What is hearing?

A sound’s journey to meaning.

This is the flagship volume. We follow a single sound — “Hey Dr. Miles!” — from the pinna of the listener’s ear, down the canal, through the middle-ear bones, into the cochlea, up the auditory nerve, through the brainstem and cortex, to the moment a thought forms. Nine chapters and a coda.

The thesis is simple and somewhat audacious: hearing is not a transparent window onto the acoustic world. It is an act of inference. The cochlea sends a signal; the brain interprets it. The signal under-determines what is heard. What you actually perceive is the brain’s best guess about what generated the signal, given everything it knows about the world.

Most of the physics of the signal — air, waves, Fourier — lives in the companion volume. This book picks up at the ear.

Chapters

1. Chapter 1What did you just hear?A puzzle to begin with
   1. 1.1A demonstration
   2. 1.2What just happened
   3. 1.3The promise
   4. 1.4A cabinet of puzzles
   5. 1.5The McGurk effect
   6. 1.6Phonemic restoration
   7. 1.7The Shepard tone
2. Chapter 2The body before the earPinna, canal, head, HRTF
   1. 2.1Two ears, two signals
   2. 2.2Head shadow and diffraction
   3. 2.3The pinna
   4. 2.4The ear canal
   5. 2.5The head-related transfer function
3. Chapter 3The middle earWhy three tiny bones
   1. 3.1The impedance problem
   2. 3.2Acoustic impedance
   3. 3.3The ossicular solution
   4. 3.4Protective reflexes
   5. 3.5What arrives at the oval window
4. Chapter 4Fourier in hydraulicsThe cochlea, slowly
   1. 4.1A geometry to learn
   2. 4.2The stiffness gradient
   3. 4.3The wave on the membrane
   4. 4.4The place map
   5. 4.5The cochlear amplifier
   6. 4.6The inner hair cells
   7. 4.7What leaves the cochlea
5. Chapter 5The auditory nerveAnalog becomes spikes
   1. 5.1From receptor potential to spike
   2. 5.2Tonotopy is preserved
   3. 5.3Phase locking
   4. 5.4Rate coding above 5 kHz
   5. 5.5Dynamic range and fiber types
   6. 5.6What leaves the auditory nerve
6. Chapter 6The brainstemWhere space is computed
   1. 6.1The cochlear nucleus
   2. 6.2The superior olive
   3. 6.3ITDs in the MSO
   4. 6.4ILDs in the LSO
   5. 6.5The inferior colliculus
   6. 6.6The barn owl
   7. 6.7What leaves the brainstem
7. Chapter 7The cortexBuilding auditory objects
   1. 7.1The thalamic gate
   2. 7.2A1 and the tonotopic map
   3. 7.3Spectro-temporal receptive fields
   4. 7.4Streaming and auditory objects
   5. 7.5Belt, parabelt, dual streams
   6. 7.6Speech and music in cortex
8. Chapter 8Meaning, memory, predictionWhere the brain explains the signal
   1. 8.1The Helmholtz move
   2. 8.2Bayes for perception
   3. 8.3Hierarchical generative models
   4. 8.4Predictive coding implementation
   5. 8.5Phonemic restoration revisited
   6. 8.6Attention as precision
   7. 8.7The free-energy principle
   8. 8.8"Hey Dr. Miles!" as meaning
9. CodaCoda — Hearing as inferenceWhere we end
   1. C.1Return to the puzzle
   2. C.2The shape of what we have done
   3. C.3What we have not done
   4. C.4A last note
10. Chapter GGlossaryTerms used in this book
11. Chapter BBibliographySources and further reading

Working notes

• Voice and depth. Scholarly, graduate-notebook texture. Math taught on-page, derivations not hidden. Grad-level where insight requires it.
• Substrate. Astro + MDX + Svelte islands. KaTeX for math. Web Audio for sound. Vanilla SVG for figures.
• Status. Chapter 4 (cochlea) is the most polished. Every chapter has at least one main interactive plus prose.
• Imagery. All anatomy figures are public-domain (NIDCD/NIH, Gray’s Anatomy 1918) or CC BY (Zetes et al. 2012 SEM and diagram). See planning/visual-resources.md in the repo for the full catalog.