Week 7 practical

Audio, trial data again, saving data to the server trial by trial

The plan for week 7 practical

This week we are going to look at code for a perceptual learning experiment based on the experiment described in Levi-Ari (2017) (and in fact using her stims, see below). There’s no new material to look at in the Online Experiments with jsPsych tutorial, although we will be using code from Section 06 of that tutorial that you read for week 6, you could remind yourself of that if you want. The perceptual learning uses the audio-button-response plugin to play audio and get button-click responses, we haven’t used it before but it works in basically the same way as other plugins you have used. We are also going to reuse some code from the word learning experiment to handle randomisation of button positions and using data to keep track of which buttons appeared where. The main new things we’ll introduce are the audio (but jsPsych makes that very easy), buttons which are images rather than text, and also saving data trial-by-trial to the server rather than waiting till the end and dumping it all in one go.

Remember, as usual the idea is that you do as much of this as you can on your own (might be none of it, might be all of it) and then come to the practical drop-in sessions or use the chat on Teams to get help with stuff you need help with.


Dr. Shiri Lev-Ari (who is obviously the author of Lev-Ari, 2017) very kindly shared the audio stimuli for her experiment and gave me permission to make them public here, so the code uses the same audio files as the real experiment. Shiri wasn’t able to share the visual stims since she didn’t have sharing permission for all of them, but my research assistant Rachel Kindellan did some epic google image searching and found equivalent images which are licensed to be shared - so the images are not identical to the ones used by Shiri, but should be close enough to give you a feel for the experiment.

A perceptual learning experiment

Getting started

As usual, I’d like you to download and run the code I provide, look at how the code works, and then attempt the exercises below, which involve editing the code in simple ways.

You need a bunch of files for this experiment - as per last week, an html file, a js file, a php file (for saving data), and then several folders containing images and sound files. Again, rather than downloading them individually, download the following zip file and then uncompress it into your usual jspsych folder:

Again, the code makes some assumptions about the directory structure it’s going to live in - you need to extract these files to a folder called something like perceptual_learning, alongside your grammaticality_judgments, self_paced_reading, word_learning and jspsych-6.1.0 folders.

For the first time, this code will not run on your local computer - you need to upload the whole perceptual_learning folder to your public_html folder on the jspsychlearning server and play with it there (if your directory structure is as suggested the url for your experiment will be http://jspsychlearning.ppls.ed.ac.uk/~UUN/perceptual_learning/perceptual_learning.html where UUN is your UUN). This is a recurring problem to do with the way jsPsych handles audio, it’s actually a bit mysterious to me (other stuff I do with audio works OK locally), but it restricts us to running this code on the server. As per last week, the code for saving data to the server only works on the server anyway.

Finally, there is one tweak you need to make before your data will save:

First, get the code and run through it so you can check it runs, and you can see what it does. Then take a look at the HTML and js files in your code editor (e.g. Atom), and read on.

Structure of the experiment

The experiment consists of three stages:

Social network questionnaire

The full set of questions is available in the supporting information of Lev-Ari (2017). As you can see, there are various text-box questions which are easy enough to implement in jsPsych using the survey-html-form plugin (look again at the end of the week 4 practical). In the code I have only implemented the first three questions, which all require numeric answers:

var social_network_questionnaire = {
  type: 'survey-html-form',
  preamble: "<p style='text-align:left'> <b>Social network questionnaire</b></p>\
             <p style='text-align:left'> In this questionnaire we would like to \
             gather information about your linguistic interactions. We realize \
             that some of the estimates are difficult to make. Please do your \
             best and be as accurate as possible.</p> \
             <p style='text-align:left'> Important: When providing estimates for \
             your exposure in a week, keep in mind that your habits may vary \
             considerably depending on the day of the week (e.g., weekday vs. weekend). \
             Please be as accurate as possible and do not simply multiply your \
             estimate for one day by 7.</p>",
  html:"<p style='text-align:left'>How old are you? <br> \
             <input required name='age' type='number'></p> \
        <p style='text-align:left'>With how many people do you converse orally \
        in a typical week? (Please only include people with whom you regularly \
        talk for longer than 5 minutes)<br> \
             <input required name='n_speak_to' type='number'></p> \
        <p style='text-align:left'>How many hours do you usually spend on \
        conversing orally with people in a typical week?<br>\
             <input required name='hours_speak_to' type='number'></p>"

Picture selection trials

Remember that on each picture selection trial the participant hears a description (“the fresh dill” etc) and the clicks on one of two images. We can do this fairly straightforwardly using the audio-button-response plugin (here is the documentation): we specify a stimulus which is the audio file we want to play, and then we can make the buttons be images rather than text; you have seen buttons several times already, but never with images, so that involves something a bit new.

