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Gaze and Fixations

Gaze and Fixations are closely related. Gaze records the HMD position over time and the direction of the eyes at a set interval. Fixations use a dispersion technique to identify where the participant's eyes are steady and maintaining focus.

When using an HMD without Eye Tracking, Fixations will not be recorded and Gaze will assume the participant's focus is directly in front of the HMD.

Setup

Add the Player Tracker component to your Player Actor. This will automatically record Gaze when the Session begins.

We use the 3rd party eye tracking plugins to record Fixations and Gaze using Eye Tracking. Add any Eye Tracking SDKs to your project's Plugins folder. For example, if you are using the Vive Pro Eye, you will need to put the SRanipal SDK into your Plugins folder. The plugin dependencies should be configured automatically. For completeness, you can find the code snippets on the Troubleshooting page.

Fixation Recorder Component

When using an SDK with supported Eye Tracking, attach a Fixation Recorder component to your Player Actor. There are several parameters on the component to configure how Fixation points are recorded.

The default values are taken from several academic papers and should be suitable for most projects.A high level summary is available at Fixations

  • Max Fixation Distance - The maximum distance a Fixation will be recorded at
  • Min Fixation Ms - The time that gaze must be within the Max Fixation Angle before a Fixation begins
  • Max Fixation Angle - The angle that a number of gaze samples must fall within for a Fixation to begin
  • Max Blink Ms - The maximum amount of time that can be assigned as a single 'blink'. If eyes are closed for longer than this, assume that the user is consciously closing their eyes
  • Pre Blink Discard Ms - When a blink occurs, ignore gaze preceding the blink up to this far back in time
  • Blink End Warmup Ms - After a blink has ended, ignore gaze up to this long afterwards as the participant re-focuses
  • Saccade Fixation End Ms - Amount of consecutive eye samples before a Fixation ends as the eye fixates elsewhere. This is the most common way of fixations ending
  • Max Consecutive Discard Ms - The amount of time gaze can be discarded before a fixation is ended. Gaze can be discarded if the eye tracker returns unexpected values
  • Max Consecutive Off Dynamic Ms - Amount of time gaze can be off the transform before fixation ends. Mostly useful when Fixation is right on the edge of a Dynamic Object
  • Focus Size From Center - This curve increases the size of the Max Fixation Angle as gaze gets toward the edge of the viewport. This is used to reduce the number of incorrectly ended fixations because of hardware limits at the edge of the eye tracking field of view