# jspsych-html-button-response

This plugin displays an image and records responses generated with a button click.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. The button itself can be customized using 
HTML formatting.

## 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
----------|------|---------------|------------
stimulus | string | undefined | The path of the image file to be displayed.
choices | Array of strings | [] | The button labels.
button_html | HTML string | `'<button class="jspsych-btn">%choice%</button>'` | A template of HTML for generating the button elements. You can override this to create customized buttons of various kinds. The string `%choice%` will be changed to the corresponding element of the `choices` array. You may also specify an array of strings, if you need different HTML to render for each button. If you do specify an array, the `choices` array and this array must have the same length. The HTML from position 0 in the `button_html` array will be used to create the button for element 0 in the `choices` array, and so on.
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).
trial_duration | numeric | -1 | 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 -1 for the trial and the trial will end. If the value of this parameter is -1, the trial will wait for a response indefinitely.
margin_vertical | String | '0px' | Vertical margin of the button.
margin_horizontal | String | '8px' | Horizontal margin of button.
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 `timing_response` 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.
trial_ends_after_audio | Boolean | false | If true, then the trial will end as soon as the audio file finishes playing.

## Data Generated

In addition to the [default data collected by all plugins](overview#datacollectedbyplugins), this plugin collects the following data for each trial.

Name | Type | Value
-----|------|------
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.
button_pressed | numeric | Indicates which button the subject pressed. The first button in the `choices` array is 0, the second is 1, and so on.

## Examples

#### Displaying question until subject gives a response

```javascript
var trial = {
	type: 'image-button-response',
	stimulus: 'img/happy_face_1.png',
	choices: ['Happy', 'Sad'],
	prompt: "<p>Is this person happy or sad?</p>"
};
```