XPLab_2019

Course site for "Experimental Psychology Lab" 2019

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In-class exercises May 16th 2019

In today’s class you are going to adapt your Mental Rotation task in a number of steps, working towards a realization of the whole experiment.

Update your current experiment to _babe 0.1.0

• change file packages.json to include:

"dependencies": {
  "babe-project": "~0.1.0"
}

• run npm install again
• change your view instantiations
  • where you previously had babeViews.Intro({XYZ}), you would now have babeViews.view_generator('intro', {XYZ})
  • see https://babe-project.github.io/babe-docs/01_designing_experiments/01_template_views/
• (optional) change the file names in accordance with the new departure point:
  • https://github.com/babe-project/departure-point

Add a lag to your key-press main task

• read the documentation on life cycles:
  • https://babe-project.github.io/babe-docs/01_designing_experiments/04_lifecycles_hooks/
• realize a 1 second inter-trial pause & a 500 ms fixation cross for your key-press task

Add a practice session

Practice is exactly like the main task, but we will use a hook to control for correctness.

• read the part about hooks on https://babe-project.github.io/babe-docs/01_designing_experiments/04_lifecycles_hooks/
• use the after_response_enabled hook to realize a check of correctness for the practice trials
• to do this, first add to the practice trials the information which answer is correct; store it in a field called correct, as part of each trial object
• the function given in the docs on hooks works for a forced choice task, but not for a key_press view because the latter has a different response function; use instead the following function:

const check_response = function(data, next) {
    data.response_checked = false;
    $("body").on("keydown", function(e) {
        if (data.response_checked == false) {
            const keyPressed = String.fromCharCode(
                e.which
            ).toLowerCase();
            if (keyPressed == data.key1 || keyPressed == data.key2) {
                if (data[keyPressed] === data.correct) {
                    alert('Your answer is correct! Yey!');
                } else {
                    alert('Sorry, this answer is incorrect :( The correct answer was ' + data.correct);
                }
                data.response_checked = true;
                next();
            }
        }})
}

Add wrapping views & instructions

• structure your experiment by adding appropriate wrapper views, for example:
  • inform your participants that now the practice starts
  • inform your participants that practice is now over and the main show starts
  • …
• your instructions should make participants understand the task quickly

Include all items

• include all items (12 practice and 48 main)
• make sure that the sequence of presentation is randomized

Check the experiment

• do the whole experiment in debug mode at least twice
• save the data, load it into R and check whether everything seems correct:
  • is everything of relevance recorded?
  • is trial sequence randomized?
  • is each picture presented exactly once for each participant?
  • …