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Endnotes: The Six Physical Human Senses

Endnotes: The Six Physical Human Senses

Back to Topics │Abstract Senses│ Start: Relativity & Reaction
– Nerd Cheat Sheet: The Six Physical Human Senses

Abstract Senses explores how humans see and interpret the world. These references also underpin the data used in: Nerd Cheat Sheet: The Six Physical Human Senses.

(a) Sight

  • Human retina: ~120M rods and ~6M cones (American Academy of Ophthalmology).
  • Human acuity: ~20/20; eagle acuity ~20/5 (~2–4× sharper, depending on method). Source: Nature review (Potier et al. 2016).
  • Colour vision: Humans are trichromatic (~10M colours). ~12% of women carry a fourth cone variant (possible tetrachromacy). Many birds and insects are tetrachromatic (incl. UV). Mantis shrimp have 12–16 receptor types plus polarisation sensitivity (Current Biology).
  • Popular overview: “90 Animals Ranked by Eyesight” (OCLI Vision) — useful context but not peer-reviewed.

(b) Hearing

  • Humans: ~20 Hz–20 kHz in young adults, peak sensitivity at 2–5 kHz (NCBI Bookshelf).
  • Greater wax moth: detects ultrasound up to ~300 kHz (PubMed, 2013).
  • Comparative context: Bats echolocate ~20–120 kHz; dolphins use ~40–150 kHz clicks.

(c) Motion (non-visual)

  • Humans: Vestibular thresholds ~0.006–0.01 g for linear acceleration; angular velocity thresholds ~0.4–0.7°/s at ~1–2 Hz (NASA Technical Reports; ResearchGate).
  • Flies: Halteres act as gyroscopes, detecting rotation at wingbeat frequencies ~200 Hz (PNAS).
  • Fish: Lateral line detects water displacements <1 μm (PMC).
  • Birds: High-performance fliers show exceptional vestibular precision.

(d) Smell

  • Humans: ~6–10M olfactory neurons; ~400 functional receptor genes (NCBI).
  • Dogs: >220M receptors (PMC review).
  • Elephants: largest receptor gene repertoire (~2,000+) in mammals (Genome Research, 2015).

(e) Taste

  • Humans: ~5k–10k taste buds (Cleveland Clinic).
  • Catfish: >100k, sometimes ~175k, distributed across body (PubMed review).
  • Cows/rabbits/pigs: ~15k–25k taste buds.

(f) Touch

  • Humans: Fingertip mechanoreceptor density ~241 units/cm²; SA1 (Merkel) ~100/cm². Two-point discrimination thresholds ~1–2 mm (Physiopedia; PMC).
  • Star-nosed mole: ~25k Eimer’s organs; prey captured in ~120–230 ms (PubMed).
  • Octopus: Chemotactile receptors in suckers, enabling “taste by touch” (Cell, 2015).

(p) Wiring & Cortex Allocation

  • Vision: ~30–50% of cortex devoted to visual processing.
  • Hearing: ~3–4%.
  • Somatosensory: ~8–10%.
  • Smell: <1%.
    Sources: standard neuroscience reviews (PMC, textbooks).

Back to Topics │Abstract Senses│ Start: Relativity & Reaction
– Nerd Cheat Sheet: The Six Physical Human Senses

📖 Series Roadmap

  1. Forward: A Little Background
  2. Introduction: Action, Reaction, and the Human Paradox (16.09.2025)
  3. Looking Back in Time: The Development of the Human Brain (23.09.2025)
  4. Abstract Senses: Enhancing the way we see the world outside (30.09.2025)
  5. Bias as a Concept & Climbing the Stairs: Pattern Recognition & Everyday Tasks (07.10.2025)
  6. Abstract Feelings and Abstract Senses (14.10.2025)
  7. Motivation (04.11.2025)
  8. The Social Knowledge Base (11.11.2025)
  9. Potential (18.11.2025)
  10. The Subliminal Way We Go Through Life (26.11.2025)
  11. Taking Responsibility (02.12.2025)
  12. Fishing for Complements (22.12.2025)
  13. Peter and Fermi (22.12.2025)

🔗 R&R Navigation

Back to Topics │Abstract Senses│ Start: Relativity & Reaction
– Nerd Cheat Sheet: The Six Physical Human Senses

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