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Thread: Unwanted delay between stimulus and mask

  1. #1
    Join Date
    Nov 2005
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    3,320

    Unwanted delay between stimulus and mask

    [edited from support email]

    I am using DirectRT to present faces for 12ms, which is working fantastically. Immediately following the face I need to put a backward mask. It seems, however, that there is load time in between the face and the mask (as much as 120ms). This seems to be allowing for an after-image. Vision experts in my department have informed me that this would mean that I cannot claim my stimulus is being presented for only 12ms.

    I wanted to make you aware of this problem (I suspect you have encountered this and have a solution) and also to inquire whether there is a way to pre-load everything so that there is no interval time in between (naturally, i have set the inter-trial interval to zero in the styles' options--my goal is to actually make this zero).

    Note: We are not intending to do subliminal presentation, necessarily. We can make the image "invisible" by using both a forward and backward mask. We would prefer it to be supraliminally presented at 12ms.

    I await your response with GREAT anticipation..
    Last edited by jarvis24; 09-14-2006 at 02:40 PM.

  2. #2
    Join Date
    Nov 2005
    Posts
    3,320
    Do you have the face and subsequent mask on the same or separate lines in your input file?

    Separate lines. I know we had problems before with presentations timing out correctly when they were on the same line but that's probably a hardware limitation.
    They really need to be part of the same trial. DirectRT uses the trial interval to prepare the next trial--i.e., the next line in your input file. That will typically be the value set in Options of your style file. By default it's usually 1000ms, so I'm guessing you've already tried setting it to 0ms? Check out the section on trial intervals in the users guide to see why that's usually not a good idea.

    However, if you display your image for 12ms and then have a subsequent mask for 100ms (or whatever) you should see no delay (i.e., 0ms) between the two. If you experience trouble with the display timing when you do it this way, send me a copy of your input and style files and I'll take a look at them.

    -Blair
    Last edited by jarvis24; 09-14-2006 at 03:30 PM.

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