canvas-button-response¶
Current version: 2.0.0. See version history.
This plugin can be used to draw a stimulus on a HTML canvas element, and record a button click response and response time. The canvas stimulus can be useful for displaying dynamic, parametrically-defined graphics, and for controlling the positioning of multiple graphical elements (shapes, text, images). 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 participant has failed to respond within a fixed length of time. One or more button choices will be displayed under the canvas, and the button style can be customized using HTML formatting.
Parameters¶
In addition to the parameters available in all plugins, this plugin accepts the following 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 automatically takes a canvas element as its only argument, e.g. function(c) {...} or function drawStim(c) {...}, where c refers to the canvas element. Note that the stimulus 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] | Array that defines the size of the canvas element in pixels. First value is height, second value is width. |
| choices | array of strings | [] | Labels for the buttons. Each different string in the array will generate a different button. |
| button_html | function | (choice: string, choice_index: number)=>`<button class="jspsych-btn">${choice}</button>; |
A function that generates the HTML for each button in the choices array. The function gets the string and index of the item in the choices array and should return valid HTML. If you want to use different markup for each button, you can do that by using a conditional on either parameter. The default parameter returns a button element with the text label of the choice. |
| 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 participant is supposed to take (e.g., what question to answer). |
| trial_duration | numeric | null | How long to wait for the participant to make a response before ending the trial in milliseconds. If the participant fails to make a response before this timer is reached, the participant'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. |
| button_layout | string | 'grid' | Setting to 'grid' will make the container element have the CSS property display: grid and enable the use of grid_rows and grid_columns. Setting to 'flex' will make the container element have the CSS property display: flex. You can customize how the buttons are laid out by adding inline CSS in the button_html parameter. |
| grid_rows | number | 1 | The number of rows in the button grid. Only applicable when button_layout is set to 'grid'. If null, the number of rows will be determined automatically based on the number of buttons and the number of columns. |
| grid_columns | number | null | The number of columns in the button grid. Only applicable when button_layout is set to 'grid'. If null, the number of columns will be determined automatically based on the number of buttons and the number of rows. |
| response_ends_trial | boolean | true | If true, then the trial will end whenever the participant 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 trial_duration is reached. You can use this parameter to force the participant 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 participant to make a response. The time is measured from when the stimulus first appears on the screen until the participant's response. |
| response | numeric | Indicates which button the participant pressed. The first button in the choices array is 0, the second is 1, and so on. |
Note: the canvas stimulus is not included in the trial data because it is a function. Any stimulus information that should be saved in the trial data can be added via the data parameter.
Install¶
Using the CDN-hosted JavaScript file:
<script src="https://unpkg.com/@jspsych/plugin-canvas-button-response@2.0.0"></script>
Using the JavaScript file downloaded from a GitHub release dist archive:
<script src="jspsych/plugin-canvas-button-response.js"></script>
Using NPM:
npm install @jspsych/plugin-canvas-button-response
import canvasButtonResponse from '@jspsych/plugin-canvas-button-response';
Examples¶
Drawing circles based on parameters
function filledCirc(canvas, radius, color) {
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.arc(150, 150, radius, 0, 2 * Math.PI);
ctx.fillStyle = color;
ctx.fill();
}
var circle_1 = {
type: jsPsychCanvasButtonResponse,
stimulus: function(c) {
filledCirc(c, 100, 'blue');
},
canvas_size: [300, 300],
choices: ['Red', 'Green', 'Blue'],
prompt: '<p>What color is the circle?</p>',
data: {color: 'blue', radius: 100}
};
var circle_2 = {
type: jsPsychCanvasButtonResponse,
stimulus: function(c) {
filledCirc(c, 150, 'green');
},
canvas_size: [300, 300],
choices: ['Larger', 'Smaller'],
stimulus_duration: 1000,
prompt: '<p>Is this circle larger or smaller than the last one?</p>'+
'<p>Stimulus will be hidden after 1 second.</p>',
data: {color: 'green', radius: 150}
};
Using an anonymous stimulus function
var lines = {
type: jsPsychCanvasButtonResponse,
stimulus: function(c) {
var ctx = c.getContext("2d");
// first line
ctx.beginPath();
ctx.moveTo(200, 10);
ctx.lineTo(200, 250);
ctx.lineWidth = 10;
ctx.strokeStyle = 'MediumBlue';
ctx.stroke();
// second line
ctx.beginPath();
ctx.moveTo(20, 100);
ctx.lineTo(100, 250);
ctx.lineWidth = 10;
ctx.strokeStyle = 'MediumPurple';
ctx.stroke();
},
canvas_size: [300, 300],
choices: ['Blue line', 'Purple line'],
prompt: '<p>Which line is longer?</p>',
data: {line1_color: 'blue', line1_length: 290, line2_color: "purple", line2_length: 170}
};
Using the canvas stimulus function with timeline variables, and recording the correctness of responses
function filledCirc(canvas, radius, color) {
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.arc(150, 150, radius, 0, 2 * Math.PI);
ctx.fillStyle = color;
ctx.fill();
}
var circle_procedure = {
timeline: [
{
type: jsPsychCanvasButtonResponse,
stimulus: function(c) {
filledCirc(c, jsPsych.evaluateTimelineVariable('radius'), jsPsych.evaluateTimelineVariable('color'));
},
canvas_size: [300, 300],
choices: ['Red', 'Green', 'Blue'],
prompt: '<p>What color is the circle?</p>',
data: {
radius: jsPsych.timelineVariable('radius'),
color: jsPsych.timelineVariable('color'),
correct_response: jsPsych.timelineVariable('correct_response')
},
on_finish: function(data){
data.correct = data.response == data.correct_response;
}
}
],
timeline_variables: [
{radius: 80, color: 'red', correct_response: 0},
{radius: 100, color: 'green', correct_response: 1},
{radius: 50, color: 'blue', correct_response: 2}
],
randomize_order: true
};