Treatise on Hearing: The Temporal Auditory Imaging Theory Inspired by Optics and Communication

TL;DR

This paper introduces a novel auditory imaging theory inspired by optics, modeling the ear as a temporal imaging system that processes sound coherence and enhances understanding of auditory perception and impairments.

Contribution

It presents a new theory of mammalian hearing based on optical and communication principles, detailing the ear's temporal imaging transformations and neural processing mechanisms.

Findings

Auditory system acts as a temporal imaging system with three key transformations.

Differential focusing enhances or degrades images of acoustical objects based on coherence.

The organ of Corti functions as a multichannel phase-locked loop for phase locking and coherence preservation.

Abstract

A new theory of mammalian hearing is presented, which accounts for the auditory image in the midbrain (inferior colliculus) of objects in the acoustical environment of the listener. It is shown that the ear is a temporal imaging system that comprises three transformations of the envelope functions: cochlear group-delay dispersion, cochlear time lensing, and neural group-delay dispersion. These elements are analogous to the optical transformations in vision of diffraction between the object and the eye, spatial lensing by the lens, and second diffraction between the lens and the retina. Unlike the eye, it is established that the human auditory system is naturally defocused, so that coherent stimuli do not react to the defocus, whereas completely incoherent stimuli are impacted by it and may be blurred by design. It is argued that the auditory system can use this differential focusing to enhance or degrade the images of real-world acoustical objects that are partially coherent. The theory is founded on coherence and temporal imaging theories that were adopted from optics. In addition to the imaging transformations, the corresponding inverse-domain modulation transfer functions are derived and interpreted with consideration to the nonuniform neural sampling operation of the auditory nerve. These ideas are used to rigorously initiate the concepts of sharpness and blur in auditory imaging, auditory aberrations, and auditory depth of field. In parallel, ideas from communication theory are used to show that the organ of Corti functions as a multichannel phase-locked loop (PLL) that constitutes the point of entry for auditory phase locking and hence conserves the signal coherence. It provides an anchor for a dual coherent and noncoherent auditory detection in the auditory brain that culminates in auditory accommodation. Implications on hearing impairments are discussed as well.