizing of the position from the randomizing of the images. Once, you have figured it out you can implement it in an inline_script by selecting random images from a list if they fulfill all requirements, and then assign them to possible locations.

    Does that make sense?

    Good luck,


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