Skip to content

jspsych-webgazer-calibrate

This plugin can be used to measure the accuracy and precision of gaze predictions made by the WebGazer extension. For a narrative description of eye tracking with jsPsych, see the eye tracking overview.

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
validation_points array [[10,10], [10,50], [10,90], [50,10], [50,50], [50,90], [90,10], [90,50], [90,90]] Array of points in [x,y] coordinates. The default grid is 9 points. Meaning of coordinates controlled by validation_point_coordinates parameter.
validation_point_coordinates string 'percent' Can specify percent to have validation point coordinates specified in percentage of screen width and height, or center-offset-pixels to specify each point as the distance in pixels from the center of the screen.
roi_radius numeric 200 Tolerance around the validation point in pixels when calculating the percent of gaze measurements within the acceptable range.
repetitions_per_point numeric 1 The number of times to repeat the sequence of calibration points.
randomize_validation_order bool false Whether to randomize the order of the validation points.
time_to_saccade numeric 1000 The delay before validating after showing a point. Gives the participant time to fixate on the new target before assuming that the participant is looking at the target.
validation_duration numeric 2000 If calibration_mode is set to view, then this is the length of time to show a point while calibrating. Note that if click calibration is used then the point will remain on the screen until clicked.
point_size numeric 20 Diameter of the validation points in pixels.
show_validation_data bool false If true then a visualization of the validation data will be shown on the screen after the validation is complete. This will show each measured gaze location color coded by whether it is within the roi_radius of the target point. This is mainly intended for testing and debugging.

Data Generated

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

Name Type Value
raw_gaze array Raw gaze data for the trial. The array will contain a nested array for each validation point. Within each nested array will be a list of {x,y,dx,dy} values specifying the absolute x and y pixels, as well as the distance from the target for that gaze point.
percent_in_roi array The percentage of samples within the roi_radius for each validation point.
average_offset array The average x and y distance from each validation point, plus the median distance r of the points from this average offset.
samples_per_sec numeric The average number of samples per second. Calculated by finding samples per second for each point and then averaging these estimates together.
validation_points array The list of validation points, in the order that they appeared.

Example

4 point validation using center offset mode

var validation = {
  type: 'webgazer-validate',
  validation_points: [[-200,-200], [-200,200], [200,-200], [200,200]],
  validation_point_coordinates: 'center-offset-pixels',
  show_validation_data: true
}