Only the ‘stimuli’ parameter is required; Other parameters can be left unspecified if the default value is acceptable. Note that the prameter of choices, prompt, trial_duration, and response_ends_trial is the same as that of the plugins included in the jsPsych.
Main parameters
| Parameter |
Type |
Default Value |
Description |
| stimuli |
array |
undefined |
An array of objects, each object represents a stimulus to be presented in the trial. The properties (parameters) of each object are depend on the type of the object. See Stimulus parameters. |
| response_type |
string |
‘key’ |
How participants will respond. You can specify ‘key’, ‘mouse’, or ‘button’. |
| response_start_time |
numeric |
0 |
The defalut value (0) means that the participant can respond to the stimuli from the start of the trial, and the reaction time is the time from the start of the trial until the participant’s response. If the response_start_time is set to 1000, the participant can respond to the stimuli 1000 ms after from the start of the trial, and the reaction time is the time from 1000 ms after the start of the trial until the participant’s response. |
| 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 use this parameter to force the participant to view a stimulus for a fixed amount of time, even if they respond before the time is complete. |
| 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(s) to press). |
| upper_prompt |
string |
null |
This string can contain HTML markup. Any content here will be displayed above the canvas. |
| lower_prompt |
string |
null |
This is the same as prompt. Any content here will be displayed below the canvas. |
| 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, the trial will wait for a response indefinitely. |
stepFunc |
function |
null |
This can’t be used since v2.0. Please use the raf_func instead. |
| raf_func |
function |
null |
This function takes three arguments which are, in order, trial, elapsed time in terms of milliseconds. and elapsed time in terms of frames. This function is called by the requestAnimationFrame method, and excuted synchronized with the refresh of the display. Wnen you use the raf_func called by the requestAnimationFrame method, you have to specify the stimuli as an empty array. If you would like to draw stimuli using the canvas-drawing methods manually, the raf_func would be benefit. See, the raf_func.html and draw two images repeatedly.html. |
| Parameter |
Type |
Default Value |
Description |
| background_color |
string |
‘grey’ |
The background color of the canvas.The color can be specified using the HTML color names (e.g., 'black'), hexadecimal (HEX) colors (e.g., '#ff0000'), and RGB values (e.g., 'rgb(0, 255, 0)') that are often used in a general HTML file. |
| canvas_width |
numeric |
window.innerWidth |
The width of the canvas in which stimuli are drawn. If it is not specified, the width of the canvas is identical to that of the window. |
| canvas_height |
numeric |
window.innerHeight |
The height of the canvas in which stimuli are drawn. If it is not specified, the height of the canvas is identical to that of the window, but see the canvas_offsetY property. |
| canvas_offsetX |
numeric |
0 |
This value is subtracted from the width of the canvas in full-screen mode. However, since the default value is 0, it basically has no effect on the window size. |
| canvas_offsetY |
numeric |
8 |
This value is subtracted from the height of the canvas in full-screen mode to prevent the vertical scroll bar from being displayed. |
| clear_canvas |
boolean |
true |
If true, the canvas is cleared every frame. There are not many cases where this should be false, but if you want to draw the trajectory of the mouse, for example, you need to set it false. Note that in that case, the show_end_time property can not be used. See the mouse drawing.html |
| remain_canvas |
boolean |
false |
If true, the main canvas remains for the next trial. This is useful to present complex stimuli using multiple psychophysics objects. Note that this property doesn’t work with the Pixi mode. |
| Parameter |
Type |
Default Value |
Description |
| choices |
array of keycodes |
“ALL_KEYS” |
This array contains the keys that the participant is allowed to press in order to respond to the stimulus. Keys can be specified as their numeric key code or as characters (e.g., ‘a’, ‘q’). 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. |
The following parameters are enabled when the response_type is ‘button’.
| Parameter |
Type |
Default Value |
Description |
| mouse_down_func |
function |
null |
This is the event handler of the mousedown on the canvas. See the mouse_drawing.html and mouse_event.html. |
| mouse_up_func |
function |
null |
This is the event handler of the mouseup on the canvas. |
| mouse_move_func |
function |
null |
This is the event handler of the mousemove on the canvas. |
| key_down_func |
function |
null |
This is the event handler of the keydown on the document. See the keyboard_event.html. |
| key_up_func |
function |
null |
This is the event handler of the keyup on the canvas. |
| touchstart_func |
function |
null |
This is the event handler of the touchstart. See the touch events page on MDN Web Docs. |
| touchmove_func |
function |
null |
This is the event handler of the touchmove. |
| touchend_func |
function |
null |
This is the event handler of the touchend. |
| touchcancel_func |
function |
null |
This is the event handler of the touchcancel. |
Data Generated
In addition to the default data collected by all plugins, this plugin collects the following data for each trial.
| Name |
Type |
Value |
| rt |
numeric |
The response time in milliseconds for the participant to make a response. The start time of the measurement depends on the ‘response_start_time’. |
| response_type |
string |
‘key’, ‘mouse’, or ‘button’ |
| key_press |
string |
Indicates which key the participant pressed. ‘-1’ means thant the participant respond using a mouse. |
| response |
string or numeric |
If the response_type is ‘key’, this indicates which key the participant pressed, and is the same as the key_press. If the response_type is ‘button’, this indicates which button the subject pressed, and is the same as the button_pressed. If the response_type is ‘mouse’, this value is minus 1, and you should refer to the click_x and click_y properties instead. |
| avg_frame_time |
numeric |
Averaged interframe interval. |
| click_x/click_y |
numeric |
Horizontal/Vertical clicked position. The origin of the coordinate is the top left of the canvas, and the unit is the pixel. |
| center_x/center_y |
numeric |
Horizontal/Vertical position of the center of the window. The origin of the coordinate is the top left of the canvas, and the unit is the pixel. |
| 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. |
Read only parameters
From jsPsych V8, the following usage is no longer possible.
| Parameter |
Description |
canvas |
You can access the element of the canvas via the jsPsych.getCurrentTrial().canvas. |
context |
You can access the context of the canvas via the jsPsych.getCurrentTrial().context. |
centerX |
You can access the horizontal center of the canvas via the jsPsych.getCurrentTrial().centerX. |
centerY |
You can access the vertical center of the canvas via the jsPsych.getCurrentTrial().centerY. |
Instead, please write it as follows.” See, mouse_drawing.html. Considering window.devicePixelRatio is probably unnecessary if you use the PIXI mode.
const canvas = document.getElementById("myCanvas");
const context = canvas.getContext("2d");
const centerX = canvas.width / 2 / window.devicePixelRatio;
const centerY = canvas.height / 2 / window.devicePixelRatio;
Stimuli
| Parameter |
Description |
| stimuli |
You can access the stimuli via the jsPsych.getCurrentTrial().stimuli. This is useful if you want to change the stimulus in the on_start function. |
stim_array |
You can access the stimuli via the jsPsych.getCurrentTrial().stim_array. This is useful if you want to change the stimulus in the event handlers or the raf_func. |
From the psychophysics plugin V4, stim_array can not be used. Use jsPsych.getCurrentTrial().stimuli[n].instance instead.