Volley theory

In the case of auditory neurons, this means firing an action potential at a certain phase of a stimulus sound being delivered.

[3] Volley theory suggests that groups of auditory neurons use phase-locking to represent subharmonic frequencies of one harmonic sound.

[4] In the presence of -40 to -100 decibel single tones lasting 15 or 30 seconds, recordings from the auditory nerve fibers showed firing fluctuations in synchrony with the stimulus.

Pitch is hypothesized to be determined by receiving phase-locked input from neuronal axons and combining that information into harmonics.

In his model, Terhardt claims that the spectral-analysis output of complex sounds, specifically low frequency ones, is a learned entity which eventually allows easy identification of the virtual pitch.

Helmholtz claimed that the cochlea contained individual fibers for analyzing each pitch and delivering that information to the brain.

Georg von Békésy developed a novel method of dissecting the inner ear and using stroboscopic illumination to observe the basilar membrane move, adding evidence to support the theory.

Correspondingly, William Rutherford provided evidence that this hypothesis was true, allowing greater accuracy of the cochlea.

In 1886, Rutherford also proposed that the brain interpreted the vibrations of the hair cells and that the cochlea did no frequency or pitch analysis of the sound.

Through more research, it was determined that because phase synchrony is only accurate up to about 1000 Hz, volley theory cannot account for all frequencies at which we hear.

For sounds with frequencies between 1000 and 5000 Hz, both theories come into play so the brain can utilize the basilar membrane location and the rate of the impulse.

[10] Due to the invasiveness of most hearing related experiments, it is difficult to use human models in the study of the auditory system.

Many revolutionary concepts regarding hearing and encoding sound in the brain were founded in the late nineteenth and early twentieth centuries.

Békésy isolated the cochlea from human and animal cadavers and labeled the basilar membrane with silver flakes.

In 1983, it was shown that subjects with low frequency sensorineural hearing loss demonstrated abnormal psychophysical tuning curves.

This conclusion is due to the finding that when deprived of basilar membrane place information, these patients still demonstrated normal pitch perception.