Conditional trial after every Nth item in timeline

[ghost]

Hi, I would like to add a conditional trial to the end of the timeline which only runs after every 8th timeline variable is selected, as proposed in this old Google Groups thread. I just can't seem to figure out how to accomplish this (still very new to JavaScript/jsPsych).

My timeline now looks like this:

timeline.push({
    timeline: [
      {
        type: 'html-keyboard-response',
        stimulus: "<div style='font-size:32px;'>+</div>",
        choices: jsPsych.NO_KEYS,
        trial_duration: 1000
      },
      { 
        type: 'audio-keyboard-response',
        stimulus: jsPsych.timelineVariable('audio'),
        choices: jsPsych.NO_KEYS,
        trial_ends_after_audio: true
      },
      { 
        type: 'html-button-response',
        stimulus: "<p>Which question did the speaker answer?<br></p>",
        choices: [jsPsych.timelineVariable('questionBF'),
                  jsPsych.timelineVariable('questionSF'), 
                  jsPsych.timelineVariable('questionVF'), 
                  jsPsych.timelineVariable('questionOF')],
        button_html: '<button class="jspsych-btn-block">%choice%</button>', 
        margin_vertical: '12px',
        data: jsPsych.timelineVariable('data'),
        on_finish: function(data){
          if(data.button_pressed == data.correct_button){
            data.correct = true;
          } else {
            data.correct = false;
          }
        }
      }
    ],
    // timeline_variables: [ ],
    sample: {
      type: 'custom',
      fn: function(){
            var groups = [[0,1,2,3],[4,5,6,7],[8,9,10,11],[12,13,14,15],[16,17,18,19],[20,21,22,23],[24,25,26,27],[28,29,30,31]];
            var all_items = [];
            for(var i=0; i<groups.length; i++){ 
                    for(var j=0; j<groups[i].length; j++){
                                all_items.push({group: i, trial_num: groups[i][j]});
                    }
            }
            var order = jsPsych.randomization.shuffleNoRepeats(all_items, function(a,b){ 
                    return a.group == b.group;
            });
            return order.map(function(x){ return x.trial_num }); 
      }
    }  
  }); 

I want the conditional trial to be added to the end of the timeline so it will be displayed after participants give a button response (the html-button-response trial) and it should only be displayed after every 8th item (items are randomly selected with group constraints from the array of 32 items). Any suggestions?

[jodeleeuw]

One solution is to somehow get the conditional function to count how many iterations through the timeline have happened so far, and if it is divisible by 8 then we should show the conditional trial.

To do this, I needed to add some kind of marker to the data that would exist once for each loop. You might already have such a marker in jsPsych.timelineVariable('data'). Since I couldn't see what was in those variables I added one to the fixation trial: data: {phase: 'fixation'}.

In the conditional function, I used jsPsych.data.get().filter({phase: 'fixation'}).count() to count the number of fixation trials so far. I just return this value % 8, which should be true after every 8 trials.

timeline.push({
    timeline: [
      {
        type: 'html-keyboard-response',
        stimulus: "<div style='font-size:32px;'>+</div>",
        choices: jsPsych.NO_KEYS,
        trial_duration: 1000,
	data: {phase: 'fixation'}
      },
      { 
        type: 'audio-keyboard-response',
        stimulus: jsPsych.timelineVariable('audio'),
        choices: jsPsych.NO_KEYS,
        trial_ends_after_audio: true
      },
      { 
        type: 'html-button-response',
        stimulus: "<p>Which question did the speaker answer?<br></p>",
        choices: [jsPsych.timelineVariable('questionBF'),
                  jsPsych.timelineVariable('questionSF'), 
                  jsPsych.timelineVariable('questionVF'), 
                  jsPsych.timelineVariable('questionOF')],
        button_html: '<button class="jspsych-btn-block">%choice%</button>', 
        margin_vertical: '12px',
        data: jsPsych.timelineVariable('data'),
        on_finish: function(data){
          if(data.button_pressed == data.correct_button){
            data.correct = true;
          } else {
            data.correct = false;
          }
        }
      },
	{
		timeline: [...]
		conditional_function: function(){
			return jsPsych.data.get().filter({phase: 'fixation'}).count() % 8 == 0;
		}
	}
    ],
    // timeline_variables: [ ],
    sample: {
      type: 'custom',
      fn: function(){
            var groups = [[0,1,2,3],[4,5,6,7],[8,9,10,11],[12,13,14,15],[16,17,18,19],[20,21,22,23],[24,25,26,27],[28,29,30,31]];
            var all_items = [];
            for(var i=0; i<groups.length; i++){ 
                    for(var j=0; j<groups[i].length; j++){
                                all_items.push({group: i, trial_num: groups[i][j]});
                    }
            }
            var order = jsPsych.randomization.shuffleNoRepeats(all_items, function(a,b){ 
                    return a.group == b.group;
            });
            return order.map(function(x){ return x.trial_num }); 
      }
    }  
  }); 

[ghost]

This was doing the opposite, so it showed the conditional trial after every trial except after the 8th. I made some changes and now it works. Not sure if this is the correct way to do it, but here's the conditional trial code which made it work:

{
        timeline: [ ... ],
        conditional_function: function(){
            if(jsPsych.data.get().filter({phase: 'fixation'}).count() % 8){
              return false;
            } else {
              return true;
            }
        }
}

[jodeleeuw]

Ack, sorry for my sloppy code. Glad you figured it out! I'm updating the answer.