Error during regression Analysis of EEG data

I have been trying to run the regression analysis of EEG data and for the regressand(dependant variable) t-test, I tried running the below loop but I keep running into error. Can someone identify where I'm going wrong, please?

for ichan = 1:size(freqres.powspctrm,1)
    for ifrq = 1:size(freqres.powspctrm,4)

cfg                     = [];
cfg.previous            = freqres.cfg;
cfg.channel             = freqres.label;
cfg.frequency           = [2 40]; 
cfg.method              = 'analytic';
cfg.statistic           = 'depsamplesT';     
cfg.alpha               = 0.05;
cfg.tail                = 1;
cfg.correctm            = 'no';

   Nsub = 11;
   cfg.design(1,1:2*Nsub)  = [ones(1,Nsub) 2*ones(1,Nsub)];
   cfg.design(2,1:2*Nsub)  = [1:Nsub 1:Nsub];
   cfg.ivar                = 1; % the 1st row in cfg.design contains the independent variable
   cfg.uvar                = 2; % the 2nd row in cfg.design contains the subject number

   stat = ft_timelockstatistics(cfg,ichan{:}, ifrq{:});
      end
  end

[Geoff Hayes]

Maazah - what is the error that you are observing? Please describe it and include the full error message. If the behaviour is unexpected, then describe the desired behaviour.

[Maazah Ali]

Hi Geoff, I am trying to run a regression analysis on EEG data. I have used search preference as the predictor and data as the regressand. This is the code I'm using:

predictor = searchpref'
predictor = predictor(:);

ichan = 117;

data =(ichan, ifrq);

for ichan = 1:size(freqres.powspctrm,2)
    for ifrq = 1:size(freqres.powspctrm,4)
cfg                     = [];
cfg.previous            = freqres.cfg;
cfg.channel             = freqres.label;
cfg.frequency           = [2 40]; 
cfg.method              = 'analytic';
cfg.statistic           = 'depsamplesT';     
cfg.alpha               = 0.05;
cfg.tail                = 1;
cfg.correctm            = 'no';

%  Nsub = 11;
%  cfg.design(1,1:2*Nsub)  = [ones(1,Nsub) 2*ones(1,Nsub)];
%  cfg.design(2,1:2*Nsub)  = [1:Nsub 1:Nsub];
%  cfg.ivar                = 1; 
%  cfg.uvar                = 2; 
%  

      end
  end

stat = ft_timelockstatistics(cfg,searchpref, data);

However, MATLAB seems to give an error for the last line and won't run the regression t-test.

Error in Regression_searchpreference (line 70)
stat = ft_timelockstatistics(cfg,predictor,data)

If you could identify the problem, I would be very grateful. Many thanks.

Answer 1

[Walter Roberson]

That appears to be a reference to the third party FieldTrip Toolbox

Your for loops on ichan and ifrq are over integers, 1 to the size of something. But your call has

   stat = ft_timelockstatistics(cfg,ichan{:}, ifrq{:});

the {:} is only valid for cell arrays, but you are using {:} on those integers.

Your size are over freqres.powspctrm which must be at least 4 dimensional, so it is not obvious to me what you would be trying to index as a cell array. Maybe

   stat  = ft_timelockstatistics(cfg, freqres.powspctrm{ichan, :, :, ifrq})