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Thread: problem with between block randomization when using the "display former stim" func

  1. #1
    Join Date
    Nov 2005

    problem with between block randomization when using the "display former stim" func


    I am using the 2008 version. I need to re display a stimulus for a participant for her/him to judge whether it is familiar or not. between the judgements she performs a second distractor task (achieved trough a composite screen, i.e. within the same row/trail). As i need the probe and the intial stim to follow one another AND i would like to randomize all the trails of the experiment a bright student that i worked with thought of :a. giving the pair of stimuli the same block number and a different trial number b. randomizing the different trials using BGW randomization. should have worked but for some reason dRT does not randomize the blocks (as shows the log file) and just presents them sequentially. just to clarify, i have now say 20 no probe blocks "blocks" each consisting of a single trial, an additional 5 "blocks" (probe trials) each consists of two trials sharing the same block number.

  2. #2
    Join Date
    Nov 2005

    Further localization of the problem: BGR doesn't work for some reason

    Hiya. I'm attaching a simplfied data file. Apparently it wasn't my fancy stuff that killed BGR as even this version doesn't randomize. Ideas?

    Attached Files Attached Files

  3. #3
    Join Date
    Mar 2009
    I've re-attached a copy of your experiment file. It would seem that you may be using the BGW (BGR) values incorrectly. When trials are assigned a specific BGR, this value acts as an identity to a group. For instance, let's suppose the following is true about an experiment:
    - Trials 1 and 2 have a BGR value of 1.
    - Trials 3 and 4 have a BGR value of 2.
    - Trials 5 and 6 have a BGR value of 3.
    - Trials 7 and 8 have a BGR value of 4.
    In the given scenario, each group of trials would stay together - trials 1 and 2, 3 and 4, 5 and 6, and 7 and 8 will never be separated from each other - as long as they have the same BGR value. With these values we're telling the software that we want each of these four groups to be randomized among each other. For instance, given the above, you may now have the following order after the experiment has executed:
    - Trial 3 and 4.
    - Trial 7 and 8.
    - Trial 1 and 2.
    - Trial 5 and 6.
    Each of the four groups are now simply randomized among each other; however the contents of each group remains the same. I believe that this demonstration is most likely very close to what you're trying to achieve. Setting the Block value and the Trial values as you've done will not allow for the randomization to take place. Allocating a value of "1" for each trial's BGR column can also cause for the randomization to not work correctly - as you're specifying that you want this group randomized among no other groups, which means that it will simply run through the experiment as if no BGR value was assigned at all. Does this make sense? If you do not want items randomized, set the value to '0'.

    For more information on the randomization techniques DirectRT has to offer, see the following links:
    BGR - http://www.empirisoft.com/directrt/h...een_groups.htm
    WGR - http://www.empirisoft.com/directrt/h...hin_groups.htm
    rand() - http://www.empirisoft.com/directrt/h...dom_values.htm

    You may also want to see the samples folder 'Ordering Trials' (3) for examples on how these functions are used.
    Attached Files Attached Files

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