Stop signal task - pre error speeding

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I am working with a choice stop signal task, and need help extracting the RT before an erronous stop trial in order to investigate pre-error speeding.
This is how I extracted the goRT
for y = 1:size(,3)
idx = contains (eegdata.epoch(y).eventtype,'leftGoResponse') | contains(eegdata.epoch(y).eventtype,'rightGoResponse');
if (sum(idx)>0)
RT(y) = eegdata.epoch(y).eventlatency{idx};
RT(y)= nan;
goRT(s) = mean(RT,'omitnan')
The "names" for errounous stop trial is 'stopGoRightFA' and 'stopGoLeftFA'
So I need to extract the goRT before an errounous stop trial, and only that.
Nina Auestad
Nina Auestad on 1 May 2021
Thanks for your comment, allow me to clear things up:
I honestly don't remember why I put the sum in there, it works without. I just put the code there for visual reasons, so that people could see what I am working with. But that's not the problem.
I need to extract the reaction time for responses that were made before unsuccessfull stop trials. What I am struggling with is that the unsuccsessful stops are in a separate epoch. So I need something that will chech if epoch 1 contains 'leftgoresponse' or 'rightgoresponse', and if epoch 2 contains 'stopGoRightFA' and 'stopGoLeftFA' , then return the RT of epoch 1 (eventlatency).
I hope that clears things up?

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Accepted Answer

Jeff Miller
Jeff Miller on 2 May 2021
I think it would be cleanest to start by making a vector to indicate which trials precede unsuccessful stops, which can be done like this (if I have understood everything):
ntrials = size(,3);
PrecedeErrStop = false(ntrials,1);
for y=1:ntrials-1 % the last trial is not followed by anything
PrecedeErrStop(y) = (contains(eegdata.epoch(y).eventtype,'leftGoResponse') | contains(eegdata.epoch(y).eventtype,'rightGoResponse')) ...
& (contains(eegdata.epoch(y+1).eventtype,'stopGoRightFA') | contains(eegdata.epoch(y+1).eventtype,'stopGoLeftFA'));
%PrecedeErrStop is now a vector 1:ntrials where true indicates that the
%trial does precede a stop error and false indicates that it does not.
Then you can select out the RTs that do and do not precede stop errors like this:
PrecedeErrStopRTs = eegdata.epoch(PrecedeErrStop).eventlatency{1};
NotPrecedeErrStopRTs = eegdata.epoch(~PrecedeErrStop).eventlatency{1};
The PrecedeErrStop vector will also be useful if you want to compute ERPs for the error stop trials or to exclude the error stop trials from computation of regular ERPs.
  1 Comment
Nina Auestad
Nina Auestad on 2 May 2021
Thank you!!
I managed to solve it before I saw your response. But I will also try out your code. Might be easier when working with the ERPs as you say!
%% unsuccessful stops
for y = 1:size(,3) - 1;
idx = any(strcmp(eegdata.epoch(y).eventtype,'leftGoResponse')) | any(strcmp(eegdata.epoch(y).eventtype,'rightGoResponse')) && any(contains(eegdata.epoch(y+1).eventtype,'stopGoRightFA')) | any(contains(eegdata.epoch(y+1).eventtype,'stopGoLeftFA'));
if idx;
RT_PreError_us(y) = eegdata.epoch(y).eventlatency{2};
RT_PreError_us(y)= nan;
Preerror_us(s) = (mean(RT_PreError_us, 'omitnan'));

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