[solved] RT measurement with stimulus->mask sketchpads

rhettclayton

Hi all,

I have a question about a flanker task I am trying to set up in OpenSesame.

I have four sequences; two shortened trials and two experimental trials. When I have been demo'ing the data output, I get an average ms response time that is ~300ms quicker than prior studies into the same area. Which makes me wonder about input lag.

However I found the ms response lag/confound articles confusing and not completely relevant to me.

The sequence (which is within a loop) runs through a fixation cross sketchpad, to a stimulus sketchpad, to a blank masking sketchad, to the keyboard logger, and the linked sound logger, then to the output logger.

I couldn't make sense enough of the RT time confound articles to understand whether my sequence is going to confound my RT measurements. The parallel function I attempted, but did not work under windows, nor OS X from my reckoning.

I am not sure, based on current arrangement, where the logger starts measuring RT from, how I can change this, and if there is a potential confound.

Here is my project so far http://www.filedropper.com/newexperiment

Please note the first trial run (Tr_Obj) is the trial that is the most up-to-date with my learnings of OpenSesame and I refer to this.

And here is a screenshot of the looped sequence

https://www.dropbox.com/s/dib5qlhlcw8g6g0/Screenshot 2016-02-27 14.58.55.png?dl=0

Eager for any input you may have.

Thanks!

rhettclayton

Edit: I may have worked out a workaround. The fixation cross goes up for two seconds. The stimuli for 300ms, and the response screen, being the final screen, goes up for 1 ms. Then the keyboard logger, I presume, runs from the last object, so if I want to measure from stimulus presentation to the time a participant kits a key, it would be 300ms + 1ms + [whatever ms response time OpenSesame logs].

Josh

Hi,

Indeed, the response time indicates the time from the moment your keyboard item started. If you want participants to be able to respond during the stimulus presentation time, however, this is problematic, (participants can only respond after the 300ms stimulus time).

If you want to change this, you can set the stimulus sketchpad to 0 ms, and set a new keyboard response item right after that with a timeout of 300 ms. Now you only want the response screen and subsequent (2nd) keyboard item to be used if participants didn't respond during those first 300 ms. To do this, click on your sequence item to reveal a list of run-if statements. For the response sketchpad and second keyboard item, you can enter the run-if statement keyboard_response = None

Now, you just need to add 300 ms to your response time if the second keyboard item is run. You can add an inline_script after the keyboard item, with the same run-if statement, and in the run phase of this inline script add the following line of code:

  exp.keyboard_response += 300

Cheers,

Josh

rhettclayton

Hey Josh,

To get your recommendation working, I had to set the run-if of response_time to 295, and the inline script to response_time += 300, however as it runs after the secondary keyboard logger, the script will only run if the participants' RT is exactly 295. How can I get around this? I tried to run the entire secondary process within a sequence, but that also error-ed out?

Also when trying to run the script to add 300 to the response_time variable just on it's own, to test it, 300ms is never added to the score. I am using exp.response_time += 300

Thanks a lot for your help,

Rhett

rhettclayton

Hey Josh (or others)

Please mark this as problem solved

Thanks a lot!

Rhett