Dive into the details of the experiment

The VAAST was created using jsPsych. The technology behind the experiment is 3 plugins: vaast-fixation, vaast-text and vaast-image, that you can find in the zip file.
These plugins make it possible for a participant to view a fixation cross for a random duration on a background screen. They also make the movement happen when a participant chooses to approach or avoid a stimulus.
These plugins have a few parameters that can allow you to customise your experiment. Let's see in more details:

We're using which plugin, where?

Please find below, multiple tables containing all the parameters of each plugin. Below each table, you will find examples of code for typical trials in the VAAST.

vaast-fixation plugin parameters

Parameter	Type	Default Value	Description
fixation	STRING	'+'	The string that is displayed as fixation.
font_size	INT	200	Font size of the fixations text.
min_duration	INT	800	Minimal duration (in ms).
max_duration	INT	2000	Maximal duration (in ms).
background_images	IMAGE	undefined	An array with the images displayed as background as function of the position.
position	INT	3	The position in the "background_images" array which will be used to set the background.

Examples of vaast-fixation trial

const vaast_fixation = {
  type: jsPsychVaastFixation,
  fixation: "+",
  font_size: 46,
  position: 1,
  background_images: background
}

vaast-image plugin parameters

Parameter	Type	Default Value	Description
stimulus	IMAGE	undefined	The image to be displayed.
approach_key	KEY	'Z'	The key press associated with an approach movement.
avoidance_key	KEY	'S'	The key press associated with an avoidance movement.
key_to_move_forward	KEYS	"ALL_KEYS"	This array contains the key(s) that the participant is allowed to press in order to advance to the next trial if their key press was incorrect. Keys should be specified as characters (e.g., `'a'`, `'q'`, `' '`, `'Enter'`, `'ArrowDown'`) - see {@link https://developer.mozilla.org/en-US/docs/Web/API/UI_Events/Keyboard_event_key_values this page} and {@link https://www.freecodecamp.org/news/javascript-keycode-list-keypress-event-key-codes/ 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.
display_feedback	BOOL	false	If true, then the code included in 'html_when_wrong' will be displayed when the user makes an incorrect key press.
feedback_duration	INT	null	How long the feedback is shown (in ms).
html_when_wrong	HTML_STRING	'X'	The content to display when a user presses the wrong key.
force_correct_key_press	BOOL	false	If true, the user will be forced to press the correct key in order to advance to the next trial after a wrong key press.
stim_movement	STRING	undefined	The movement associated with the stimulus (either "approach" or "avoidance").
font_sizes	INT	null	An array with the sizes of the string stimulus/ image as function of the position. The medium font corresponds to the stimulus font size when it's first presented. The smaller and larger fonts correspond to the stimulus font size when the movement is avoidance and approach, respectively.
response_ends_trial	BOOL	true	If true, the trial will end when the user makes a response. True in trials in which the participant responds to a stimulus. False in trials where the participant sees the position change on the screen (background and stimulus).
trial_duration	INT	null	How long to wait for the participant to make a response before ending the trial, in milliseconds. If the value of this parameter is `null`, then the trial will wait for a response indefinitely.
background_images	IMAGE	undefined	An array with the images displayed as background as function of the position.
position	INT	3	The position in the "background_images" array which will be used to set the background.

Example of vaast-image trial

First step of a trial

*You could also change force_correct_key_press to true to force the participants to respond correctly.

const vaast_first_step = {
type: jsPsychVaastImage,
stimulus: jsPsych.timelineVariable("stimulus"),
position: 1,
background_images: background,
font_sizes: image_sizes,
approach_key: "t",
avoidance_key: "b",
stim_movement: jsPsych.timelineVariable("movement"),
html_when_wrong: '<span style="color: red; font-size: 80px">×</span>',
force_correct_key_press: true,
display_feedback: true,
response_ends_trial: true,
};

Second step of a trial

const vaast_second_step = {
  type: jsPsychVaastImage,
  stimulus: jsPsych.timelineVariable("stimulus"),
  position: next_position_training,
  background_images: background,
  font_sizes: image_sizes,
  stim_movement: jsPsych.timelineVariable("movement"),
  response_ends_trial: false,
  trial_duration: 650,
};