You will notice that the directory for this experiment contains folders called picture_selection_sounds and picture_selection_images. Those contains all the sound files and images we should need. My example code just uses a few of these, but you can look at the full list of stimuli to see the full list of what images and sounds are available and how they fit together. The important things at this point are:

So what we want to do on each picture selection trial is play the sound file and show two buttons with the pair of images. We’ll start off doing this without images and with text buttons instead, and gradually build up to the implementation that’s in the code.

Forgetting about images for a moment, we could build a simple selection task like this:

var dill_trial = {type:'audio-button-response',

That would play the sound file picture_selection_sounds/fresh_dill.mp3 (note that we have to tell the code that this sound file can be found in the folder picture_selection_sounds), and give the participant two text-button options, “fresh_dill” and “dry_dill” (so no images yet). The order of those choices is fixed though - the target is on the left - and unless we want to manually randomise when constructing our trial list it might be wise to borrow some of the tricks from the word learning experiment and randomise the order of the buttons on every trial. As usual, the jsPsych plugin won’t record this for us, so we will have to use the data object again to keep track of what order the buttons are in and which one the participant clicked on. We can just borrow the code from the word learning experiment to do this:

var dill_trial = {type:'audio-button-response',
                  on_start: function(trial) {
                      var shuffled_label_choices = jsPsych.randomization.shuffle(trial.choices)
                      trial.choices = shuffled_label_choices
                      trial.data = {button_choices:shuffled_label_choices}

                   //at the end, use data.button_pressed to figure out
                   //which label they selected, and add that to data
                   on_finish: function(data) {
                      var button_number = data.button_pressed
                      data.button_selected = data.button_choices[button_number]

So we initially specify the default ordering of the choices as ["fresh_dill","dry_dill"], then in on_start we randomise that order, set choices to the new randomised order and then make a note in data of that randomised order, under the heading button_choices. Then in on_finish (i.e. after the participant has pressed a button) we use the button_pressed information recorded automatically to work out which choice the participant selected, and store that in data as button_selected. By this point button_ is getting quite overloaded - there’s button_pressed which is the button index recorded by the plugin, button_choices which is our list of choices, and button_selected which is the choice corresponding to the button index the participant clicked. If you find that confusing you could call button_choices and/or button_selected something different - those names are somewhat arbitrary, I could have gone with a different name.

At this point we are getting close to what we want - play a sound file, click on a button, with the button position randomised - but of course our buttons just have the text “fresh_dill” and “dry_dill” in them, and actually we want the images from the corresponding image files. One way to do that is to replace our simple text button choices with <img ...> tags, which tell the browser to show an image rather than some text. For instance, this would work:

var dill_trial = {type:'audio-button-response',
                  choices:["<img src=picture_selection_images/fresh_dill.jpg width=250px>",
                          "<img src=picture_selection_images/dry_dill.jpg width=250px>"]

(with … meaning everything else the same as the earlier example). We use the img tag to make the browser include an image, and then use src to tell it where to get the image from (note that we include the directory name, picture_selection_images, and the image type, .jpg). We also tell it how big we want the image to be - in this case, telling it to display the image at 250 pixels width. Then everything else will work as before, the two buttons will be shuffled, and we’ll end up with clickable image buttons. The only downside is that this is quite redundant - for both buttons we specify exactly the same information about the file path, the width etc, which seems kind of inefficient and potentially error prone. Also, all that button formatting stuff will be saved in data and eventually added to our experiment data, which is a bit messy and will make our data hard to look at.

