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

jspsych-canvas-keyboard-response

This plugin can be used to draw an image on a JavaScript canvas element, which can be useful for displaying parametrically defined shapes, and records responses generated with the keyboard. 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.

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 keycodes	jsPsych.ALL_KEYS	This array contains the keys that the subject is allowed to press in order to respond to the stimulus. Keys can be specified as their numeric key code or as characters (e.g., 'a', 'q'). The default value of jsPsych.ALL_KEYS means that all keys will be accepted as valid responses. Specifying jsPsych.NO_KEYS will mean that no responses are allowed.
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).
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.
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, then the trial will wait for a response indefinitely.
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 timing_response parameter). If false, then the trial will continue until the value for trial_duration 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
key_press	numeric	Indicates which key the subject pressed. The value is the numeric key code corresponding to the subject's response.
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.
stimulus	function	The function that was drawn.

Examples

Displaying a drawing until subject gives a response

function drawRect(c){
    var ctx = c.getContext('2d');
    ctx.beginPath();
    ctx.rect(30, 30, 200, 50);
    ctx.stroke();
}

var trial = {
    type: 'canvas-keyboard-response',
    stimulus: drawRect,
    choices: ['e','i'],
    prompt: '<p>is this a circle or a rectangle? press "e" for circle and "i" for rectangle</p>',
}

Displaying a circle for 1 second, no response allowed

function drawCirc(c){
    var ctx = c.getContext('2d');
    ctx.beginPath();
    ctx.arc(100, 75, 50, 0, 2 * Math.PI);
    ctx.stroke();
}

var trial = {
    type: 'canvas-keyboard-response',
    stimulus: drawCirc,
    choices: jsPsych.NO_KEYS,
    trial_duration: 1000,
}