working with subsets of timeline variables

[joshkenney]

Hi all,

We are working on a new experiment where the participants initially rate some images. If the participant selects neutral ratings (4,5,6) I manipulate the timeline variable array expStimSubset to move neutral images to the end of the array and remove any non-neutral ratings (1,2,3,7,8,9) from the array:

let likingRating = {
type: "html-keyboard-response",
data: jsPsych.timelineVariable("data"),
stimulus: function(){
var html="<img src='"+jsPsych.timelineVariable('stimulus', true)+"'>";
return html +
"<p> <i> Rate this image from 1 to 9, with 1 indicating that you strongly like the image, 9 indicating that you strongly dislike the image, and 5 indicating that you are neutral towards the image. </i> </p>"
},
on_finish: function(data){
console.log(data.key_press);
console.log(jsPsych.pluginAPI.convertKeyCodeToKeyCharacter(data.key_press));
rating_liking=parseInt(jsPsych.pluginAPI.convertKeyCodeToKeyCharacter(data.key_press));
data.rating_liking=String(jsPsych.pluginAPI.convertKeyCodeToKeyCharacter(data.key_press));
if (data.rating_liking === '4' || data.rating_liking === '5' || data.rating_liking === '6') {
expStimSubset.push(expStimSubset.shift())
} else {
expStimSubset.shift();
}
}
};

jsPsych kindly complains since I have changed shortened the timeline variable when I try to access tuples in expStimSubset array that have been removed:

jspsych.js:554 Uncaught TypeError: Cannot read property 'data' of undefined at TimelineNode.getTimelineVariableValue (jspsych.js:554) at TimelineNode.findTimelineVariable (jspsych.js:560) at TimelineNode.findTimelineVariable (jspsych.js:563) at TimelineNode.timelineVariable (jspsych.js:575) at TimelineNode.timelineVariable (jspsych.js:581) at TimelineNode.timelineVariable (jspsych.js:581) at jspsych.js:306 at evaluateTimelineVariables (jspsych.js:868) at doTrial (jspsych.js:831) at nextTrial (jspsych.js:822)

It seems this is likely a limitation of the timelineVariable (which is initialized at the start of the experiment). Is there a workaround to this problem that anyone has found (or a different implementation)?

Best,
Josh

[joshkenney]

UPDATE: Funny how posting a question to the board 7/10 times ends up answering my own question!

I remembered that I can use jsPsych.endCurrentTimeline() method to handle the error thrown by jsPsych that was preventing me from accessing the empty objects in memory that I shifted out of the timeline variable array expStimSubset in the likingRating object I created above.

Here is my implementation:

let foo = 1;

let subsetRating = {
type: "image-keyboard-response",
data: jsPsych.timelineVariable("data"), //anything marked data in that array will be written to the data file
stimulus: jsPsych.timelineVariable('stimulus'),
prompt: "<p> <i> Rate this image from 1 to 9, with 1 indicating that you strongly like the image, 9 indicating that you strongly dislike the image, and 5 indicating that you are neutral towards the image. </i> </p>",
on_finish: function(data){
console.log(data.key_press); //console.log will print to console the key that was pressed
console.log(jsPsych.pluginAPI.convertKeyCodeToKeyCharacter(data.key_press)); //convirts key press number to 1-9
if (foo >= expStimSubset.length){ // loops through to the end of all possible trials
jsPsych.endCurrentTimeline();
console.log('killProcess');
} else {
foo++;
}
}
};

Hoping someone can benefit from this workaround!