# Sensory Systems and Illusions

> Vision, hearing, and the vestibular system in aviation.

- **Subject:** 040 — Human Performance Limitations
- **Section:** 040-02 — Basics of Aviation Physiology and Health Maintenance
- **Topic code:** 040-02-02
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/human-performance-limitations/basics-of-aviation-physiology-and-health-maintenance/people-and-the-environment-the-sensory-system/

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## Vision
The primary source of information for pilots ("See and Avoid").
*   **Retina**: Contains Photoreceptors.
    *   **Cones**: Central vision (Fovea), detailed, color, require bright light (Photopic).
    *   **Rods**: Peripheral vision, movement detection, black & white, sensitive in low light (Scotopic).
*   **Blind Spots**:
    *   **Anatomical**: Where the optic nerve exits (no receptors).
    *   **Night Blind Spot**: The Fovea (Cones) is blind at night. Pilots must look off-center to use Rods.
*   **Empty Field Myopia**: In featureless skies (blue sky, haze, dark night), the eye tends to focus at a resting distance of ~1-2 meters, making distant traffic detection difficult.

## Vestibular System (Balance)

![Vestibular balance system](https://upload.wikimedia.org/wikipedia/commons/7/7a/Vestibular_balance_system.jpg)

Located in the inner ear.
1.  **Semicircular Canals**: Detect angular acceleration (Rotation: Pitch, Roll, Yaw).
2.  **Otoliths (Utricle & Saccule)**: Detect linear acceleration (Gravity, Speed up/down).

## Illusions (Spatial Disorientation)
When visual cues are lost (IMS/night), the vestibular system can mislead.
*   **The Leans**: A slow roll is undetected by the canals (below threshold). A sudden correction feels like a roll in the opposite direction.
*   **Coriolis**: Moving the head during a steady turn stimulates multiple canals, causing unbearable tumbling sensation.
*   **Somatogravic Illusion**:
    *   **Take-off (Acceleration)**: Otoliths interpret acceleration as a pitch up. Pilot pushes nose down $\rightarrow$ CFIT.
    *   **Deceleration**: Interpreted as pitch down. Pilot pulls nose up $\rightarrow$ Stall.

## Hearing
*   **Noise Induced Hearing Loss (NIHL)**: Prolonged exposure to high decibels (>90 dB) damages the hair cells in the cochlea. High frequencies are lost first.

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