World-Space Covert Cueing — Standalone Demo

A minimal, self-contained Unity project demonstrating the world-space cueing technique for guiding visual attention in 3D environments. This project accompanies our research paper and allows readers to reproduce and experiment with the technique locally.

Overview

Covert cueing subtly modulates (flickering effect) objects in a viewer's peripheral vision to draw their attention, while suppressing the effect when the viewer looks directly at the object. The cue operates below conscious awareness — the viewer's gaze is guided without them realizing a visual manipulation is occurring.

This technique was originally developed by Monthir Ali, Po-Jui Huang, and Rogelio E. Cardona-Rivera for use with VR eye-tracking headsets (HTC Vive with Wave SDK). This standalone demo replaces hardware eye tracking with simulated gaze (camera forward direction via mouse look), making it accessible to anyone with Unity installed.

How the Technique Works

The covert cueing system has three interconnected components:

1. The Shader (Covert_S.shader — QEDLab/Covert)

A custom CG/HLSL shader that adds a radial brightness boost to an object's surface:

• Computes the world-space distance from each rendered pixel to a center point (_CenterPosition)
• Normalizes this distance into a 0–1 falloff based on _Radius (1.0 at center, 0.0 at edge)
• Adds brightness: color += 0.095 * falloff * _Modulation
• The 0.095 constant produces an approximately 9.5% maximum brightness increase — subtle enough to avoid conscious detection
• A _Color tint property allows setting the object's base color (multiplied with the texture)

2. The Cueing Controller (CovertObject.cs)

Attached to each object that should act as a covert cue:

• Sends shader parameters each frame: center position, radius, and a time-varying modulation value
• Modulation: Driven by an AnimationCurve evaluated at Time.time % 0.2f, creating a repeating 0.2-second pulse cycle
• Gaze detection: Computes the angle between the player's gaze direction and the direction toward the object
• Running average: Smooths the angle measurement over a sliding window of 5 samples to prevent flickering
• Threshold: If the smoothed angle ≤ 15 degrees (foveal vision), the radius is set to 0 (cue suppressed). If > 15 degrees (peripheral vision), the radius is restored (cue active)

3. The Gaze Provider (SimulatedEyeSight.cs)

A singleton that provides the current gaze direction:

• In this demo: uses Camera.main.transform.forward (mouse look direction = simulated gaze)
• In the original VR implementation: used EyeManager.GetCombinedEyeDirectionNormalized() from HTC Vive Wave SDK
• Interface: SimulatedEyeSight.Instance.Trans.forward — the gaze direction vector

4. Gaze Radius Overlay (GazeRadiusOverlay.cs)

An on-screen visualization that makes the invisible gaze threshold visible:

• Draws a circular outline on screen representing the 15° foveal threshold
• A crosshair at the center marks the current simulated gaze point
• Objects inside the circle are in foveal vision — their cue is suppressed
• Objects outside the circle are in peripheral vision — their cue is active
• Text labels indicate the zones and controls for quick understanding
• Attached to the Main Camera; can be toggled on/off via the Show Labels checkbox in the Inspector

Key Parameters

Parameter	Value	Description
Brightness boost	0.095 (9.5%)	Maximum RGB increase per channel at the center of the effect
Gaze threshold	15 degrees	Angle below which the cue is suppressed (foveal vision)
Running average window	5 samples	Number of frames used to smooth gaze angle measurements
Modulation cycle	0.2 seconds	Period of the temporal pulse/flicker pattern
Radius	2.0–3.0 units	Spatial extent of the brightness falloff from the object center

How to Run

1. Open this project in Unity 2022.3 LTS or later
2. Open the scene: Assets/Scenes/SampleScene.unity
3. Press Play
4. Use WASD to move, mouse to look around
5. Press Escape to unlock cursor, click to re-lock

How to Observe the Effect

1. Walk near any of the cue target objects (colored cylinders, cubes, and sphere scattered around the gray environment)
2. Notice the white circle on screen — this is the 15° foveal threshold boundary
3. Look away from an object so it falls outside the circle — it will subtly pulse brighter in your peripheral vision
4. Look directly at the object (bring it inside the circle) — the pulsing stops
5. The effect is intentionally subtle; look for slight brightness changes at the edges of your vision

Re-integrating VR Eye Tracking

To use real eye-tracking hardware instead of simulated gaze:

1. Replace SimulatedEyeSight.cs with a class that reads from your eye-tracking SDK
2. Ensure your replacement exposes Instance.Trans.forward as the gaze direction vector
3. The rest of the system (CovertObject.cs and Covert_S.shader) requires no changes
4. You may want to disable or remove GazeRadiusOverlay since the gaze circle is a demo aid

Using Custom 3D Models

1. Apply a material using the QEDLab/Covert shader to your model
2. Set the _Color property to tint the material (darker colors make the brightness boost more visible)
3. Add the CovertObject component to the GameObject
4. Set the Radius to cover the object's visual extent
5. Configure the Carve AnimationCurve for the desired pulse pattern

Adjusting the Technique

• Brightness intensity: Modify the 0.095f constant in Covert_S.shader (line with col.rgb +=)
• Gaze threshold: Change the 15f value in CovertObject.cs (runningEyeSightAngleAvg <= 15f) and update gazeThresholdDegrees in GazeRadiusOverlay to match
• Smoothing: Adjust the capacity field in CovertObject.cs (higher = more smoothing, slower response)
• Pulse speed: Change the 0.2f modulo value in CovertObject.cs (Time.time % 0.2f)

Requirements

• Unity 2022.3 LTS or later
• Built-in Render Pipeline (not URP or HDRP)
• No external packages required

Citation

Ali, Monthir, Po-Jui Huang, and Rogelio E. Cardona-Rivera. "World-Space Cueing: A Geometrically-Compact Modulation Technique for Subtle Gaze Direction in Head-Mounted Virtual Reality Displays." In 2025 IEEE International Conference on Artificial Intelligence and eXtended and Virtual Reality (AIxVR), pp. 10-18. IEEE, 2025.

License

MIT License