There is actually a way around this, which is to use the button_html parameter of the plugin, which allows us to specify how all the buttons should be shown. I used this briefly in the word learning experiment for the invisible buttons, but we can use it here too to specify that the choices should be used as part of the name for image files when building the buttons. Integrating this into the code (with … meaning everything else the same as the earlier example):

var dill_trial = {type:'audio-button-response',
                  button_html: '<button class="jspsych-btn"> <img src="picture_selection_images/%choice%.jpg" width=250px></button>',


What that extra bit of code in button_html does is set up a template for the buttons that the information in choices is slotted into (the marker %choice% tells the code where to drop in the information from choices) - so it will use “fresh_dill” as (part of) the file name for one button, “dry_dill” for the other. Then I only specify all the button formatting once, and also in my data I am just going to end up recording the important varying information (the image name, rather than the full path and all the button format stuff), which makes my experiment data less awful to look at.

We are nearly done, but of course this is just the specification for one trial, and we are going to need to specify many trials - they will all have the same format and just differ in stimulus and choices, so I really don’t want to write them all out in long format when building my trial list. One way around this is to use a fairly simple nested timeline as we have done in previous weeks, where we make an audio-button-response trial that specifies the common proporties of all these trials and give it a nested timeline with the information that varies per trial:

var selection_stim_list = [{stimulus:"picture_selection_sounds/fresh_dill.mp3",

var selection_trials = {type:'audio-button-response',
                        button_html: '<button class="jspsych-btn"> <img src="picture_selection_images/%choice%.jpg" width=250px></button>',
                        on_start: function(trial) {
                            var shuffled_label_choices = jsPsych.randomization.shuffle(trial.choices)
                            trial.choices = shuffled_label_choices
                            trial.data = {button_choices:shuffled_label_choices}
                         on_finish: function(data) {
                            var button_number = data.button_pressed
                            data.button_selected = data.button_choices[button_number]}

That is a bit better - I specify my selection_stim_list, which is just a list of stimulus and choices for my block of trials, then I use that as my embedded timeline. But I am still not quite satisfied, because laying out the selection_stim_list still looks a bit complicated - each object in that list is quite complicated, and it’s hard for me to look at that and see exactly what is going on. Remember that I am just going to give a slightly different sound file name for manipulated or non-manipulated sound files, and I will have to change all that in this list - making sure I have done it properly and have exactly the trials I want looks like it might be awkward. So instead I am going to write a little function that I can use to build selection_stim_list for me - I specify what I want the trial to look like at a high level (what is the sound file, is it the manipulated sound file or not, and what the the two buttons going to show?) and it will generate the correct stimulus and choices for me. Here’s my function:

function make_image_selection_stimulus(sound,manipulated,target_image,foil_image) {
  if (manipulated) {
    //manipulated files have "_man" (for manipulated) stuck on the end of the file name
    var sound_file = "picture_selection_sounds/" + sound + "_man.mp3"
  else {
    var sound_file = "picture_selection_sounds/" + sound + ".mp3"
  var stim = {stimulus:sound_file,
  return stim

sound is the name of the sound file (minus all the path info etc - the code will add that for me), manipulated is either true (use the 24ms VOT version) or false (use the normal version), and target_image and foil_image are the names of the target and foil picture (again, minus any path info). The function doesn’t do anything fancy, and mainly just bundles this information we pass in into the correct format and returns that - however, it builds the full sound file name for us, and based on the value of manipulated it will either include “_man” at the end of the file name or not (remember, files with “_man” on the end are the manipulated audio versions).

Here is how I use it to build my selection_stim_list:

var selection_stim_list = [make_image_selection_stimulus("fresh_dill",true,"fresh_dill","dry_dill"),

Now I feel much happier about my procedure for building my picture selection trial list. It’s nice and clear to me what the sound and images are going to be. And it’s nice and clear if it’s a manipulated-audio trial or not - in this case I have manipulated audio for the /d/ trial but not for the /t/ trial and not for the filler trials (NB: there are no manipulated audio files for the fillers, so if you try that it will complain that it can’t find those files).

