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(eegdata.data,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};
else
RT(y)= nan;
end
end
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.
2 Comments
Jeff Miller
on 30 Apr 2021
Is idx a single boolean just for trial y, or is it a vector? I would have thought it was just a single boolean, but sum(idx) would be unnecessary in that case, so I am confused.
Accepted Answer
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(eegdata.data,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'));
end
%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.
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