jsPsych/docs/plugins/jspsych-canvas-button-response.md

jspsych-canvas-button-response

This plugin can be used to draw a stimulus on a JavaScript canvas element, which can be useful for displaying parametrically defined shapes, and records responses generated by button click. The stimulus can be displayed until a response is given, or for a pre-determined amount of time. The trial can be ended automatically if the subject has failed to respond within a fixed length of time. The button itself can be customized using HTML formatting.

Parameters

Parameters with a default value of undefined must be specified. Other parameters can be left unspecified if the default value is acceptable.

Parameter	Type	Default Value	Description
stimulus	function	undefined	The function to draw on the canvas. This function must take a canvas element as its only argument, e.g. foo(c). Note that the function will still generally need to set the correct context itself, using a line like let ctx = c.getContext("2d").
canvas_size	array	[500, 500]	The size of the canvas element in pixels.
choices	array of strings	[]	Labels for the buttons. Each different string in the array will generate a different button.
button_html	HTML string	'<button class="jspsych-btn">%choice%</button>'	A template of HTML for generating the button elements. You can override this to create customized buttons of various kinds. The string %choice% will be changed to the corresponding element of the choices array. You may also specify an array of strings, if you need different HTML to render for each button. If you do specify an array, the choices array and this array must have the same length. The HTML from position 0 in the button_html array will be used to create the button for element 0 in the choices array, and so on.
prompt	string	null	This string can contain HTML markup. Any content here will be displayed below the stimulus. The intention is that it can be used to provide a reminder about the action the subject is supposed to take (e.g., which key to press).
trial_duration	numeric	null	How long to wait for the subject to make a response before ending the trial in milliseconds. If the subject fails to make a response before this timer is reached, the subject's response will be recorded as null for the trial and the trial will end. If the value of this parameter is null, the trial will wait for a response indefinitely.
stimulus_duration	numeric	null	How long to display the stimulus in milliseconds. The visibility CSS property of the stimulus will be set to hidden after this time has elapsed. If this is null, then the stimulus will remain visible until the trial ends.
margin_vertical	string	'0px'	Vertical margin of the button(s).
margin_horizontal	string	'8px'	Horizontal margin of the button(s).
response_ends_trial	boolean	true	If true, then the trial will end whenever the subject makes a response (assuming they make their response before the cutoff specified by the trial_duration parameter). If false, then the trial will continue until the value for timing_response is reached. You can use this parameter to force the subject to view a stimulus for a fixed amount of time, even if they respond before the time is complete.

Data Generated

In addition to the default data collected by all plugins, this plugin collects the following data for each trial.

Name	Type	Value
rt	numeric	The response time in milliseconds for the subject to make a response. The time is measured from when the stimulus first appears on the screen until the subject's response.
button_pressed	numeric	Indicates which button the subject pressed. The first button in the choices array is 0, the second is 1, and so on
stimulus	function	The function that was drawn

Examples

Displaying question until subject gives a response

function filledCirc(canvas, color){
    ctx = canvas.getContext("2d");
    ctx.beginPath();
    ctx.arc(250, 250, 100, 0, 2 * Math.PI);
    ctx.fillStyle = color;
    ctx.fill()
}

var trial = {
    type: 'canvas-button-response',
    stimulus: function(c){ filledCirc(c, 'blue') },
    choices: ['red','green','blue'],
    prompt: '<p>What color is the circle?</p>',
}