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Tachistoscopic presentation of visual stimuli using superlab

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  • Tachistoscopic presentation of visual stimuli using superlab

    I have been able to use a licenced copy of superlab on my institution and I was trying to present visual stimuli jpeg and bmp images for 100ms interval.

    The problem is that stimuli are presented with distorted edges initially and then the image clears. Imagine for instance when you navigate on the internet to see a picture that progressivelly loads. First is unclear and blurry and as the explorer downloads the image, the image becomes clearer and clearer.

    This is what I experienced today when I was preparing a tachistoscopic experiment (an experiment where stimuli have to be presented for brief intervals).

    For that kind of experiments the experimenter wants to have clear image. Coupled with the problem of monitor refresh rate, the way superlab behaves is not helpful.

    The monitor I used was an LCD monitor with 60hz refresh rate and this happens for both jpeg and bmp files. I wouldnt think that this could be a problem with the processor which is a relativelly good pentium 4, or memory.

    Could it be that it is a hardware problem? Could it be that another piece of microsoft or other software interacts with superlab and generates this problem? Or there is something I can do in superlab to fix the problem?

    I tried clearing the screen before presenting stimuli, loading all trials to memory before initiating the experiment, I have tested the buffer setting etc (unfortunatelly I do not have superlab on my home PC to use the exact terms).

    So, do you have any advice can I do anything?

  • #2
    LCD Smearing?

    Could it be smearing/ghosting by the monitor? If you have a CRT monitor with the same refresh rate, you might give it a try to see if it helps. You could also try a different LCD monitor. Here's a reference to LCD smearing in the context of commercial LCD video: http://www.lcdtvbuyingguide.com/lcdt...onsetime.shtml

    Greg Shenaut

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    • #3
      It could be. If this is the case then I may not have serious problems doing something about it. However what in notice is that only the edges of objects are affected by that. For instance, if I present a square its edges will be distorted for brief periods and then cleared. However the area (the internal colour of the square) seems to be ok from the presentation onset. This is what I find strange. Do you think that this could be caused by smearing/ghosting? Because in that case the whole square and not just the edges would be problematic.

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      • #4
        Video test experiment?

        Well, if it were me, I'd try things like changing colors, changing size, changing shape, and changing location to see if you get the effect everywhere on the display. Also, comparing the effect on a different display might be interesting.

        You might pop an action-oriented movie DVD into the PC and look at it on that display, to see if you get any distortion/fuzz/smearing whatever.

        Actually, an interesting utility for the lab would be a SuperLab-based video test program qua "experiment" that would put up a set of extreme sequences of objects, movements, colors, etc., in order to verify how well a certain display will work as a t-scope style display. The same program/experiment could create a logfile that could be analyzed to figure out various essential timing parameters of the machine and the display for use in setting up real experiments.

        Greg Shenaut

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        • #5
          I concur with Greg. That's probably a better answer than I could have come up with.

          I would be very surprised to find this to be a SuperLab problem, considering the way this portion of the program is organized. Also, this shouldn't be affected by other software.

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          • #6
            Indeed it was not a superlab problem. Today I used a cathode display and worked fine. Sorry for the false alert.

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            • #7
              Visual Field Presentation Studies

              Hi Folks,

              Just found a few posts from 2007 on T-scope work with SuperLab. I am wondering if anyone can advise me regarding standard specifications for using picture files (let's say with a word) such that they appear selectively to the right hemisphere (Left Visual Field) or the left hemisphere (Right Visual Field). And also, how long to display the word on the screen for this kind of task? If anyone has a template to use that has been successful this would be much appreciated.

              Thank you,
              Kathleen

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