Then I can plug that selection_stim_list into my picture selection trial as a nested timeline. I am also going to add 3 things to my picture selection trials, which I will explain once I show you the code.

var selection_trials = {type:'audio-button-response',
                        timeline: jsPsych.randomization.shuffle(selection_stim_list), //shuffle
                        button_html: '<button class="jspsych-btn"> <img src="picture_selection_images/%choice%.jpg" width=250px></button>',
                        post_trial_gap: 500, //a little pause between trials
                        on_start: function(trial) {
                            var shuffled_label_choices = jsPsych.randomization.shuffle(trial.choices)
                            trial.choices = shuffled_label_choices
                            trial.data = {button_choices:shuffled_label_choices}
                         on_finish: function(data) {
                            var button_number = data.button_pressed
                            data.button_selected = data.button_choices[button_number]
                            savePerceptualLearningDataLine(data) //save the trial data

This is the same trial structure as before (i.e the nested timeline, the button_html, the on_start and on_end functions), but with 3 additions:

That’s it for the picture selection phase of this experiment, which is the most complex part.

Phoneme categorization trials

This will be relatively simple. Remember that in each phoneme categorization trial the participant hears a voice (either the same speaker as in the picture selection phase or a new [male] speaker) and indicates by button press if that word is “dean” or “teen” (i.e. whether it started with a /d/ or a /t/); we can do all this using the audio-button-response plugin. We can use essentially exactly the same approach as above, except that we always present the same two choices on each trial (dean vs teen). Here’s the code:

var categorization_stim_list = [{stimulus:'phoneme_categorization_sounds/samespeaker_VOT5.mp3'},

var categorization_trials = {type:'audio-button-response',
                              post_trial_gap: 500,
                              on_start: function(trial) {
                                  trial.data = {button_choices:trial.choices}
                              on_finish: function(data) {
                                var button_number = data.button_pressed
                                data.button_selected = data.button_choices[button_number]

A few things to note:

Saving data trial by trial

The rest of the code sets up the timeline in the usual way (creating placeholders for the instruction screens, using cocat to concatenate the various lists of trials, then jsPsych.init to run the timeline). The only interesting new thing is the function savePerceptualLearningDataLine which we call each time a critical trial (picture selection or phoneme categorization) finishes. We pass this function the trial’s data, and it digs out the data we want, uses join to stick together that list of data into a comma-separated string, and then uses the saveData function that we introduced last week to write that data to a file called perceptuallearning_data.csv. Since saveData appends to the end of the file, each new line of data will be added, rather than over-writing the previous contents of the file. If you downloaded a new version of save_data.php you will have to make sure the path to the server_data directory is correct, i.e. make sure it contains your UUN rather than mine!

function savePerceptualLearningDataLine(data) {
    // choose the data we want to save - this will also determine the order of the columns
    var data_to_save = [
    // join these with commas and add a newline
    var line = data_to_save.join(',')+"\n";
    saveData('perceptuallearning_data.csv', line);

One shortcoming of this method is that our csv file won’t have column names, which is not ideal - you could however write them in the same way, doing something like this before you start the experiment timeline:

saveData('perceptuallearning_data.csv', "trial_index,time_elapsed,stimulus,button_choice_1,button_choice_2,button_selected,

That just uses the saveData function to write a string to the file, where that string is the names of all the columns, comma-separated. I haven’t put this in the code but you could if you want.

A note on preloading images

You might notice that when you run through the experiment the images in the buttons take a moment to load at the start of each trial. jsPsych is set up to preload as much stuff as it can - on audio-button-response trials it preloads the audio specified in the stimulus parameter, on image-button-response trials it preloads the image stimulus. But it doesn’t automatically preload our button images, because they don’t appear in a place it expects to have to preload. It is actually possible to tell jsPsych to preload extra stimuli, which you can do in jsPsych.init (see the jsPsych documentation for other stuff you can do at initialisation). The way to do this would be to build a list of images that you use in the buttons, then preload those, e.g. like this:

var all_button_images = ["picture_selection_images/fresh_dill.jpg",

    preload_images: all_button_images,
    timeline: full_timeline,
    on_finish: function(){
      jsPsych.data.displayData('csv') //and also dump *all* the data to screen

That is a little bit unsatisfactory because we are manually building the list of images to preload. We could extract this automatically from selection_stim_list, e.g. using a for-loop to work through selection_stim_list and extract the image names from choices and add them to a preload list, but this code is already long enough for one week so I will leave that as an optional exercise for the keen!

Exercises with the perceptual learning experiment code

Attempt these problems.


Lev-Ari, S. (2017). Talking to fewer people leads to having more malleable linguistic representations. PLoS ONE, 12, e0183593.


All aspects of this work are licensed under a Creative Commons Attribution 4.0 International License.

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