Randomizing trials from separate timelines

[goyals4848]

Hi there! In my task, I show a video and ask a question afterwards. I would like a second question to pop up for a specific subset of video stimuli. What I have done is create two different timelines, and I am trying to intermix and randomize the trials from the conditions. I don't know if this is the best way to do what I want, and I would appreciate any help possible!

Here are the two timelines that I have, but I'm not sure how to create a structure that would combine the individual trials from each timeline.

var test_procedure = {
timeline: [fixation, play_video, response],
timeline_variables: test_stim
}

var full_length_procedure = {
timeline: [fixation, play_full_video, response, emotion_intensity],
timeline_variables: long_stim
}

[becky-gilbert]

Hi @goyals4848, I'm not entirely sure, but I don't think there's an easy way to intermix trials from two separate timelines. What I would do instead is create a single timeline_variables array that contains all of your trials, and add a flag to the trial objects indicating whether or not the second question should be presented. That way, you can add a conditional node in your procedure's timeline that checks whether or not the second question should be presented for that particular trial - if so, present the second question, otherwise skip it. It would look something like this:

// create your test_stim array that contains all of your trial info
// each object contains all of the trial parameters, as well as a 'show_second_question' property that can be true or false
var test_stim = [
  {stimulus: '1', show_second_question: true},
  {stimulus: '2', show_second_question: false}
  // etc.
];

// define all of the parts of your trial procedure...

// conditional node that will go in your procedure timeline
var emotion_intensity_conditional = {
  timeline: [emotion_intensity],
  conditional_function: function() {
    // the variable name you use in the timelineVariable function here should correspond to whatever flag you create in the trial data, 
    // where the value is true if the second question should be shown and false if not
    if (jsPsych.timelineVariable('show_second_question')) {  
      return true;
    } else {
      return false;
    }
  }
};

var test_procedure = {
  timeline: [fixation, play_video, response, emotion_intensity_conditional],
  timeline_variables: test_stim,  
  randomize_order: true // if necessary
}

If you're using a version of jsPsych before 6.3.0, then you'll need to include the second true argument when using jsPsych.timelineVariable inside of the conditional function, i.e. jsPsych.timelineVariable('show_second_question', true).

[goyals4848]

That makes sense! Thank you SO much for the quick and helpful answer!