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 within the cone of confusion. Without the pinna, the cues provided by timing differences alone are not sufficient to accurately identify sounds in space (Moore, 2007, p. 184-185). Therefore, sound localization relies heavily on individualized anatomy and binaural integration. Changes in the ability to localize sound will be suspected when the pinna is altered (Hofman, et al, 1998).
Sound localization performance can be investigated in conjunction with a broad range of topics including but not limited to: speech perception, hearing aid algorithm performance, and physical properties of the auditory system. As a result, there is a plethora of information available that aids in understanding localization as a whole. In preparation for this research study, two specific papers that relate directly to pinna augmentation and the impact it has on localization were reviewed. Researchers have studied the effects of pinna and outer ear augmentation on localization performance. In addition, they have examined the resulting frequency composition once a stimulus is filtered through the pinna (Hofman, et al, 1998; Raykar, et al, 2005). Hofman, Van Riswick, and Van Opstal (1998) conducted a study aimed at understanding changes in localization...