[FieldTrip] Baseline correction on TFR with baseline period in separate trial

[mp95kexi at studserv.uni-leipzig.de]

Hi Fieldtrippers!

I am quite new to fieldtrip and coding and would love some help and/or  
suggestions. I am investigating brain mechanism behind binary  
communication, more precisely I am trying to distinguish positive  
answers from negative ones.

I have data from 3 patients and at the moment want to conduct a  
between trial single subject comparison.

The paradigm of my data is generally :

Trigger S 10 or S 11: baseline period (5-10s) --- Trigger S5 or S6:  
Question period (length varies) ---- Trigger S 4 or S 8: Thinking  
period (10-15s)

I have preprocessed the data, defining trials at baseline triggers and  
thinking triggers like this:

         cfg = [];
         cfg.dataset = vhdrFile;
         cfg.trialfun = 'ft_trialfun_general';
         cfg.trialdef.eventtype = 'Stimulus';
         cfg.trialdef.eventvalue = {'S  4' 'S  8' 'S 10' 'S 11'};
         % thinking trigger: S4 for yes answers, S8 for no,
         % baseline trigger: S10 before yes question/answer, S11 for no
         cfg.trialdef.prestim = 2;
         cfg.trialdef.poststim = 5; % only first 3 seconds plus 2 sec padding
         cfg = ft_definetrial(cfg);

         cfg.continuous = 'yes';
         cfg.channel = {'all'}; % only EEG
         cfg.detrend = 'yes';
         cfg.demean = 'yes';
         cfg.reref = 'yes';
         cfg.refchannel = 'all';
         cfg.refmethod = 'avg';
         cfg.bpfilter = 'yes';
         cfg.bpfiltord = 3;
         cfg.bpfilttype = 'but';
         cfg.bpfreq = [0.5 45];
         cfg.dftfilter = 'yes';
         cfg.dftfreq = [50 100];

         % save data in same location as its corresponding file
         [~, fileName, ~] = fileparts(vhdrFile);
         cfg.outputfile = fullfile(vhdrFiles(i).folder, [fileName, '_data']);
         ft_preprocessing(cfg);

Next I did a TF decomposition, below are the settings I have used

     cfg         = [];
     cfg.method  = 'mtmconvol';
     cfg.output  = 'pow'; % return power-spectra
     cfg.channel = 'all';
     cfg.trials  = 'all';
     cfg.keeptrials = 'no'; % 'yes' for cluster based permuatation  
test between trials, 'no' results in average
     cfg.taper   = 'hamming';
     cfg.foi     = 1:45;
     cfg.t_ftimwin = ones(length(cfg.foi),1); % length of time window 1 sec
     cfg.toi = -1:0.05:3;

     cfg.trials       = find(data.trialinfo(:,1) == 4);
     tfdata_yes = ft_freqanalysis(cfg, data);

     cfg.trials       = find(data.trialinfo(:,1) == 8);
     tfdata_no = ft_freqanalysis(cfg, data);


Now I want to dB baseline correct the thinking epochs (S4 and S8)  
using the baseline epochs (S10 and S11). From what I could find  
online, usually one would use pre-stimulus period for baseline  
correction. With my data, the pre-stimulus period is inside the  
question period hence why there is another baseline period before  
that. I am quite confused on how to do this correctly.

I'd really appreciate any ideas on this,
Meedy