Human Performance and Limitations
Senses and processing
Vision. The retina has cones (colour and detail, need good light, concentrated in the fovea) and rods (sensitive in low light, poor acuity, no colour, best in peripheral vision). Dark adaptation takes around 30 minutes and is destroyed by a flash of white light; red light preserves night vision. Common defects: myopia (short sight), hypermetropia (long sight), presbyopia (age-related loss of accommodation, a reading problem), colour vision deficiency (red/green most common) and empty-field myopia at night.
Hearing spans roughly 20 Hz to 20 kHz, degrades with age (presbycusis) and irreversibly with noise exposure; the first loss is usually around 4 kHz.
Information processing runs: sensing, perception, decision, response. Perception is not passive: expectation, habit, colour and contrast produce illusions, so a technician can see a familiar part where a different one is fitted.
Memory: sensory store (very brief), short-term/working memory (about 7 plus or minus 2 items, seconds to a minute without rehearsal - hence chunking and written aids), long-term memory (effectively unlimited, needs cues).
Attention is limited, and vigilance falls off over long inspection periods. Claustrophobia and physical access matter in fuel tanks, wing bays and avionics compartments: restricted entry, poor lighting, awkward posture and panic risk all raise error rates and make the attendant-outside rule essential.
Trap
Exams love mixing rod and cone functions, and confusing short-term memory capacity with duration.
Worked example: a technician must read a torque value then fetch a tool. He cannot reliably hold more than a few items, so the value belongs on the task card, not in his head.