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Thread: Randomization question

  1. #1

    Randomization question

    I am wondering if it is possible to have, say, 10 stimuli in a folder, but to have DirectRT programmed so that it will only present a random set of 5 of the 10 stimuli. If this is possible, I'm also wondering how it can be done.

  2. #2
    Join Date
    Mar 2009
    This is definitely possible. There's a few ways you could do this. The first method would be to use the rand() function.

    Using this function allows for the input file to be dynamically updated with one of the 10 stimuli before the file is presented to the user.


    Another method would be to use a random stimlist. More information on stimlists can be found here:

    A random stimlist would be able to randomly select 5 of the 10 stimuli. Take a look at the Samples folder, and try out one of the stimlist samples. The path to this folder is most likely as followed: "C:\DirectRT\Samples\1 - Bare Bones".

  3. #3
    Thank you very much for your help! I got it to randomize all my stimuli. One followup question, though: How do I make it record which stimuli it used for each trial? I have my participants being presented with stimuli at random and rating each stimuli, and I would need to know which image it flashed so that I can match up ratings with that image?


  4. #4
    Join Date
    Mar 2009
    Hm - within the data log files, this information should be displayed. In order to locate the log files produced by DirectRT simply locate the 'Data' folder within the same folder that your input file is located at. From within the 'Data' folder you will find the folder 'log'. This folder will contain .CSV log files created by each subject that took the experiment.

    Does this help?

  5. #5

    The way my screens are set up, they have two stimuli (one is an instruction asking them to rate the image, and the other is the image). I would like for the data file to contain both--which image and which rating question appeared on any given trial, but as of now it only tells me the rating question and not which image it randomly selected. To be more clear, there are about 90 images that get rated for 2 things "attractiveness" and "willingness to date," and so each image would have two different screens dedicated to it and it is the sum total of all these questions and images that i would like to have randomized.


  6. #6
    Join Date
    Mar 2009
    Hm, would it be possible to send over your input file?
    The stimuli being used would not be necessary.

    Let's see what could be going wrong.

  7. #7
    it's attached! thank you so much for your help!
    Attached Files Attached Files

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