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Hearing Aids for the Pediatric Population
Published in Stavros Hatzopoulos, Andrea Ciorba, Mark Krumm, Advances in Audiology and Hearing Science, 2020
Katia de Almeida, Maria Cecíli Martinelli
Specifically, all the advantages and functions of binaural hearing will be somewhat impaired, such as the sound localization, the binaural summation, and the elimination of the head shadow effect. More than 20% of children with permanent hearing loss are initially diagnosed with unilateral hearing loss. About 40% of these are at risk for deterioration of hearing in both the ear with hearing loss and the ear with normal hearing (Fitzpatrick et al., 2017).
Physiology of Hearing
Published in John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed, Paediatrics, The Ear, Skull Base, 2018
Soumit Dasgupta, Michael Maslin
The role of the pinna in localization of sound cannot be underestimated.7 It has been postulated that the unique position of the pinna on the head and its relative size to the craniofacial skeleton transform the incoming sound signal with delay paths dependent on the wavelengths of the acoustic waveform to provide localization clues for the listener to an incoming signal. The head shadow, i.e. the intervening head and the pinna on either side, is an important factor for auditory localization, with interaural time and interaural intensity differences generated by the same acoustic signal impinging on the pinna with different temporal and intensity values at each side.8
Binaural and spatial hearing
Published in Stanley A. Gelfand, Hearing, 2017
The traditional duplex theory of localization was introduced by Lord Rayleigh (John William Strutt) in 1907. It explains localization on the basis of time differences between the ears at lower frequencies and level differences between the ears at higher frequencies. Consider the arrangement in Figure 13.4a. The signal from the speaker, which is off to the right, must follow a longer path to the far (left) ear than to the near (right) ear. As Figure 13.4b shows, low frequencies have wavelengths that are longer than the path around the head, so that they “bend around” the head to the far ear (diffraction). Thus, interaural time differences (ITDs) are expected to provide localization cues for the lower frequencies, where the wavelength of the tone is larger than the distance the signal must travel from the near (right) ear to the far (left) ear. In contrast, higher frequencies have wavelengths smaller than the head, so that they are “blocked” in the path to the far (left) ear (Figure 13.4c). This head shadow causes a reduction in the intensity of the signal at the far ear, producing sound level differences between the ears. Thus, interaural level differences (ILDs) or interaural intensity differences (IIDs) are expected to provide localization cues for the higher frequencies. Our thresholds for interear differences as small as approximately 10 μs for ITDs (Klumpp and Eady, 1956) and about 1 dB for ILDs (Mills, 1960; Blauert, 1997)
CI in single-sided deafness
Published in Acta Oto-Laryngologica, 2021
Anandhan Dhanasingh, Ingeborg Hochmair
The simple presence of head in a natural sound field creates a diffraction pattern of sound waves, leading not only to ILDs but to different signal-to-noise ratio (SNR) in the two ears, whenever the signal and the noise from different directions compete with each other. The ear that is further to the source of noise will have an increase in SNR due to head attenuation of noise, and the ratio decreases at the ear that is closer to the noise source. This is known as the head-shadow effect, and it is a phenomenon of binaural hearing, helping the subject to focus on the ear that is turned towards the source of the main sound, leaving the other ear turned towards the source of noise [13]. The head shadow effect is frequency dependent. High-frequency information (>1,500Hz) is affected more than the low-frequency information because the wavelengths for high-frequency sounds are shorter. Therefore, high-frequency sounds will be attenuated much more than low-frequency information. High frequencies can be attenuated by up to 20 dB or more, and low frequencies can be attenuated by approximately 3–6dB [14]. Consequently, patients with SSD are at a disadvantage every time the critical sound comes from the impaired side, even in quiet environments, and the disadvantage increases in the presence of background noise.
Bimodal benefit for cochlear implant listeners with different grades of hearing loss in the opposite ear
Published in Acta Oto-Laryngologica, 2018
Ulrich Hoppe, Thomas Hocke, Frank Digeser
Obviously, the better-ear advantage is important in everyday life. Furthermore, in an acoustic environment with spatially separated sources of signal and noise, the advantages of bilateral hearing in making use of the head shadow have a major impact on all recipients. When speech and noise are emitted from the same sound source and the reference is the better ear, it is possible to make assumptions about binaural processing in bimodal mode without having to consider the superposition by head shadow or better ear advantage. Additionally, the positive effects of binaural squelch do not obscure any negative effect that might have occurred as a result of binaural interference. Hence, the here presented data for bimodal benefit can be seen as a conservative estimation.
Bilateral cochlear implantation
Published in Acta Oto-Laryngologica, 2021
Anandhan Dhanasingh, Ingeborg Hochmair
The ear transmits sound waves to the brain, and having an ear on each side of the head helps with localising the direction of the sound. The term binaural hearing refers to normal hearing with two ears. The hearing has two primary functions: communication (speech recognition) and warning (acoustic source localisation). The critical task for the central auditory pathways is to break down the auditory messages sent by the two ears into auditory objects. The segregation and localisation of auditory objects constitute an essential means of separating target signals from noise and competing sources. With asymmetric or single-sided deafness, or with a cochlear implant (CI) on one side, the monaural exploitation of sound messages significantly lessens the performance compared to what it should be in a binaural situation [1]. Binaural hearing in normal-hearing individuals offers speech intelligibility, sound source localisation, understanding the speech in a noisy environment, and hearing with enough loudness. Technically, the benefits or effects of binaural hearing can be brought under the terms head-shadow, squelch, summation and localisation (Figure 1). In brief, the head-shadow effect results from the physical placement of the head which acts as an acoustic barrier and attenuates sound (speech or noise) on one ear if that sound (speech or noise) comes from the other ear. Squelch effect corresponds to the brain’s ability to suppress background noise and attend to a specific auditory signal that comes binaurally. Summation effect, also known as loudness summation, refers to the identical loudness perception due to balanced action potentials coming from both ears to the auditory brainstem. Localisation is the ability to perceive directions of where different sounds are coming from, and it helps with the orientation [2].