JPM, Vol. 12, Pages 1971: Towards a Consensus on an ICF-Based Classification System for Horizontal Sound-Source Localization

Sound localization is an important aspect of hearing, and its preservation or restoration is a major goal of hearing implant technologies. Sound localization measurement is commonly performed both in the assessment of the rehabilitation of hearing implant users, as well as in psychophysical research to improve hearing implant performance. Across institutions, there exist major variations in localization assessment. These include variations in the testing procedure as well as in the statistical and reporting metrics used. A standardized testing procedure has been reported elsewhere [29]; however, the latter source of variation remains an issue within the audiological community. Here, the HEARRING group proposes a standardized classification system based on the ICF framework. The ICF framework is endorsed by the WHO and is used worldwide as the standard for measuring and describing health and disability (World Health Organization, 2001). Therefore, it provides a common language to define different perspectives of health (biological, psychological, and social) on an individual level, focusing on consequences of health conditions rather than causes. Using this common language, one is able to investigate the effect of an intervention (such as cochlear implantation) on different perspectives of hearing, such as audibility, speech perception, and sound localization. Danermark et al. developed the ICF core set for hearing loss in 2010, but no patient-centered CI outcome assessment protocol based on the ICF currently exists [34,35,36,37,38,39]. Therefore, we aimed to define a CI outcome assessment protocol, including all relevant ICF categories to describe the impact of cochlear implantation on different aspects of health. One of them is sound localization with code b2302. This paper introduces a standardized classification system which can categorize individuals, according to their localization performance, into one of five ICF categories based on the severity of impairment, if present. We were able to demonstrate the improvement in comparability across institutes, localization testing setups, and listeners by applying the HEARRING_LOC_ICF scale on retrospective data. For example, when we pooled data from SSD CI recipients from different institutes, the same trends across institutes were observed, with the majority of the SSD patients experiencing complete impairment of sound localization in the unaided condition and moderate impairment in the aided condition. In the majority of the SSD CI group from UWA, on the other hand, only mild impairment was observed in the aided condition. This could be explained by the intensive training program the SSD CI recipients are offered, resulting in better sound localization accuracy [40]. Earlier research in SSD patients also reported significant improvement in localization accuracy after cochlear implantation. The study of Arndt et al., for example, found an improvement from 33.9° to 15.0° in 11 SSD CI recipients [41]. Another study from Grossman et al. found an improvement from 63.2° (SD 22°) to 27.6° (SD 6.5°) in a similar SSD CI population. Since the localization testing setup was different in both studies, reported data cannot be compared or pooled. The setup from Arndt et al., for example, includes 7 speakers and uses 10 presentations per speaker (70 presentations) whereas the setup from Grossman et al. includes 9 speakers and 5 presentations per speaker (45 presentations). Both variables are known to affect the accuracy of sound localization. The standardized classification system will provide individuals such as those who are typically not familiar with the interpretation of degrees of error with a clearer understanding of the general magnitude of the localization impairment, as well as improvements derived from hearing implant use.

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