I don't know how to use conditional

[ler93]

Hi! I find myself stuck in a problem that surely is easy to solve.

The situation is that I must create a stimulus that, depending on the participant's response, takes him to one page or another of the experiment. That is, if the subject answers "yes" to the question, then he should see a new question to answer on the screen. Instead, if his/her answer is "no", should skip that question and continue with the experiment.
The first step I made was to type the following:

var final_questions1 = {
        type: 'html-button-response',
        stimulus: 'While you were reading the phenomenon: Did you remember any of the stories read during the text comprehension activity?',
        choices: ['Yes', 'No'],
    };
    timeline.push (final_questions1);

After this the conditional parameter should go (I guess). If the answer to the last question was "yes", then they should answer this:

var final_questions2 = {
        type: 'survey-text',
        questions: [
          {prompt: '<p> Can you describe in as much detail as possible what was the situation you remembered? </p>',
          columns: 60, rows: 10, required: true, name: 'Memory of situation'}],
          button_label: 'Next>',
    };
    timeline.push (final_questions_conditional);

If instead the answer in "final_questions1" was "no", they should go to another survey-text that continue with the experiment.

I hope I was clear in the description.
From already thank you very much!

[becky-gilbert]

Hi @ler93, you can have a look at the documentation for conditional timelines here.

In your case, the final_questions2 trial should go inside of a conditional node, since that trial should only run under certain conditions. In the conditional_function for your conditional node, you'll want to check what choice was made on the final_questions1 trial. The conditional function should return true if "yes" was selected, and should return false if "no" was selected.

There are a few different ways that you can access the data from the final_questions1 trial. One option is to get all of the jsPsych data with jsPsych.data.get, and then filter the resulting data collection with the filter function. But if final_questions1 always comes immediately before the conditional node in your timeline, then it's probably easier to use the jsPsych.data.getLastTrialData function.

Here's what this looks like all together:

var final_questions1 = {
  type: 'html-button-response',
  stimulus: 'While you were reading the phenomenon: Did you remember any of the stories read during the text comprehension activity?',
  choices: ['Yes', 'No'],  // 'yes' is 0, 'no' is 1
};
timeline.push (final_questions1);

// create this trial but don't add it directly to your main timeline
var final_questions2 = {
  type: 'survey-text',
  questions: [
    {prompt: '<p> Can you describe in as much detail as possible what was the situation you remembered? </p>',
    columns: 60, rows: 10, required: true, name: 'Memory of situation'}],
  button_label: 'Next>',
};

// create a conditional node that contains the final_question2 trial and a conditional function,
// and add this to the main timeline
var final_questions_conditional = {
  timeline: [final_questions2],
  conditional_function() {
    // get the data from the last trial (final_questions1)
    var last_trial_data = jsPsych.data.getLastTrialData().values()[0];
    if (last_trial_data.response == 0) {
      // if the response was choice 0 ("yes"), then run the conditional timeline
      return true;
    } else {
      // otherwise skip the conditional timeline
      return false;
    }
  }
};
timeline.push (final_questions_conditional);

[ler93]

Hi, Becky. I copied the code that you gave me but an error occurs in one of the conditional node line:

    if (last_trial_data.response == 0) {

The error says: Uncaught TypeError: Cannot read property 'response' of undefined

I don't know what could be happening.

[becky-gilbert]

Oops, sorry! I forgot that you need to get the raw data from the data collection that is returned from the jsPsych.data.getLastTrialData function before you can index it and get the response. You can do this using the values function for data collections. So the line that gets the last trial data inside the conditional function should look like this:

var last_trial_data = jsPsych.data.getLastTrialData().values()[0];

I'll edit my response above to avoid confusion.

[ler93]

Thank you very much, Becky! It works perfectly. I'm starting to understand the mechanics behind some jspsych functions and that makes me happy. Thanks a lot for your time!

[becky-gilbert]

No problem! Glad it works now, and sorry for the error in my original response 😬