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cbukach
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Join Date: Oct 2006
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Response Deadlines & Stimulus offsets., Posted October 3rd, 2006 #1
I would like to start collecting a response at the onset of a stimulus, and continue waiting for a response after the stimulus disappears. For example, I would like a picture to appear, start waiting for a response, have the picture disappear after 1000 ms, and continue waiting for a response for another 1000 ms while the screen is blank. How do I accomplish this and still have the correct response tied to the particular stimulus that is shown?

Thanks!
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Hank
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Posted October 3rd, 2006 #2
I haven't found a good way, but I have found a way.

The solution I've come up with involves two stimulus lists, code values, and correct responses based on code values.

Stimulus lists don't get randomized, and if you use more than one in the same trial, the items are pared up linearly. That is, list 1 item 1 gets paired with list 2 item 1. list 1 item 2 gets paired with list 2 item 2, and so on. If one list runs out of items, it loops back around to the beginning.

Your first stimulus list straight forward. You add your expected items to it and set the appropriate code values. Your second stimulus list is less obvious. This will be a text stim list with as many items as are in the first list. The content of the text is unimportant (as we will display it the same color as your background), but it is important that the code values match up with the items in your first stimulus list. I would take advantage of the unimportance of the text and make it meaningful. For example, put the name of the stimulus as the text value, or whatever helps you properly pair items in the two lists.

Next, we will create a trial with two events. The first event is your stimulus, which is pulled from the stimulus list. The correct response depends on the code value, and the event ends after your specified time of 1000ms. The second event is a text event, displaying text from our second stimulus list. The color of the text should match your background color, so that it appears we simply erased the screen. The correct response for this is also set to depend on a code value. It's important that you set up some sort of feedback to skip this second event in case the participant responds during the first event (assuming you want the trial to end on a response, that is).


This is a *very* brief overview of what I got to work--far from step-by-step directions. Maybe it will help... so far, it's the only solution I've come up with.
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Hisham
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Posted October 3rd, 2006 #3
You will need two events to accomplish this. The first event presents the picture and would have a 1000 ms time limit. In the Input tab of the Event Editor, make sure to turn on the "Reset RT Timer" checkbox.

The second event can be something like a Text event (with no text actually presented) for the sole purpose of erasing the screen and waiting for the response. It would also have a 1000 ms time limit but the "Reset RT timer" checkbox should not be turned on. This would insure that all measured RTs are relative to the onset of the stimulus. It would also have the same correct response settings as the first event.

One more thing: what if the participant responds during the first event? In this case, you don't want the 2nd event to be presented; usually you'd want to move on to the next trial The way to do this is to use feedbacks for the first event. To do so in the Event Editor:

1. Click on the Feedback tab

2. Click on the (+) button on the left hand side to specify a feedback condition. A small dialog will appear.

3. Select the condition that's appropriate for your experiment then click on OK. The conditions dialog will disappear and you will see a default "action" created on the right hand side.

4. If that action is not "Skip any remaining events", then double-click on it and change it to "Skip any remaining events".

This way, if the participant responds during the 1st event, SuperLab will skip the 2nd one and move on to the next trial. If the participant does not respond, SuperLab will move to the next event which erases the screen and gives the participant an additional 1000 ms to respond.

Let me know if you need additional help.
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cbukach
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Posted October 3rd, 2006 #4
OK, these are options I had considered, but thought there might be a simple "erase" screen function or stimulus setting of which I was not aware. It would be helpful in future editions to be able to erase the stimulus but still be waiting for a response without having to make a new event that was contingent on feedback and having the same response code as the previous event.
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Hisham
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Posted October 3rd, 2006 #5
No screen erase function yet.
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