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  • contingent stimulus positioning

    I'm sorry if this had been covered already but my question involves how to have the position of stimulus 2 determined by the position of stimulus 1.

    This is most similar to a Posner Attention Network task in which there is a central fixation, then a cue above or below the fixation, and then the target which is presented in the same location as that preceding cue (either above or below fixation). I could do this by just creating trials with this sequence hard-wired, but I think there's a way to do this with Trial Levels or Rules. I thought that I would be able to set a Trial Level of position (up or down), and then have both events (cue and target) in each trial abide by that rule which is randomly assigned before each trial. So far, in any combination of trial levels (particularly randomize levels before start of each trial) I still haven't had any luck.

    My question seems to have been asked before: http://community.cedrus.com/showthre...imuli+location

    The last response says that with Superlab 5 this should be possible but not clear how to do it.

    Thanks for any help.

  • #2
    Hello James, it’s great to hear from you. Sorry to have missed your phone earlier today, would have been great to catch up after 15+ years!

    The attached experiment shows how this can be done. The technique is this:
    • Create a parameter of type counter and give it a minimum and a maximum, e.g. 1 and 2

    • Create a rule that assigns a random value to this parameter

    • Have your position trial variable set to “Manual” selection

    • Have two more rules: one to manually select the top position if the parameter got assigned a value of 1, and the other to select the bottom position if it's a value of 2

    Attached Files

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    • #3
      Thanks Hisham. That worked well. Is there a way to apply the position rule only to a subset of trials? The paradigm calls for four different kinds of trials. No cue, central cue, double cue (above and below), and a predictive cue (above or below).

      Right now, the rule seems to be affecting the randomization of the trials, so that one set of trials is presented then the next set of trials (e.g., double cue, then central cue. . . )

      Also, is it the case that the coinflip parameter is truly random? Meaning that, however unlikely, a given subject could have all predictive cues presented either above or below the fixation, or that there would be an uneven distribution of cues above or below?

      Thanks again!

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      • #4
        Sorry for the confusion. The randomization issue was completely unrelated. I did not have the rule checked for all condition types so absent the presentation of an off-center predictive cue, the counter would not get ticked and the other trials would keep presenting to the top or the bottom. This is all worked out now. Thanks for your help.

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        • #5
          I’m glad it worked. Yes, you can apply the randomization to a subset – just enable the three rules on the trials that you do want to randomize.

          And yes, the “Assign random number” action assigns a truly random value to the coinflip parameter.

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