Formant frequencies are encoded by F0 fluctuation amplitude across auditory nerve fibres.

Evidence

In the healthy ear, the fibres that are “captured” by a single harmonic and have responses with relatively flat envelopes. In contrast, fibres tuned to frequencies between formants respond to multiple harmonics and strong rate fluctuations at F0. The amplitude of F0-related neural fluctuations provides a robust code for the formant frequencies. — Dijk, Pim van, Physiology, Psychoacoustics and…, 5473

Categorization

• DEFINE: Explains synchrony capture: how one harmonic dominates near a spectral peak, flattening that fibre’s envelope.