Vision & hearing

040 Human PerformanceChapter 4

Pilots acquire 70–75% of information through vision and ~13% through hearing. Understanding limitations prevents illusion-related accidents.

Schematic

Fovea = cones (day/colour/acuity). Periphery = rods (night). Scan slowly — saccades switch vision off for ~0.3 s.

The eye

Key fact

Cornea bends light most. Lens (ciliary muscle) accommodates — fatter for near objects, flatter for distant. Iris controls pupil size.

Key fact

Fovea — highest acuity, cones only, no night vision. Best vision within 2–3° of fovea; acuity drops rapidly peripherally. Visual acuity ≈ 1 minute of arc under ideal conditions.

Key fact

Rods — peripheral, monochrome, scotopic (night) vision. Cones — colour (RGB classes), photopic (day). Night adaptation: rods ~40 min, cones ~7 min after bright light. Visual purple (rhodopsin) bleached by bright light.

Key fact

Empty field myopia — with nothing to focus on, eye relaxes to 1.5–2 m. During lookout, pick a reference ≥6 m away. Saccades — jerky eye movements; vision suppressed ~0.3 s during movement — hold each lookout segment ~1 second.

Visual defects

Defect	Description	Correction
Myopia	Short-sighted — image in front of retina	Concave lens
Hypermetropia	Long-sighted — image behind retina	Convex lens
Presbyopia	Age-related lens hardening — ↓ accommodation; common >50	Reading glasses
Astigmatism	Unequal cornea/lens curvature	Cylindrical lens
Glaucoma	↑ intra-ocular pressure — pain, blindness	Puff test
Cataract	Clouding of lens	—

Key fact

Hypoxia, age, and distance from fovea reduce visual acuity. Hypoglycaemia and vitamin A deficiency impair night vision (visual purple).

Visual illusions (runway & environment)

Illusion	Cause	Pilot tendency
Narrow runway	—	Appears high → steep approach → short landing
Wide runway	—	Appears low → high approach → long landing
Upslope	—	Appears high → steep → short
Downslope	—	Appears low → shallow → long
Fog/mist	—	Objects appear farther → steep approach
Black hole	Night, no cultural lighting	Feels too high → fly below glideslope → short
Autokinesis	Staring at static light	Light appears to move
Rain on windshield	—	Runway appears closer/magnified

Exam trap

Black hole approach — pilot thinks they are too high and flies below glideslope, risking short landing. Counter: PAPI/ILS, strict instruments.

Key fact

Shallow fog creates pitch-up illusion — tendency to pitch down. Top-down illusion: smaller objects seen as farther. Bottom-up: flying over tall trees then short trees affects height perception.

Key fact

Constant bearing — another aircraft on collision course appears at constant bearing with no relative movement.

Hearing

Key fact

Hearing range 20 Hz – 20 kHz. Pain threshold ~140 dB. NIHL (noise-induced loss) depends on intensity and duration above ~90 dB. Presbyacusis — gradual high-frequency loss with age.

Key fact

Conductive hearing loss — blockage outer/middle ear; does not include auditory nerve damage. Sound transferred by ossicles to cochlea, which converts vibration to nerve impulses.

Key fact

Speak at ~125 Hz, hear best around 500 Hz. 80% of communication is metacommunication (tone, body language) — lost on radio; clear phraseology critical.