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[open] Dot-Prob task

edited December 2012 in OpenSesame

I need help to setup a dot-prob task. Specifically, I am not sure how to add a dot to appear for 500 ms either on the left or the right of the fixation point that subtends to one of the words that was appeared at the left or the right of the fixation point in the earlier trial.
If I could see a sample program for this, that will be perfect.



  • edited 10:15AM

    Hi Masoud,

    If I understand correctly, your trial sequence should be as follows:

    • Firstly, you have a sketchpad that contains a fixation dot and a pair of words, one presented to the right and one presented to the left.
    • Next, you have second sketchpad containing the fixation dot and a probe. The probe is a dot that appears either at the left or the right of fixation (so, at the same location as one of the two previously-presented words).

    I think the best way to obtain this is to define the location (or, more specifically, the x coordinate) of the probe (in pixels, relative to 0, the center) in a loop item. By doing so, you can simply edit the script of the second sketchpad item a little bit in order to present the probe at the desired location. For example, change:

    draw circle 250 0 10 fill=1 penwidth=1 color=white show_if="always"

    draw circle [probe_position] 0 10 fill=1 penwidth=1 color=white show_if="always"

    I uploaded a simple example experiment here, which will hopefully get you started (simply download and "save as" with the extension ".opensesame"):

    You could also take a look at the following two links:

    For a clear demonstration of how to use variables defined in a loop item in sketchpad item script, see the step-by-step tutorial, especially "Step 6: Draw the sketchpad items":

    For more info about defining variables, see also:

    Hope this helps!



  • edited January 2013

    Dear Lotje,
    Thanks very much. Will try .


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