Localization and interaural time difference (ITD) thresholds for cochlear implant recipients with preserved acoustic hearing in the implanted ear

Abstract

The purpose of this study was to investigate horizontal plane localization and interaural time difference (ITD) thresholds for 14 adult cochlear implant recipients with hearing preservation in the implanted ear. Localization to broadband noise was assessed in an anechoic chamber with a 33-loudspeaker array extending from −90 to +90°. Three listening conditions were tested including bilateral hearing aids, bimodal (implant + contralateral hearing aid) and best aided (implant + bilateral hearing aids). ITD thresholds were assessed, under headphones, for low-frequency stimuli including a 250-Hz tone and bandpass noise (100–900 Hz). Localization, in overall rms error, was significantly poorer in the bimodal condition (mean: 60.2°) as compared to both bilateral hearing aids (mean: 46.1°) and the best-aided condition (mean: 43.4°). ITD thresholds were assessed for the same 14 adult implant recipients as well as 5 normal-hearing adults. ITD thresholds were highly variable across the implant recipients ranging from the range of normal to ITDs not present in real-world listening environments (range: 43 to over 1600 μs). ITD thresholds were significantly correlated with localization, the degree of interaural asymmetry in low-frequency hearing, and the degree of hearing preservation related benefit in the speech reception threshold (SRT). These data suggest that implant recipients with hearing preservation in the implanted ear have access to binaural cues and that the sensitivity to ITDs is significantly correlated with localization and degree of preserved hearing in the implanted ear.

Using ILD or ITD Cues for Sound Source Localization and Speech Understanding in a Complex Listening Environment by Listeners With Bilateral and With Hearing-Preservation Cochlear Implants

“…The cochlear damage that resulted in elevated low-frequency thresholds likely alters the internal representation of fine-timing information. The and Gifford, Grantham, et al (2014) reports of significantly poorer-than-normal ITD thresholds for listeners with hearing-preservation CIs are consistent with this hypothesis. In addition, the settings, for example, gain and automatic gain-control settings, employed on two independent hearing aids may add to the distortion of the internal representation of fine-timing information.…”

“…For these listeners, successful preservation of low-frequency hearing in the operated ear, in conjunction with low-frequency hearing in the contralateral ear, allows access to ITD cues but minimal access to ILD cues (Gifford, Dorman, Sheffield, Teece, & Olund, 2014;Gifford, Grantham, et al, 2014). Listeners with hearing-preservation CIs, similar to listeners with bilateral CIs, are able to locate sound sources and have poorer than normal-localization accuracy (Dunn, Perreau, Gantz, & Tyler, 2010;Loiselle, Dorman, Yost, & Gifford, 2015).…”

Hearing Preservation Outcomes With a Mid-Scala Electrode in Cochlear Implantation

“…In those patients, several studies have demonstrated benefit to patients in music appreciation, directional cues, and speech recognition in noise situations (2)(3)(4)(5)(6)(7)(8). Given these findings, and considering hearing preservation as a surrogate marker for atraumatic insertion with implantation, surgeons have been challenged to maximize the cochlea's residual hearing during implantation.…”

Estimation of Trajectory and Location for Mobile Sound Source

“…In contrast to the other studies, the locations of sound sources are taken by only two microphones. Furthermore, two common terms for sound localization process which are ITD and Interaural Level Differences (ILD) are used [15][16]. The parameters of ITD and ILD are time and amplitude difference between signals received by microphones or sensors [17].…”