image-keyboard-response

This plugin displays and 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 subject 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 subject 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 subject 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 subject makes a response.
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 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 subject 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.

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 subject pressed.
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	string	The path of the image that was displayed.

Examples

Displaying trial until subject gives a response

Code

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

Demo

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Displaying image for a fixed duration; no response allowed

Code

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
};

Demo

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