Amrita,
During any trial, there is a period before the stimulus appears during
which a response could be made, which you might call the 'waiting
period' or inter-trial interval (ITI). The delay variable in the data
file indicates the programmed time between when the trial actually
started and _either_ a stimulus was presented, or a response was made.
The variable delay2 indicates the actual measured delay, which is
usually a few ms longer than programmed, because timing is going to be
synched to the refresh cycle. Notice that on the first line you
examined, the delay2 is shorter than delay, which means they made an
(incorrect) anticipatory response--before the stimulus was presented.
An x is put into resp1 when this is done. The task is designed so that
the subject does not know their early responses are being recorded, but
this is how you can tell. It will only record the first early
response--if they jam the x key multiple times, you won't know it.
Note that the trial cannot proceed until they make an actual response
after the stimulus appears, so there will always be a response in column
resp2. In theory, you could modify the task to have a timeout, but I
never incorporated that logic. The 550 on the first line still
indicates the time from the onset of the x until the response key was
pressed, so it is a valid response time. But because they made an
anticipatory response on that trial, you may want to discard it during
analysis.
If you look at the final report (see example below), the information
about resp1 is not used. That is, the 'anticipations' just code those
trials whose response is < 150 ms, whether or not they made a response
during the waiting period.
Hope this help,
Shane
------------------------------------------------------
Report for PEBL Simple Response Time Task Version 0.2
PEBL Version 2.1
Started at: Tue Oct 15 15:58:02 2019
Finished at: Tue Oct 15 15:59:29 2019
http://pebl.sf.net
Participant Code: 20
Stimulus:X
------------------------------------------------------
Statistic Value
------------------------------------------------------
Number of blocks 2
Trials per blocks 25
Stimulus X
Total Trials 25
Anticipations (<150) 2
Delayed Responses (>3000) 0
Correct RT Mean 343.521
Correct RT Median 301
Correct RT Min 252
Correct RT Max 847
Correct RT SD 121.811
Delay N Mean Std. Dev
--------------------------------------
250 4 490.5 164.065
500 4 582.5 212.302
750 5 321.6 22.9922
1000 5 344 48.6292
1250 5 321.6 32.5613
1500 5 279.4 13.8795
1750 5 291.8 24.4246
2000 5 308.2 23.0686
2250 5 291.8 13.9771
2500 5 281 28.8375
------------------------------------------------------
On 2019-10-10 18:23, Arcot, Amrita wrote:
Hello,
My name is Amrita and I'm a PhD student at Penn State University. My lab has joined a study currently utilizing PEBL for its cognitive assessment of women of reproductive age. I have been tasked with understanding why a single response SRT would have two responses recorded in a trial. A few papers have suggested computer or keyboard associated latency periods (maybe this results in double depression of the key?). I am quite new to PEBL, and was hoping for guidance on this matter. I have attached a screenshot of four data points to this correspondence. I truly appreciate your help as we continue with this project. Thank you for your time!
Best Regards,
Amrita Arcot
AMRITA ARCOT, RDN, LDN
Ph.D. Student | Department of Nutritional Sciences
The Pennsylvania State University
218 Chandlee Laboratory, University Park, PA 16802
http://nutrition.psu.edu [1]
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------
[1] http://nutrition.psu.edu/
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