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image-keyboard-response

Current version: 2.2.0. See version history.

This plugin displays an image 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 participant has failed to respond within a fixed length of time.

Image files can be automatically preloaded by jsPsych using the preload plugin. However, if you are using timeline variables or another dynamic method to specify the image stimulus, you will need to manually preload the images.

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 string undefined The path of the image file to be displayed.
stimulus_height integer null Set the height of the image in pixels. If left null (no value specified), then the image will display at its natural height.
stimulus_width integer null Set the width of the image in pixels. If left null (no value specified), then the image will display at its natural width.
maintain_aspect_ratio boolean true If setting only the width or only the height and this parameter is true, then the other dimension will be scaled to maintain the image's aspect ratio.
choices array of strings "ALL_KEYS" This array contains the key(s) that the participant is allowed to press in order to respond to the stimulus. Keys should be specified as characters (e.g., 'a', 'q', ' ', 'Enter', 'ArrowDown') - see this page and this page (event.key column) for more examples. Any key presses that are not listed in the array will be ignored. The default value of "ALL_KEYS" means that all keys will be accepted as valid responses. Specifying "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 participant is supposed to take (e.g., which key to press).
stimulus_duration numeric null How long to show the stimulus for in milliseconds. If the value is null, then the stimulus will be shown until the participant makes a response.
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, then the trial will wait for a response indefinitely.
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 set this parameter to false to force the participant to view a stimulus for a fixed amount of time, even if they respond before the time is complete.
render_on_canvas boolean true If true, the image will be drawn onto a canvas element. This prevents a blank screen (white flash) between consecutive image trials in some browsers, like Firefox and Edge. If false, the image will be shown via an img element, as in previous versions of jsPsych. If the stimulus is an animated gif, you must set this parameter to false, because the canvas rendering method will only present static images.
wait_for_key_release boolean false If true, the response is not registered until the participant releases the key. The response time (rt) still reflects when the key was pressed, and the additional data field rt_key_duration records how long the key was held down. Note that when this is true, the trial cannot end until the key is released: with response_ends_trial: true the trial ends at the key release, and if the trial ends for another reason (e.g., trial_duration) while the key is still held, no response is recorded for the trial.

Data Generated

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

Name Type Value
response string Indicates which key the participant pressed.
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.
stimulus string The path of the image that was displayed.
rt_key_duration numeric The duration in milliseconds that the response key was held down, measured from key press to key release. Only recorded when wait_for_key_release is true; null otherwise or when no response was made.

Install

Using the CDN-hosted JavaScript file:

<script src="https://unpkg.com/@jspsych/plugin-image-keyboard-response@2.2.0"></script>

Using the JavaScript file downloaded from a GitHub release dist archive:

<script src="jspsych/plugin-image-keyboard-response.js"></script>

Using NPM:

npm install @jspsych/plugin-image-keyboard-response

import imageKeyboardResponse from '@jspsych/plugin-image-keyboard-response';

Examples

Displaying trial until participant gives a response 
var trial = {
    type: jsPsychImageKeyboardResponse,
    stimulus: 'img/happy_face_1.png',
    choices: ['e', 'i'],
    prompt: "<p>Is this person happy or sad? Press <kbd>e</kbd> for happy and <kbd>i</kbd> for sad.</p>",
};

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Displaying image for a fixed duration; no response allowed 
var trial = {
    type: jsPsychImageKeyboardResponse,
    stimulus: 'img/happy_face_1.png',
    choices: "NO_KEYS",
    prompt: "<p>Study this face for 5 seconds.</p>",
    trial_duration: 5000
};

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