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Thread: Random presentation times?

  1. #1
    Join Date
    Nov 2005
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    3,323

    Random presentation times?

    [edited from support email]
    I'm getting ready to order the ML and DRT 2008 upgrades for my lab, but I had one quick question about DRT. Can you set the stimulus presentation times to be randomly determined? That is, can I ask for a certain image to be displayed either at any point from say 200ms-500ms, or for a specific duration time to be randomly selected from a list of possible display duration times? The reason I ask is that we want to do a version of Josh Correll's shooter bias studies.

  2. #2
    Join Date
    Nov 2005
    Posts
    3,323
    Yes, you can generate any value in the input file as a true random number from within a specified range, or you can have the value randomly selected from a set. For details, see:

    www.empirisoft.com/directrt/help/directrt_using_random_values.htm

    Hope that helps!

  3. #3
    Join Date
    Aug 2008
    Posts
    1

    Random Sounds for Distraction

    Hey Blair,

    I read the page you mentioned above ... http://www.empirisoft.com/directrt/h...dom_values.htm ... and I was wondering how I could randomly present a sound while participants are reading a sentence - the purpose of the sound would be to distract them. I would want the occurrance of the sound to be random (so participants cannot predict it) and the sound, but not the sentence, would be turned off by a keypress (the sentence would be turned off by a pre-set time or a different keypress). This would be similar to a Petty et al. (1976) distraction task. Any thoughts or any posts on this issue?

    Best,

    BJ

  4. #4
    Join Date
    Nov 2005
    Posts
    3,323
    Playing a random sound during another stimuli is not a problem. I would probably just randomly select it from a stim file. Have an embedded silence in the sound file to create an onset and then, without delay, present the sentence. Then take two RTs to the sentence--one for the sound and a second one for the sentence itself--using separate valid keys for each. There may be other ways, but that's off the top of my head. You can also do a search on here for "probe" -- you might find some useful links with that--both for DirectRT and MediaLab.

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