1.3 The promise

We will spend the next eight movements taking this thesis seriously. We are going to follow a single sound — the phrase “Hey Dr. Miles!” — from its origin as molecular vibration in air, through every stage of the auditory pathway, all the way to the moment a brain assembles it into a coherent meaning.

The journey has nine movements.

1. The puzzle — this one. We have started.
2. Sound in air. The signal as it exists before anyone hears it. Air pressure waves; the wave equation; Fourier; rooms and reverberation.
3. The body before the ear. How the head, pinna, and ear canal filter the sound before any neuron fires. Interaural time and level differences. The head-related transfer function.
4. The middle ear. Three tiny bones whose job is to overcome a thirty-decibel impedance mismatch. Impedance, leverage, area ratios.
5. The cochlea. The structural climax of the essay’s first half. The traveling wave; the Greenwood place map; the cochlear amplifier; the inner hair cells; what leaves through the auditory nerve.
6. The auditory nerve. Analog becomes digital. Spike trains; phase locking; rate coding; tonotopy preserved.
7. The brainstem. Where space is computed. Interaural time differences extracted to ten microseconds. The medial superior olive. The barn owl.
8. The cortex. Where auditory objects are built. Spectro-temporal receptive fields. Streaming. Speech and music as cortical specializations.
9. Meaning, memory, prediction. Where the brain explains the sound. Bayesian inference for perception. Predictive coding as a working framework. Why two listeners hear different things from the same waveform.

Then a coda: hearing as inference.

It is a lot. It is also where, by the end, the bistable demonstration we just made will be fully explicable — and the strangeness of it will not have dissipated but deepened.