[FieldTrip] ft_redefinetrial and response correctness

Grazia Di Pisa g.dipisa at gmail.com
Fri Oct 30 18:49:31 CET 2015

Hi all,

I have a question about ft_redefinetrial. So, I have two conditions S 11 and S 31, respectively ‘in-synch’ and ’not-in-synch’ and participants were instructed to press 1 or 2 in the keyboard to report their answer, S 1 for ‘not-in-synch’ and S 2 for ‘in-synch’.

What I need to do is TFR analysis only for the trials where participants answered correctly, that is S 11 & S 2 and S 31 & S 1 (below an extract from a .vmrk file showing a correct match).

Mk3=Stimulus,S 11,33182,1,0
Mk4=Stimulus,S 12,33782,1,0
Mk5=Stimulus,S 13,33902,1,0
Mk6=Stimulus,S 14,34582,1,0
Mk7=Stimulus,S  2,37915,1,0

Mk8=Stimulus,S 31,40352,1,0
Mk9=Stimulus,S 63,40952,1,0
Mk10=Stimulus,S 32,40953,1,0
Mk11=Stimulus,S 33,41112,1,0
Mk12=Stimulus,S 35,41792,1,0
Mk13=Stimulus,S 34,41793,1,0
Mk14=Stimulus,S 35,44634,1,0
Mk15=Stimulus,S  1,44635,1,0

From the tutorials, I’ve understood that I should have done this in my trialfun when I defined my trials during the pre-processing step, but today we realised that some subjects perceived as out-of-synch the condition in-synch and viceversa.

So, I was wondering how could I do this now - could I do this using the ft_redefinetrial or worst-case-scenario should I do the pre-processing all over again?

I wrote the code below before starting the TRF analysis but it’s not correct since it’s not working:

%Redefine trials
    cfg = [];
    cfg.trials = 'all';
    cfg.trialdef.eventtype  = 'Stimulus';                     % we are interested in Stimulus markers
    cfg.trialdef.eventvalue = { 'S 11' 'S 31' };
    cfg.trialdef.eventcorrect = [ 'S 2' 'S 1' ]; 		% correct response Stimulus S 2 for S 11 and S 1 for S 31
    cfg.toilim = [-1.8 2.0];                       
    data = ft_redefinetrial(cfg, data);

Any suggestions/help is more than welcome!

thanks in advance,
~ grazia

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