Counterbalancing variables?

[princessc...@gmail.com]

Sorry if this has been answered before but I can't seem to find an answer. I would like to counterbalance the order in which experimental variables are displayed. For example I have two variables:

var variable1 = {

    timeline: [

        {

            type: 'html-keyboard-response',

            stimulus: '+',

            choices: jsPsych.NO_KEYS,

            trial_duration: 200

        },

        {

            type: 'image-keyboard-response',

            stimulus: jsPsych.timelineVariable('picture'),

            trial_duration: 2000,

            choices: [37, 39]

        },

    ],

    timeline_variables: [

        {picture: 'picture1.png' },

        { picture:'picture2.png' },

      ],

      randomize_order:true,

      repetitions:8

}

var variable2 = {

    timeline: [

        {

            type: 'html-keyboard-response',

            stimulus: '+',

            choices: jsPsych.NO_KEYS,

            trial_duration: 200

        },

        {

            type: 'image-keyboard-response',

            stimulus: jsPsych.timelineVariable('picture'),

            trial_duration: 2000,

            choices: [37, 39]

        },

    ],

    timeline_variables: [

        {picture: 'picture3.png' },

        { picture:'picture4.png' },

      ],

      randomize_order:true,

      repetitions:16

}

I would like to randomly display the variables in the experiment, so sometimes variable1 comes first, and sometimes variable 2. This seems very easy but somehow I can't get it to work? Any suggestions would be appreciated! Thanks!!!!

[Josh de Leeuw]

Hi,

One solution would be to randomly sample from the set of variables and then only push the selection onto the timeline.

var timeline = [ ... ] // other trials might be in here

var random_sample = jsPsych.randomization.sampleWithoutReplacement([variable1, variable2], 1); // generates an array of length 1

timeline = timeline.concat(random_sample);

Cheers,

Josh

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