An example of how to code this up
In the week 6 practical I set the following problem - note that it’s marked as optional and challenging, although once you have seen it done once it’s actually fairly simple.
jsPsych.randomization.shuffleNoRepeats function documented here to do a version where observation and test trials for multiple objects are interspersed, but you never see the same object twice in a row? NB this will only work if you have 3+ different objects in the experiment - it’s too hard for the code to find randomisations with no repeats if you have a small number of objects, and impossible if you only have one object, so the code will hang while endlessly searching!The first thing to do is check out the documentation for the jsPsych.randomization.shuffleNoRepeats function, where you’ll see that that function takes two arguments - a list (in our case, a list of trials) to be shuffled, and then an equality test, a function that examines pairs of items in that list and tells you whether or not two items from the list constitute repeats. There’s also a little example in the documentation of how to do this, which turns out to be very helpful.
You can download my code through the following two links:
If you drop these into your word_learning folder they will be able to access the images folder that’s already there.
There’s nothing clever going on in the html file - it’s just loading the required jsPsych plugins and the javascript file - so open the word_learning_norepeat.js file and take a look at how it works. If you work through that, you’ll see that the functions for making observation and production trials are unchanged. The first difference from the basic code includes a bunch of lines to expand the observation and production tests from a single object to 3 objects - as per my instructions, you need 2+ objects to shuffle the list such that the same object never repeats on consecutive trials, and in practice you need 3+ objects to give the code a chance to find a valid shuffle, so I went for 3 objects.
var observation_trial_object4_buv = make_observation_trial("object4", "buv");
var observation_trial_object4_cal = make_observation_trial("object4", "cal");
var observation_trial_object5_seb = make_observation_trial("object5", "seb");
var observation_trial_object5_nuk = make_observation_trial("object5", "nuk");
//zero variation for this one, just for fun
var observation_trial_object6_dap = make_observation_trial("object6", "dap");
//stick them all together and generate the repeats in a single step
var observation_trials = jsPsych.randomization.repeat(
[
observation_trial_object4_buv,
observation_trial_object4_cal,
observation_trial_object5_seb,
observation_trial_object5_nuk,
observation_trial_object6_dap,
],
[3, 2, 4, 1, 5]
);
You can see I am just doing the same thing as I did in the basic code for a single-object version of the experiment, but bringing in extra object images, extra labels (which I got from the paper) and using jsPsych.randomization.repeat to make multiple copies of those trials (3 copies of object4 + buv, 2 copies of object4 + cal, 4 copies of object5 + seb, 1 copy of object5 + nuk, 5 copies of object6 + dap).
observation_trials will include the stuff I want but in fully random order - so it will probably have direct repeats of the same object twice in a row. So I need to shuffle this again to avoid the same object repeating on consecutive trials. I can do that using the jsPsych.randomization.shuffleNoRepeats function, but I need to tell it what counts as a repeated trial (so it can shuffle to avoid those). I want to avoid having the same object on consecutive trials, and I know that the object shown on a given trial will be contained in that trial’s stimulus parameter. So I need to write a function that says “two trials count as a repeat if they both have the same stimulus parameter”. Luckily this is very very close to the example in the jsPsych documentation, which involves shuffling a list and avoiding two entries with the same colour value, so I can adapt that pretty straightforwardly.
There are two ways I can create my equality test function. I could create a named function that takes two trials and checks if they have the same stimulus, like this:
function my_equality_test(trial1, trial2) {
return trial1.stimulus == trial2.stimulus;
}
So that’s a function that takes 2 trials, looks up their stimulus parameter, and then returns the comparison of those two parameters (NB I am using == to test if they are the same, which is crucially different from the assignment operator, =!!!). If the stimulus is the same this function will return true (i.e. these two trials constitute a repeat), otherwise it’ll return false. We could then use that to shuffle our observation trials, like this:
var observation_trials_norepeats = jsPsych.randomization.shuffleNoRepeats(
observation_trials,
my_equality_test
);
That tells the shuffle function to use the my_equality_test function to test for repeats while shuffling observation_trials, so it will generate a trial list without any such repeats.
The way they do it in the jsPsych documentation is actually slightly different, using what’s known as an anonymous function - this is just a slightly more compact way of creating a temporary nameless function exactly where we need it (i.e. inside the call to jsPsych.randomization.shuffleNoRepeats). I have gone for that option in my example code, it looks like this:
var observation_trials_norepeats = jsPsych.randomization.shuffleNoRepeats(
observation_trials,
function (trial1, trial2) {
return trial1.stimulus == trial2.stimulus;
}
);
function(trial1,trial2) {...} creates an anonymous function that takes 2 trials and tests for the quality of the stimulus parameter as before - you can see that the code for this anonymous function is virtually identical to the code for my_equality_test, but now it’s all done inside the call to jsPsych.randomization.shuffleNoRepeats - we just put the function where it’s needed and don’t bother naming it. Either of these options is fine, and if you find the version using the named function less confusing, use that!
So that’s how we create observation_trials, our list of shuffled trials with no consecutive occurrences of the same object. You can see that on lines 97-98 of my code I am using console.log to show the unshuffled and shuffled trial lists in the console, so you can view those there and see if you can see the difference. Then in the rest of the code I use exactly the same process (once again involving an anonymous function) to shuffle the production trials; again, I console log those so you can look at the unshuffled and shuffled lists in the console.
If that was too easy for you, a slightly harder option would be to try to shuffle the observation trials so that the same object can occur on consecutive trials, but you never see the same label twice in a row. To figure out how to do that, you might want to look at the console-logged trial lists and think about how you can retrieve the info you need from those in order to test for the relevant equality.
All aspects of this work are licensed under a Creative Commons Attribution 4.0 International License.