jspsych-xab plugin

The XAB plugin displays either an image or HTML object stimulus (X). After a short gap, the plugin displays two additional stimuli (A and B). The subject selects which of the two stimuli matches X using the keyboard.

Parameters

This table lists the parameters associated with this plugin. 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
stimuli array undefined Array of two or three elements. If it is two elements, then the plugin will show the first element as X and as the target during the A/B portion (the second element will be the foil). If it is three elements, then the first is X the second is the target (A) and the third is the foil (B). This is useful if X and A are not identical, but A is still the correct choice (e.g. a categorization experiment where the goal is to pick the item that is in the same category). Stimuli can be paths to images, or html strings.
is_html boolean false If the elements of the stimuli array are strings containing HTML content, then this parameter must be set to true.
left_key numeric or string 'Q' Which key the subject should press to indicate that the target is on the left side.
right_key numeric or string 'P' Which key the subject should press to indicate that the target is on the right side.
prompt string "" 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).
timing_x numeric 1000 How long to show the X stimulus for in milliseconds.
timing_xab_gap numeric 1000 How long to show a blank screen in between X and AB in milliseconds.
timing_ab numeric -1 How long to show A and B in milliseconds. If the value of this parameter is -1, then the stimuli will remain on the screen until a response is given.
timing_response numeric -1 The maximum duration to wait for a response, measured from the onset of the AB portion of the trial. If -1, then the trial will wait indefinitely for a response.

Data Generated

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

Name Type Value
stimulus string JSON-encoded array of the stimuli used in the trial.
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 A and B stimuli first appear on the screen until the subject's response.
correct boolean True if the subject picks the correct answer.

Examples

Doing an exact match task

var block = {
    type: 'xab',
    stimuli: ['img/happy_face.png', 'img/sad_face.png'],
    prompt: "Press Q if the face you just saw is on the left. Press P if the face you just saw is on the right."
}

Matching based on a feature

var block = {
    type: 'xab',
    stimuli: ['img/happy_joe_face.png', 'img/sad_joe_face.png', 'img/sad_fred_face.png'],
    prompt: "Press Q if the person you just saw is on the left. Press P if the person you just saw is on the right."
}