The Human Auditory System

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Introduction

The human auditory system is incredibly accurate in identifying signal content, location, and meaning through discrete neurological processes. The accuracy of these processes begins at the external, anatomical portions of the auditory pathway: the pinna and ear canal. The pinna serves to collect sound from the environment and generate direction-dependent cues through spectral transformations (Hofman, et al, 1998; Raykar, et al, 2005). Sounds that are funneled into the ear canal contain a range of frequencies that are amplified and attenuated. This interaction of complex sound waves, based on the unique shape of an individual’s pinna, results in a transfer function used for localization in the vertical plane (Hofman, et al, 1998, p. 417). There is evidence that the spectral notches and peaks formed when sound interacts with the pinna are key component to localization of sound in the vertical plane (Raykar, et al, 2005, p. 364). The spectral changes caused by reflections of sound waves on the unique curves of the pinna are referred to as “spectral patterning”. This occurs primarily in frequencies above 6 kHz, as the wavelength of the sound is short enough for it to interact with the pinna. This indicates that sound localization is influenced most by high-frequencies (Moore, 2007, p. 186).

Each individual ear is unique and provides frequency information not offered by any other facet of the auditory pathway. The distinctive curvature and overall shape of the pinna aids in shaping complex signals to determine spatial information by integrating the frequency transforms for both ears. Therefore, it is important to be capable of receiving sound binaurally to accurately locate the signal in space and to reduce ambiguity wit...

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References

Hofman, P. M., Van Riswick, J. G., & Van Opstal, A. J. (1998). Relearning sound localization with new ears. Nature neuroscience, 1(5), 417-421.

Hone, R. (2010). Pinna augmentation and hearing gain. Otolaryngology--Head and Neck Surgery, 143(2), P243.

Kuk, F., Korhonen, P., Lau, C., Keenan, D., & Norgaard, M. (2013). Evaluation of a pinna compensation algorithm for sound localization and speech perception in noise. American Journal of Audiology, 22(1), 84-93.

Moore, Brian C.J. (2007). Cochlear Hearing Loss: Physiological, Psychological and Technical Issues. England: John Wiley & Sons, Ltd.

Raykar, V. C., Duraiswami, R., & Yegnanarayana, B. (2005). Extracting the frequencies of the pinna spectral notches in measured head related impulse responses. The Journal of the Acoustical Society of America, 118(1), 364-374.

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