Random presentation times?

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11-14-2007, 02:28 PM
jarvis24

Random presentation times?

[I][edited from support email][/I]
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.
11-14-2007, 02:30 PM
jarvis24

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:

[URL="http://www.empirisoft.com/directrt/help/directrt_using_random_values.htm"]www.empirisoft.com/directrt/help/directrt_using_random_values.htm[/URL]

Hope that helps!
09-23-2008, 09:41 AM
rjrydell

Random Sounds for Distraction

Hey Blair,

I read the page you mentioned above ... [URL]http://www.empirisoft.com/directrt/help/_helpcontents.htm?directrt_using_random_values.htm[/URL] ... 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
09-24-2008, 05:07 PM
jarvis24

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.