randomise left/right position of buttons

[mw719]

Hi,

I'm still a beginner in jsPsych. Does anyone know how to randomise button positions (left/right) with the html-button-response plugin? I just couldn't get it work.

Thank you very much in advance!

[jodeleeuw]

Hi @mw719 ,

The button order is determined by the order in the choices array, so you can shuffle() the array to get a random order.

var trial = {
	type: 'html-button-response',
	stimulus: 'Pick one.',
	choices: jsPsych.randomization.shuffle(['Option One', 'Option Two'])
}

The trouble with this is that you need to know the button order to know which one was pressed. You can solve this by saving the button order in the trial's data like this:

var trial = {
	type: 'html-button-response',
	stimulus: 'Pick one.',
	choices: jsPsych.randomization.shuffle(['Option One', 'Option Two']),
	on_start: function(params){
		params.data.button_order = JSON.stringify(params.choices);
	}
}

The above method uses the on_start event to access the choices parameter and save it into the data parameter.

You could then save the label of the button clicked in the data when the trial finishes:

var trial = {
	type: 'html-button-response',
	stimulus: 'Pick one.',
	choices: jsPsych.randomization.shuffle(['Option One', 'Option Two']),
	on_start: function(params){
		params.data.button_order = JSON.stringify(params.choices);
	},
	on_finish: function(data){
		var button_order = JSON.parse(data.button_order);
		data.button_pressed_label = button_order[data.button_pressed]
	}
}

[mw719]

Hi @jodeleeuw,

thanks a lot for you help! This code interpreted my choice variables as the trials, but I wanted to have other variables (a whole list) to be randomised. When implementing jsPsych.randomization.shuffle() below on_start, it worked. Thank you so much again! One last question: what is exactly the meaning of JSON.stringify and JSON.parse? Aren't the button presses saved without it as well?

[jodeleeuw]

JSON.stringify() converts the array to a string representation of the array. JSON.parse() reverts the string back to the array. It's considered best practice in the current version of jsPsych to only store "primitive" data types in the data. So whenever we need to save objects or arrays we save them as their JSON-encoded string instead.

[mw719]

okay, that makes sense! Thank you so much for your help, @jodeleeuw! :)