Stop Signal task,about data collection and interpretation


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Iris520
Iris520
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Hello,everyone.I am a student.I have some problems in data collection and interpretation at Stop Signal task.I don't know why" values.ssd/expressions.p-rs/expressions.ssd、ssrt、sr-rt "show like the following.Is that normal? ssd ranges from 50 to 1150,but,there is always 50...


I am weak at English,hoping you can understand my description.many thanks for your reply.


                                                                                                                                                              Iris





Dave
Dave
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The minimum SSD is 50 ms. Since your data show responses on *every* stop-signal trial (p_rs=100), there is no basis to adjust the SSD upwards.


For details, please refer to the literature, specifically Verbruggen et al. (2008).


Iris520
Iris520
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 so, I needs to change "probability to respond when a stop-signal is present [expressions.p_rs]"?


/ p_rs = (1-(values.ss_ncorr/values.ss_ntotal))*100


But how?


many many thanks...Dave



Dave
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 so, I needs to change "probability to respond when a stop-signal is present [expressions.p_rs]"?


No! You cannot and should not change it. This is an empirical datum. It means the person who produced the data set responded on 100% of stop-signal trials. If a person *never* suppresses a response despite the presence of a stop-signal, there is *no* basis to change the stop-signal-delay.


Your question(s) suggest that you have not yet fully grasped the reasoning behind stop-signal paradigms. I thus urge you to re-read the literature carefully.


Iris520
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I know...When inhibition is successful, SSD increases by 50   msec; when inhibition is unsuccessful, SSD decreases by 50   msec.


but whatever the inhibition is successful or not,the SSD is still stay the minSSD 50msec.I don't know why [:'(]


Dave
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In the data set you posted there is *no successful inhibition*.


Iris520
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OMG ! the problem is the responses. Press the 'D' key with the left index finger when the arrow is pointing to the left 


and press the 'K' key with the right index finger when the arrow is pointing to the right.


but in my computer,the key is useless! so strange!Dave,thank you for all your assistance


Dave
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What are the keyboard scancodes for D & K on your machine (see Tools -> Keyboard Scancodes...) and which scancodes are configured in values.leftkey & values.rightkey in the script's <values> element?


Also note that this does not fit the data set you posted, which clearly shows responses were submitted. If the keys you used were useless, that would not be the case.


Iris520
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thanks,because I already translated this script into Chinese,so there have many problem! I will check it  carefully. thank you again


Iris520
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Hi,Dave,sorry to bother you again.My problem  still needs to be solved.Stop signal task can't run correctly.It seems stop trial can't work——subject can't  suppress all of responses;the value.ssd is always 50.


My computer is Window XP system.one of my friend's window 7 can run correctly,but the other one(window 7)can't work on,it has the same problems as I used describe.I used the original script.Do you know what is the cause may be?


Many thanks in advance




Iris


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