How come I can only access 39.9% of my array?

[sophief10]

Hello everyone,

I have an array of 1000 data, but for some reason, I can only access 39.9% of these data.

This issue arises in a reaction time game that I am coding. In the game, a user must click a button before an image disappears from their screen. The game is rigged so that the user maintains a 20% success rate across trials.

I accomplish this rigging using ex-Gaussian data. Specifically, I have an array of 1000 ex-Gaussian data, and at the start of each trial, I choose a number from the bottom 20% of these data to represent how long the image will last on the user's screen. The result is that the user will have only a 20% chance of responding to the image quickly enough. The goal of this process is to force the user to have a 20% success rate across trials.

If the user's ongoing success rate happens to be greater than 20%, I decrease the likelihood of succeeding in each trial by 5% until the success rate is 0.2. Similarly, if the user's ongoing success rate is less than 20%, I increase the likelihood of succeeding in a trial by 5% until the success rate is 0.2.

The problem is that I cannot increase the success likelihood past 0.399. It should be able to go all the way up to 1.0, in which case I would be sampling from all of my ex-Gaussian data. However, if I allow my game to run without touching the button, the success likelihood increases in increments of 0.5 - as it should - until it reaches 0.399. Then, it stops increasing.

I do not know why that is happening, or why the success likelihood is even able to be 0.399 when it is supposed to increase in increments of 0.5.

// this is just some supporting code
const jsPsych = initJsPsych();

// the ex-Gaussian data, sorted in ascending order
const dist = [];
for (let i = 0; i < 1000; i++) {
  dist.push(jsPsych.randomization.sampleExGaussian(180, 20, 1, positive = true))
}
dist.sort(function(a, b) {
  return a - b
})

// initial success likelihood = 20%
let success_likelihood = 0.2;

const game = {
  timeline: [{
    // supporting code
    type: jsPsychHtmlButtonResponse,
    choices: ["Click me!"],
    data: {
      type: "game"
    },
    stimulus: "image",
    // *** this is where the problem starts ***
    trial_duration: function() {
      // user must click button within trial duration to succeed on trial
      // trial duration = 20th percentile of dist array
      let cutoff = 1000 * success_likelihood;
      console.log(dist[cutoff - 1])
      return dist[cutoff - 1]
    }
  }],
  on_timeline_finish: function() {
    // evaluate ongoing success rate after each trial
    let total_trials = jsPsych.data.get().filter({
      type: "game"
    });
    let success_trials = total_trials.select('rt').subset(function(x) {
      // if the reaction time (rt) is null, the user failed the trial
      return x != null
    })
    // out of all trials so far, how many were successful?
    let success_rate = success_trials.count() / total_trials.count();
    // adjust success_likelihood to keep it at 0.2
    if (success_rate > 0.2) {
      success_likelihood -= 0.05; // the user is 5% less likely to succeed on a given trial
    } else if (success_rate < 0.2) {
      success_likelihood += 0.05; // the user is 5% more likely to succeed on a given trial
    }
    console.log(success_rate, success_likelihood)
  },
  loop_function: function(data) {
    // supporting code that stops the game after 12 successful trials
    let success_trials = jsPsych.data.get().filter({
      type: "game"
    }).select('rt').subset(function(x) {
      return x != null
    }).count();
    if (success_trials != 12) {
      return true
    } else {
      return false
    }
  }
}

// run code
jsPsych.run([game])

Does anyone know why the access to my array is restricted?

[sophief10]

Update: I solved this issue by changing my code to this:
let cutoff = Math.round(1000 * success_likelihood)
StackOverflow discussion