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Tutorial: Simple Experiment

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Summary of tutorial content

Pushkin’s modularity means that, in principle, you could probably use any javascript-based experiment engine to write your experiments. However, we highly recommend using jsPsycharrow-up-right. Pushkin has only been extensively tested with jsPsych, and all the documentation currently assumes you are using jsPsych.

The tutorial below starts with a simple lexical decision task written in plain jsPsych 7. The tutorial below explains how to modify this code to run in Pushkin. This is a recommended tutorial for learning the ropes, but a more complete experiment template for lexical decision is available to install through Pushkin (read more)

If you are not familiar with jsPsych, please consult the documentationarrow-up-right first. We recommend you also walk through some of the tutorials.

Note: As of v3.6.0 of the Pushkin CLI, the procedures described here for moving the timeline and importing plugins can be automated if you choose to import a jsPsych experiment when you run pushkin install experiment and select the basic template (v5+). You can still do these manually if you choose. You may also need to do parts of these procedures in the course of modifying one of the other experiment templates.

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Initial code

We will start with a simple lexical decision experiment. The code has been adapted from the experiment herearrow-up-right in order to be compatible with jsPsych 7. You can save the code below as an .html file to run it as a standalone jsPsych experiment:

<!DOCTYPE html>
<html>
  <head>
    <title>My experiment</title>
    <script src="https://unpkg.com/jspsych@7.3.3"></script>
    <script src="https://unpkg.com/@jspsych/plugin-html-keyboard-response@1.1.2"></script>
    <link
      href="https://unpkg.com/jspsych@7.3.3/css/jspsych.css"
      rel="stylesheet"
      type="text/css"
    />
    <style>
      .fixation {
        border: 2px solid black;
        height: 100px;
        width: 200px;
        font-size: 24px;
        position: relative;
        margin: auto;
      }
      .fixation p {
        width: 100%;
        position: absolute;
        margin: 0.25em;
      }
      .fixation p.top {
        top: 0px;
      }
      .fixation p.bottom {
        bottom: 0px;
      }
      .correct {
        border-color: green;
      }
      .incorrect {
        border-color: red;
      }
    </style>
  </head>
  <body></body>
  <script>
    const jsPsych = initJsPsych();

    const timeline = [];

    var welcome = {
      type: jsPsychHtmlKeyboardResponse,
      stimulus: consent + "<p>Press spacebar to continue.</p>",
      choices: [" "],
    };

    timeline.push(welcome);

    var instructions_1 = {
      type: jsPsychHtmlKeyboardResponse,
      stimulus: `
        <p>You will see two sets of letters displayed in a box, like this:</p>
        <div class="fixation"><p class="top">HELLO</p><p class="bottom">WORLD</p></div>
        <p>Press Y if both sets are valid English words. Press N if one or both is not a word.</p>
        <p>Press Y to continue.</p>
      `,
      choices: ["y"],
    };

    timeline.push(instructions_1);

    var instructions_2 = {
      type: jsPsychHtmlKeyboardResponse,
      stimulus: `
        <p>In this case, you would press N.</p>
        <div class="fixation"><p class="top">FOOB</p><p class="bottom">ARTIST</p></div>
        <p>Press N to begin the experiment.</p>
      `,
      choices: ["n"],
    };

    timeline.push(instructions_2);

    var lexical_decision_procedure = {
      timeline: [
        {
          type: jsPsychHtmlKeyboardResponse,
          stimulus: '<div class="fixation"></div>',
          choices: "NO_KEYS",
          trial_duration: 1000,
        },
        {
          type: jsPsychHtmlKeyboardResponse,
          stimulus: function () {
            let first_word = jsPsych.timelineVariable("word_1");
            let second_word = jsPsych.timelineVariable("word_2");
            first_word =
              '<div class="fixation"><p class="top">' + first_word + "</p>";
            second_word =
              '<div class="fixation"><p class="bottom">' + second_word + "</p>";
            return first_word + second_word;
          },
          choices: ["y", "n"],
          data: {
            both_words: jsPsych.timelineVariable("both_words"),
            related: jsPsych.timelineVariable("related"),
          },
          on_finish: function (data) {
            if (data.both_words) {
              data.correct = jsPsych.pluginAPI.compareKeys(data.response, "y");
            } else {
              data.correct = jsPsych.pluginAPI.compareKeys(data.response, "n");
            }
          },
        },
        {
          type: jsPsychHtmlKeyboardResponse,
          stimulus: function () {
            let last_correct = jsPsych.data
              .getLastTrialData()
              .values()[0].correct;
            if (last_correct) {
              return '<div class="fixation correct"></div>';
            } else {
              return '<div class="fixation incorrect"></div>';
            }
          },
          choices: "NO_KEYS",
          trial_duration: 2000,
        },
      ],
      timeline_variables: stimArray,
      randomize_order: true,
    };

    timeline.push(lexical_decision_procedure);

    var data_summary = {
      type: jsPsychHtmlKeyboardResponse,
      stimulus: function () {
        // Calculate performance on task
        let correct_related = jsPsych.data
          .get()
          .filter({ related: true, correct: true })
          .count();
        let total_related = jsPsych.data
          .get()
          .filter({ related: true })
          .count();
        let mean_rt_related = jsPsych.data
          .get()
          .filter({ related: true, correct: true })
          .select("rt")
          .mean();

        let correct_unrelated = jsPsych.data
          .get()
          .filter({ related: false, both_words: true, correct: true })
          .count();
        let total_unrelated = jsPsych.data
          .get()
          .filter({ related: false, both_words: true })
          .count();
        let mean_rt_unrelated = jsPsych.data
          .get()
          .filter({ related: false, both_words: true, correct: true })
          .select("rt")
          .mean();

        // Show results and debrief
        let results = `<p>You were correct on ${correct_related} of ${total_related} related word pairings!
            Your average correct response time for these was ${Math.round(
              mean_rt_related
            )} milliseconds.</p>
            <p>For unrelated word pairings, you were correct on ${correct_unrelated} of ${total_unrelated}!
            Your average correct response time for these was ${Math.round(
              mean_rt_unrelated
            )} milliseconds.</p>`;
        return results + debrief;
      },
      choices: "NO_KEYS",
    };

    timeline.push(data_summary);

    jsPsych.run(timeline);
  </script>
</html>

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Move the timeline

Follow the Quickstart through pushkin install site or navigate to the root directory of an existing site. Create a new experiment named "lex" and select the latest version of the basic template:

You should now have a folder experiments/lex with the following content:

Open experiment.js. It should look like this:

From the jsPsych code above, copy everything between const timeline = [] and jsPsych.run(timeline); (excluding those lines). Paste those lines into /experiments/lex/web page/src/experiment.js (replacing the existing content) between const timeline = [] and return timeline. Thus you should now have a function createTimeline() within which you build up and finally return the timeline for the experiment.

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Import plugins

In the jsPsych code above, plugins are loaded with <script> tags. In a Pushkin experiment, plugins are loaded with import statements. The basic template already includes the html-keyboard-response plugin as a dependency, so no additional modifications are needed. If you wanted to add additional jsPsych plugins to this experiment, you would simply use additional import statements in the same format (see examples here).

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Moving CSS styling

The experiment above relies on CSS styling described in a <style> tag to display the experiment correctly. This styling needs be moved to /experiments/lex/web page/src/assets/experiment.css in order to apply your Pushkin experiment. The new CSS file will look like:

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