I’m trying to present the same set of words (from a stimulus list) several times over, in random order each time, at increasing display times for each repeat of the set. In other words, a participant should see every word in the list at 20ms, then the same list again at 40ms, etc. The task involves making a judgement about the word on a subsequent masked event so that each trial is structured:
fixation
display word
response
My initial approach has been to use a trial variable (which I’ve called “display duration”) that specifies my display time values, and make the level selection sequential. I then end the display word event after a variable time limit, taking the times from the display duration variable.
My problem is that I can’t figure out what I should specify in the “Restart sequence before start of…” option in the trial variable settings. I want it to run through the same sequence of values once per participant, but if I restart sequence by experiment (or block), then each successive word uses a new display time as it continuously cycles through the display values. If I restart sequence by trial, then each repeat of the word set is shown at the first display value (shortest time).
I’ve also tried creating duplicate trials and/or blocks to try to trigger the sequence I want, but no success.
Is what I’m attempting possible using a trial variable? Or will I have to expand the stimulus list into multiple events and set the display times separately?
Trial variables aren’t the correct approach to this, from what it sounds like you’re trying to do. You said you want increasing display times. Are you wanting them to increase arbitrarily, or do you want them to increase up to a certain point?
In order to do what you want, you’ll need to create a block for each display time that you want to use. In this block will be one trial. In this trial, you have the three events you listed.
The second event (display word) will be different for each block, and you’ll have to manually set the times that you want to use. Each of these will use the same stimulus list as the source.
It seems like the correct response at the third event will depend on what word was actually presented during the second event, so the best approach here will probably be to also use the stimulus list, but to present the stimulus offscreen so the participant doesn’t see it. We can then set the correct response based on the stimulus that was presented. Note that when you use a stimulus list more than once in the same trial, the same stimulus is used.
If you’re wanting to stop increasing the times at a certain point, things get more complicated, and we’ll begin using Macros.
Thanks Hank - once I abandoned attempts to use trial variables, I got it working with your suggestion of separate blocks, trials and events for each level of display time. Macros aren’t necessary
Hi there,
I am wondering whether it is possible to do something similar; that is, have a set of trials for PArticipant, with random order A, that is then presented in the identical order for a subsequent block of trials (in which the task differs); but with a new random order for each subject?
You can randomize under the block level and choose the option Once per group of participants. If you want your groups to have a different randomization order, then make separate Participant Groups, which is found under the Experiment menu. Then, when you go to run the experiment you would choose the participant group you want when the Run Experiment window comes up.
