ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Sound localization is the perceptual ability to locate an acoustic event in space, using only auditory information. For normal listeners, sound localization is a BINAURAL task. This is because the sounds arriving at the two ears do so at different times and with different spectra, depending on the eccentricity of the sound source with respect to the head's midline plane; it is the neural computation of these disparities in the timing and spectra of the signals at the two ears that results in the spatial percept. Interaural disparities in the timing of sounds arise because of differences in the path length to the two ears from the sound source. Interaural disparities in the spectra of the sound arise from the shadowing effect of the head (and PINNAE) for sound frequencies with wavelengths shorter than the head diameter (or pinna height). The absolute magnitude of interaural disparities depends on both the eccentricity of the source, and the frequency of the sound. Disparity magnitudes are close to zero for sources near the midline, increase with increasing source eccentricity, and plateau in the lateral hemi-fields.
Conductive mechanism
Stanley A. Gelfand in Hearing, 2017
Head-related transfer functions depend on the direction of the sound source. The fundamental nature of this azimuth effect is illustrated for two representative directions in Figure 3.2. Here, we are concerned with the sound reaching the right eardrum when it is presented from a loudspeaker at an azimuth of 45° to the right compared to being presented from a speaker at 45° to the left. The right ear is the near ear when the sound comes from the right (same side of the head), and it is the far ear when the sound comes from the left (the opposite side of the head). Note that the sound level increases going from the far ear, and that there are differences in the details of the shapes of the two curves. Physical factors of this type provide the basis for sound localization in space (see Chapter 13).
Perception of Sounds at the Auditory Cortex
John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed in Paediatrics, The Ear, Skull Base, 2018
The AC plays an important role in spatial hearing, which has been shown to underlie two major auditory functions: the ability to identify the location or the source of a sound, and auditory scene analysis or the ability to separate sounds based on their locations.31–33 Research findings in both other animals34 and humans35 have demonstrated that the accurate localization of a sound source is affected if the AC is compromised. In humans, sound localization in the horizontal plan is largely dependent on the neural processing of interaural time differences (ITDs) and interaural intensity level differences (ILDs). Research findings have demonstrated that the perceived location of low-frequency sounds is largely mediated by processing of ITDs, while perception of high-frequency sounds is more heavily weighted on the processing of ILDs.36,37 The time and intensity differences in these binaural cues are represented by excitatory and inhibitory responses in the cells of the AC.38 Within the AC, there are two main types of cells, including excitation–excitation (EE) cells and excitation–inhibition (EI) cells. EE cell responses are excitatory to stimulation at each ear, whereas EI cells usually present an excitatory response at the contralateral ear and an inhibitory response at the ipsilateral ear.38 The identification of the elevation of a sound source is based primarily on monaural spectral cues, although some weak binaural cues may be available due to small head asymmetries that often exist in individual listeners.33
Sound localization, speech and tone recognition for stimuli presented from the rear in bilateral cochlear implant users
Published in International Journal of Audiology, 2021
Yu Zheng, Ning Cong, Na Gao, Fanglu Chi, Yibo Huang, Xianhao Jia, Xinda Xu, Yang-Wenyi Liu, Ying Chen
Children with severe-to-profound hearing loss and/or adults with postlingual deafness, who can obtain scores of up to 55% for open-set phonemes in quiet in the ear to be implanted, are considered candidates for cochlear implantation (Leigh, Dettman, and Dowell 2016a; Leigh et al. 2016b). Previously, individuals were provided with only one cochlear implant (CI) even if they were experiencing severe-to-profound bilateral hearing loss. In order to achieve the goal of bilateral hearing restoration, ear, nose, and throat specialists in Wurzburg, Germany, implanted the bilateral cochlear implants (BCIs) in adults and children in 1996 and 1998, respectively (Lee, Gomez-Marin, and Lee 1996). Subsequently, the auditory performance of individuals with BCIs has been reported in many studies, in particular in terms of the benefit of binaural, as compared to monaural input (Muller, Schon, and Helms 2002; Litovsky et al. 2004). Additionally, sound localisation is one of the repeatedly studied aspects of auditory performances, since the ability to localise sounds correctly is a crucial feature of the auditory system, which is valuable in the presence of noise and reverberation. In such situations, sound localisation can help a listener identify and orient themselves rapidly towards the person speaking in a group conversation. This is particularly important for CI users, because other cues for speaker identity, such as voice pitch, are diminished by CIs (Litovsky et al. 2006).
Electrophysiological and behavioural study of localisation in presence of noise
Published in International Journal of Audiology, 2019
Varghese Peter, Luke Fratturo, Mridula Sharma
Different mechanisms have been identified regarding how the neural structures code the ITD and ILD cues for sound localisation (Andéol et al. 2011; Salminen, Tiitinen, and May 2012). In modern models of sound localisation, these functions are attributed primarily to the brainstem, as it receives inputs from both the ears (Harper and McAlpine 2004). However, auditory cortex is required for the accurate perception of sound source as the inactivation of cortical fields have shown to impair localisation (Malhotra and Lomber 2007). Indeed neural sensitivity to ITD and ILD cues is observed throughout the auditory system, typically in the form of higher firing rate to contralateral compared to ipsilateral sound sources (McAlpine, Jiang, and Palmer 2001). In the auditory cortex, this pattern is hold true for the ILD cues (Lui et al. 2015), but the evidence is mixed for ITD cues (Belliveau, Lyamzin, and Lesica 2014).
Sound localisation ability using cartilage conduction hearing aids in bilateral aural atresia
Published in International Journal of Audiology, 2020
Tadashi Nishimura, Hiroshi Hosoi, Osamu Saito, Ryota Shimokura, Toshiaki Yamanaka, Tadashi Kitahara
Sound localisation is an important ability for proper audition. It not only plays a role in optimal communication, but also contributes to maintaining safety in daily life. Cues from various auditory factors, predominantly interaural time and level differences (ITD and ILD), allow for sound localisation (Hebrank and Wright 1974; Middlebrooks and Green 1991). ITD is the difference in arrival time of a sound between two ears. ILD is the difference in loudness and frequency distribution between two ears. They provide a cue to the direction or angle of the sound source. Sound localisation does not always refer to differentiation between left and right, but the correct identification of the sound source as originating from the front, back, top, and bottom. ITD and ILD are not enough to identify the sound source because no ITD and ILD exist for sounds originating along the circumference of circular conical slices. Direction-specific reflections of sounds by the head, torso, and pinnae contribute to the identification of the sound source (Zahorik et al. 2006). Furthermore, the head movements also provide a cue to sound localisation (Brimijoin and Akeroyd 2012).
Related Knowledge Centers
- Auditory System
- Auricle
- Cochlea
- Hair Cell
- Middle Ear
- Organ of Corti
- Oval Window
- Synapse
- Eardrum
- Sound
- Organ of Corti