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video-keyboard-response

Current version: 1.1.2. See version history.

This plugin plays a video file and records a keyboard response. The stimulus can be displayed until a response is given, or for a pre-determined amount of time. The trial can be ended automatically when the participant responds, when the video file has finished playing, or if the participant has failed to respond within a fixed length of time. You can also prevent a keyboard response from being recorded before the video has finished playing.

Video 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 video stimulus, you will need to manually preload the videos. Also note that video preloading is disabled when the experiment is running as a file (i.e. opened directly in the browser, rather than through a server), in order to prevent CORS errors - see the section on Running Experiments for more information.

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 array undefined An array of file paths to the video. You can specify multiple formats of the same video (e.g., .mp4, .ogg, .webm) to maximize the cross-browser compatibility. Usually .mp4 is a safe cross-browser option. The plugin does not reliably support .mov files. The player will use the first source file in the array that is compatible with the browser, so specify the files in order of preference.
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).
width numeric width of the video file The width of the video display in pixels.
height numeric heigh of the video file The height of the video display in pixels.
autoplay boolean true If true, the video will begin playing as soon as it has loaded.
controls boolean false If true, controls for the video player will be available to the participant. They will be able to pause the video or move the playback to any point in the video.
start numeric null If given a value, the video will start at this time point in seconds.
stop numeric null If given a value, the video will stop at this time point in seconds.
rate numeric null The playback rate of the video. 1 is normal, <1 is slower, >1 is faster.
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.
trial_ends_after_video bool false If true, then the trial will end as soon as the video file finishes playing.
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.
response_allowed_while_playing boolean true If true, then responses are allowed while the video is playing. If false, then the video must finish playing before a keyboard response is accepted. Once the video has played all the way through, a valid keyboard response is allowed (including while the video is being re-played via on-screen playback controls).

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 array The stimulus array. This will be encoded as a JSON string when data is saved using the .json() or .csv() functions.

Simulation Mode

In data-only simulation mode, the response_allowed_while_playing parameter does not currently influence the simulated response time. This is because the audio file is not loaded in data-only mode and therefore the length is unknown. This may change in a future version as we improve the simulation modes.

Install

Using the CDN-hosted JavaScript file:

<script src="https://unpkg.com/@jspsych/plugin-video-keyboard-response@1.1.2"></script>

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

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

Using NPM:

npm install @jspsych/plugin-video-keyboard-response
import videoKeyboardResponse from '@jspsych/plugin-video-keyboard-response';

Examples

Show a video and advance to next trial automatically
var trial = {
  type: jsPsychVideoKeyboardResponse,
  stimulus: [
    'video/fish.mp4'
  ],
  choices: "NO_KEYS",
  trial_ends_after_video: true
};

Stock Footage provided by rjt98, from Pond5

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