Setting up your code to collect good EEG data

sending triggers

For EEG timing is of the essence! Even if you do not care about exact stimulus timing, you really should care about logging the time relevant events happen as accurately as possible!

Documentation and code for how to send triggers with labjack

Example Code MatlabExample Code Python

Here's some example code for how to define and send triggers in Matlab. For this to work, make sure you have downloaded the code for labjack to your task code folder and added the path (see example).

Note

Matlab example contributed by Romy Froemer.

    %% setting EEG via console prompt at the start of the task
    novalidinput = 1;
    while  novalidinput==1
        expParams.isEEGsession = (input('Do EEG? y or n: ','s'));

        if isstrprop(p.isET, 'upper')
            expParams.isEEGsession = lower(expParams.isEEGsession);
        end

        if strcmp(expParams.isEEGsession, 'y')
            expParams.isEEGsession = 1;
            novalidinput = 0;
        elseif strcmp(expParams.isEEGsession, 'n')
            expParams.isEEGsession=0;
            novalidinput = 0;
        end
    end

    %% setting up the EEG
    if expParams.isEEGsession
        addpath('taskCode/EEG_code/'); % in this example, the labjack code lives in a folder called EEG_code within a folder called taskCode

        if expParams.isEEGsession

            try
                L = lab_init_sa;
                expParams.EEGpars.ext.L = L;
                disp('EEG SUCCESSFULLY CONFUFURED!');
                % here also define event codes
                % 1x = stimulus onset, 2x = response onset; Confidence = trig +20
                % x = phase: FAM = 1, RATE = 2, CHOICE = 0

                % FAM triggers
                expParams.EEGpars.trigs.FamStimCode = 11; % a task relevant stimulus comes on - Choice
                expParams.EEGpars.trigs.FamRespCode = 21; % a response is given

                % RATE Triggers
                expParams.EEGpars.trigs.RateStimCode = 12;
                expParams.EEGpars.trigs.RateRespCode = 22; % -  RATE
                expParams.EEGpars.trigs.ConfPromptCode = 32;
                expParams.EEGpars.trigs.ConfRespCode = 42;

                % CHOICE Triggers
                expParams.EEGpars.trigs.trialCode = 1;      % a trial begins (first item)
                expParams.EEGpars.trigs.stimCode = 10;      % a task relevant stimulus comes on - Choice (all items after first)
                expParams.EEGpars.trigs.respCode = 20;      % a response is given
                expParams.EEGpars.trigs.fbCode = 30;        % show chosen
                expParams.EEGpars.trigs.erCode = 40;        % error response code
                expParams.EEGpars.trigs.NOrespCode = 99;    % trial ended without a response


                expParams.EEGpars.trigs.runStartCode = 50;
                expParams.EEGpars.trigs.runEndCode = 60;
            catch
                disp('FAILED EEG CONFIGURATION!  :-(');
            end


            try
                % Turn off all pins in the parallel port
                lab_put_code_sa(expParams.EEGpars.ext.L,0); 
                disp('EEG TRIGGER SUCCESSFUL!');
            catch
                disp('FAILED EEG TRIGGER!  :-(');
            end


        end
    end

    %% Sending an actual trigger (example)


        % here's where stimuli are actually shown
        Screen(p.wPtr, 'Flip',0,1);  % don't clear!

        if expParams.isEEGsession && ~expParams.CHOICE.isPracticeNow
            lab_put_code_sa(expParams.EEGpars.ext.L,expParams.EEGpars.trigs.trialCode);
        end

Here's some example code for how to send triggers in python. All following Python code snippets are from Python code elements run by Opensesame.

1) Import the labjackU3 module at the beginning of the experiment:

    import labjackU3

2) Insert a Python code element in the trial sequence at exactly the moment you want to sent the trigger and sent the trigger you want from that code element. In this example the trigger “99” is sent everytime the Python code element is executed within the trial sequence:

    labjackU3.trigger(99) 

The triggers can be either hard-coded as in the example above or soft-coded and defined somewhere else, as in the following example. Here the trigger with information about the memory array is defined somewhere else in the experiment (e.g. the run file) in a variable named “trigger_ma_info”:

    labjackU3.trigger(trigger_ma_info)

Example of a trial sequence in opensesame, to illustrate the placement of the python code snippets.

Caveat: LabJack has a sleep time implemented this will influence the timing of your task, as the python code sending the trigger is paused after sending it, this could become relevant for experiments that need highly precise timing. The pause duration of LabJack can be changed with a line of code that is inserted after importing the LabJack module. In this example the pause time is reduced to 2.5ms.

    labjackU3.DURATION = 0.025

When triggers are sent closely after the LabJack pause might not be sufficient to prevent trigger overlap, so you can either increase the labjackU3.DURATION or you use the opensesesame module “time” to pause the experiment. To do that you need to import “time” at the beginning of the experiment and set it to sleep after sending a trigger. In this example, time is paused for 5ms.

    import time

     time.sleep(0.05) 

stimulus timing