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[AUDITORY] Presenting of the Temporal Auditory Imaging Theory
Dear all,
As is widely known, the function of the human eye can be explained relatively straightforwardly using basic optical principles, where the eye can be likened to a camera with a single lens, whose image appears on the retina, where it is transduced and neurally encoded. Despite a long tradition of drawing analogies between vision and hearing, the ear has resisted a comparably simple description. I would like to present a rigorous analogy between the optics of the eye and the signal processing of the ear all the way to the midbrain. According to this novel theory, the distance from the visual object is analogized to cochlear dispersion, the crystalline lens to a cochlear time lens, and the distance between the lens and the retina to the neural dispersion between the cochlea and the inferior colliculus. The "currency" of the auditory signal turns out to be the degree of coherence of the acoustic source.
While undoubtedly many of you may find these ideas speculative, I believe that they can be well established using available evidence from literature with relatively few missing elements. Should it be accepted, this theory could have high explanatory power and open new avenues of understanding the hearing function and its internal logic.
With more than 1500 references, the theory synthesizes ideas from numerous people on the Auditory List, past research in acoustics and hearing, and findings from related disciplines:
I invite you to explore this text and these ideas and decide for yourselves.
Any feedback, questions, suggestions for refinements or corrections would be most welcome.
Thank you,
Adam Weisser, PhD.
Treatise on Hearing: The Temporal Auditory Imaging Theory Inspired by Optics and Communication
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 familiar transformations from the visual system of diffraction between the object and the eye, spatial lensing by the crystalline lens, and second diffraction between the lens and the retina. However, 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 the defocus 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, predominantly.
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. It provides an anchor for a dual coherent and noncoherent auditory detection further downstream in the auditory brain. Phase locking enables conservation of coherence between the mechanical and neural domains.
Combining the logic of both imaging and phase locking, it is speculated that the auditory system should be able to dynamically adjust the proportion of coherent and noncoherent processing that comprises the final image or detected product. This can be the basis for auditory accommodation, in analogy to the accommodation of the eye. Such a function may be achieved primarily through the olivocochlear efferent bundle, although additional accommodative brainstem circuits are considered as well.
The hypothetical effect of dispersion and synchronization anomalies in hearing impairments is considered. While much evidence is still lacking to make it less speculative, it is concluded that impairments as a result of accommodation dysfunction and excessive higher-order aberrations may have a role in known hearing-impairment effects.