use a function output as timelineVariable

[t-09]

Hello everyone! I am coding an experiment in which a participant presses the spacebar as many times as she/he can for 3 trials in a row. Afterwards, I would like to compute the mean of the spacebar presses across the 3 trials and use it as a timelineVariable for the next trials of the experiment. To average across these three trials I use a function, which I call when I declare the timelineVariables. However, the timelineVariable results as 'undefined' (i.e. the trial named below as titration_procedure show the word undefined when the timelineVariable "effort_B" is called, instead of the average of spacebar presses). Can somebody help me?

Here the code:

        var n_compute_max_effort = 3

        var compute_max_effort = {
            type: 'keypress-counter',
            key2press: ['space'],
            num_presses_ends_trial: false,
            trial_duration: 2000,
            post_trial_gap: 2000
        }

        var repeat_max_effort = {
            timeline: [compute_max_effort],
            repetitions: n_compute_max_effort
        }

        function generateMaxEff() {
            try {
                    var keypress_1 = jsPsych.data.getDataByTimelineNode("0.0-1.0-0.0").values()[0].count
                    var keypress_2 = jsPsych.data.getDataByTimelineNode("0.0-1.0-0.1").values()[0].count
                    var keypress_3 = jsPsych.data.getDataByTimelineNode("0.0-1.0-0.2").values()[0].count
                    var tot_presses = keypress_1 + keypress_2 + keypress_3
                    var avg_presses = tot_presses / n_compute_max_effort
                    console.log(avg_presses)
                    return avg_presses
                } catch (err){
                    console.log('Max effort not yet estimated')
                }            
        }
        var titration_procedure = {
            type: 'html-button-response',
            choices: function (){ 
               return ['<p style="font-size: 48px;">Offerta A: <br><br><b>'+jsPsych.timelineVariable('effort_A', true)+'</b> pressioni <br>per <br><b>'+jsPsych.timelineVariable('offer_A', true)+'</b> euro</p>', 
                    '<p style="font-size: 48px;">Offerta B: <br><br><b>'+jsPsych.timelineVariable('effort_B', true)+'</b> pressioni <br>per <br><b>'+jsPsych.timelineVariable('offer_B', true)+'</b> euro</p>'
                ]
            },            
            prompt: '<p style="font-size: 32px;">Quale offerta preferisci?</p>',
            data: {
                do_the_effort: jsPsych.timelineVariable('is_effort_required')
            }        
        }

        var spacebar_pression = {
            type: 'keypress-counter',
            key2press: ['space'],
            num_presses_ends_trial: true,
            num_presses: function() {
                var sc = jsPsych.data.getLastTrialData().values()[0].effort_required
                return sc
            },
            trial_duration: 2000
        }

        var effort = {
            timeline: [spacebar_pression],
            conditional_function: function(){
                var is_eff_req = jsPsych.data.getLastTrialData().values()[0].do_the_effort;
                if(is_eff_req){
                    return true;
                } else {
                    return false;
                }
            }
        }

        var main_procedure = {
            timeline: [titration_procedure, effort],
            timeline_variables: [
                {effort_A: 2, effort_B: generateMaxEff(), offer_A: 33, offer_B: 72, is_effort_required: false},
            ],
            // randomize_order: true       
        }
        
        
        jsPsych.init({
            timeline: [fullscreen_trial, repeat_max_effort, main_procedure, fullscreen_trial_exit],          
            on_finish: function(){jsPsych.data.displayData();}
        })
`

[jodeleeuw]

Hi @t-09,

The problem here is that this chunk of code runs before the experiment starts:

var main_procedure = {
            timeline: [titration_procedure, effort],
            timeline_variables: [
                {effort_A: 2, effort_B: generateMaxEff(), offer_A: 33, offer_B: 72, is_effort_required: false},
            ],
            // randomize_order: true       
        }

Which means that generateMaxEff() is called before any data exist.

Since you are computing this value dynamically I'm not sure if you need to use a timeline variable. Could you just do something like this instead?

var titration_procedure = {
            type: 'html-button-response',
            choices: function (){ 
		var effortB = generateMaxEff();
               return ['<p style="font-size: 48px;">Offerta A: <br><br><b>'+jsPsych.timelineVariable('effort_A', true)+'</b> pressioni <br>per <br><b>'+jsPsych.timelineVariable('offer_A', true)+'</b> euro</p>', 
                    '<p style="font-size: 48px;">Offerta B: <br><br><b>'+effortB+'</b> pressioni <br>per <br><b>'+jsPsych.timelineVariable('offer_B', true)+'</b> euro</p>'
                ]
            },            
            prompt: '<p style="font-size: 32px;">Quale offerta preferisci?</p>',
            data: {
                do_the_effort: jsPsych.timelineVariable('is_effort_required')
            }        
        }

[t-09]

Hi Josh!
Many thanks for your reply, your solution works perfectly!

Cheers!