Find more information on different possible trials on the tree below.

vaast-text plugin parameters

Parameter	Type	Default Value	Description
stimulus	STRING	undefined	The text to be displayed.
approach_key	KEY	'Z'	The key press associated with an approach movement.
avoidance_key	KEY	'S'	The key press associated with an avoidance movement.
key_to_move_forward	KEYS	"ALL_KEYS"	This array contains the key(s) that the participant is allowed to press in order to advance to the next trial if their key press was incorrect. Keys should be specified as characters (e.g., `'a'`, `'q'`, `' '`, `'Enter'`, `'ArrowDown'`) - see {@link https://developer.mozilla.org/en-US/docs/Web/API/UI_Events/Keyboard_event_key_values this page} and {@link https://www.freecodecamp.org/news/javascript-keycode-list-keypress-event-key-codes/ 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.
display_feedback	BOOL	false	If true, then the code included in 'html_when_wrong' will be displayed when the user makes an incorrect key press.
feedback_duration	INT	null	How long the feedback is shown (in ms).
html_when_wrong	HTML_STRING	'X'	The content to display when a user presses the wrong key.
force_correct_key_press	BOOL	false	If true, the user will be forced to press the correct key in order to advance to the next trial after a wrong key press.
stim_movement	STRING	undefined	The movement associated with the stimulus (either "approach" or "avoidance").
font_sizes	INT	null	An array with the sizes of the string stimulus/ image as function of the position. The medium font corresponds to the stimulus font size when it's first presented. The smaller and larger fonts correspond to the stimulus font size when the movement is avoidance and approach, respectively.
response_ends_trial	BOOL	true	If true, the trial will end when the user makes a response. True in trials in which the participant responds to a stimulus. False in trials where the participant sees the position change on the screen (background and stimulus).
trial_duration	INT	null	How long to wait for the participant to make a response before ending the trial, in milliseconds. If the value of this parameter is `null`, then the trial will wait for a response indefinitely.
background_images	IMAGE	undefined	An array with the images displayed as background as function of the position.
position	INT	3	The position in the "background_images" array which will be used to set the background.

Examples of vaast-text trial

First step of a test trial

const vaast_first_step = {
  type: jsPsychVaastText,
  stimulus: jsPsych.timelineVariable('stimulus'),
  position: 1,
  background_images: background,
  font_sizes: word_sizes,
  stim_movement: jsPsych.timelineVariable('movement'),
  approach_key:  approach_key,
  avoidance_key: avoidance_key,
  html_when_wrong: '<span style="color: red; font-size: 80px">×</span>',
  force_correct_key_press: false,
  display_feedback: false,
  response_ends_trial: true
}

Second step of a trial

const vaast_second_step = {
  type: jsPsychVaastText,
  position: next_position,
  stimulus: jsPsych.timelineVariable('stimulus'),
  background_images: background,
  font_sizes: word_sizes,
  stim_movement: jsPsych.timelineVariable('movement'),
  response_ends_trial: false,
  trial_duration: 500
}

First step of a training trial

*You could also change force_correct_key_press to true to force the participants to respond correctly.

const vaast_first_step_train = {
  type: jsPsychVaastText,
  stimulus: jsPsych.timelineVariable('stimulus'),
  position: 1,
  background_images: background,
  font_sizes: word_sizes,
  stim_movement: jsPsych.timelineVariable('movement'),
  approach_key:  approach_key,
  avoidance_key: avoidance_key,
  html_when_wrong: '<span style="color: red; font-size: 80px">×</span>',
  force_correct_key_press: false,
  display_feedback: true,
  feedback_duration: 500, 
  response_ends_trial: true
}

Find more information on different possible trials on the tree below.

A little tree to see more clearly

Note about a quick flash

Please note that a flash appears on the screen the first time a movement is made in either direction. Meaning, the first time the background image goes from center to closer and from center to further, there's a flash in the time bewteen the two images being shown. Note that it only happens once, as it probably has to do with the preloading of the images not working properly. Thus, if you choose not to use a training session (unlike we do), the first experimental trials might be slightly different from the next ones.