Putting breaks in a timeline, how?

[DanielBruijn]

So i have another issue: i would like to add breaks in my experiment. I have 384 repetitions of the timeline, and i'd like to put in four breaks, so after every 96 trials. Seems simple, yet i wouldn't know how to let some trial sometimes appear, and sometimes not.

This is my break trial:

timeline: [
      {
        type: 'html-keyboard-response',
        stimulus: [
          "<p style='font-size: 25px'>Time to take a break!</p>" + 
          "<p style='font-size: 25px'>Take a rest for about a minute. Then, Continue by pressing 'C'</p>"
        ],
        choices: "c",
        canvas_size: [1073,1920]
      },
   (...) other trials (...)
  ],
  timeline_variables: full_design,
};
timeline.push(real_trials);

Other people make blocks, and then put a break trial in between, but i'd rather just make the break trial i have conditional on the timeline repetition number. Maybe i could use js.Psych.progress() for that, which returns current_trial_global. That sounds good, but i have no idea how to use that count.

[becky-gilbert]

Hi @DanielBruijn, yes, you can put your break trial inside of a conditional timeline, and then put that conditional timeline inside the trial procedure that uses timeline variables.

When I want to add a break every N trials, what I do is create a global variable to count the trials. In the conditional function, I check if there's a remainder when dividing the current trial count by N - if not then run the break trial, otherwise don't.

So altogether it might look something like this:

var trial_count = 0;

var break_trial = {
  type: 'html-keyboard-response',
  stimulus:  "<p style='font-size: 25px'>Time to take a break!</p>" + 
          "<p style='font-size: 25px'>Take a rest for about a minute. Then, Continue by pressing 'C'</p>",
  choices: "c"
};

var break_conditional = {
  timeline: [break_trial],
  conditional_function: function() {
    // increment trial count - in first run through the timeline variables procedure, trial_count will be equal to 1
    trial_count++;
    if (trial_count % 96 == 0) {
      // if the trial count is divisible by 96, then run the break trial
      return true;
    } else {
      // otherwise skip the break trial
      return false;
    }
  }
];

var real_trials = {
  timeline: [break_conditional, ... other trials ...],
  timeline_variables: full_design
};
timeline.push(real_trials);

You could also do this using jsPsych.progress() and the current_trial_global property, but that's a little trickier to set up because each separate trial in the timeline variables timeline, including the break trials (when they run), will increment this count. So you'd need to factor that in when figuring out the current number of runs through the timeline variables procedure.

[DanielBruijn]

Ahh, okay, i didn't know you could use the conditional_function property in that way. I temporarily fixed it using jsPsych.progress, but that is indeed quite tricky. I'm going to implement this, thank you for your help!
I'll assume it works, and otherwise i'll get back to you. Thanks again!

[DanielBruijn]

Works like a charm! I did change the 96 to 97, otherwise it will throw in one more break just before the end, which seemed odd. Now it's not exactly every quarter, but it's fine.