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

Abstract

Purpose: To assess the role of interaural time differences and interaural level differences in (a) sound-source localization, and (b) speech understanding in a cocktail party listening environment for listeners with bilateral cochlear implants (CIs) and for listeners with hearingpreservation CIs. Methods: Eleven bilateral listeners with MED-EL (Durham, NC) CIs and 8 listeners with hearing-preservation CIs with symmetrical low frequency, acoustic hearing using the MED-EL or Cochlear device were evaluated using 2 tests designed to task binaural hearing, localization, and a simulated cocktail party. Access to interaural cues for localization was constrained by the use of low-pass, highpass, and wideband noise stimuli.Results: Sound-source localization accuracy for listeners with bilateral CIs in response to the high-pass noise stimulus and sound-source localization accuracy for the listeners with hearing-preservation CIs in response to the low-pass noise stimulus did not differ significantly. Speech understanding in a cocktail party listening environment improved for all listeners when interaural cues, either interaural time difference or interaural level difference, were available. Conclusions:The findings of the current study indicate that similar degrees of benefit to sound-source localization and speech understanding in complex listening environments are possible with 2 very different rehabilitation strategies: the provision of bilateral CIs and the preservation of hearing.T he information embodied in interaural time differences (ITDs) and interaural level differences (ILDs) (a) allows listeners with normal hearing (NH) to locate sound sources on the horizontal plane, and (b) has a significant role in generating high levels of speech recognition in complex listening environments, for example, at a cocktail

Speech Understanding in Complex Listening Environments by Listeners Fit With Cochlear Implants

“…When hearing is preserved, the recipients commonly have low-frequency acoustic hearing in both the ear contralateral to the CI and in the ear with the CI. In a recent experiment Loiselle et al (2016) tested a group of unilateral CI recipients with excellent hearing preservation in the operated ear (i.e., the mean threshold at 250 Hz was 30 dB HL and thresholds were within 15 dB of the thresholds in the ear contralateral to the CI). The test environment was the cocktail party described earlier (i.e., a female talker in front and continuous male talkers at ±90°).…”

Contralateral Routing of Signal Yields Significant Speech in Noise Benefit for Unilateral Cochlear Implant Recipients

“…ftentimes, unilateral cochlear implant (CI) recipients gain significant benefits to speech understanding after receiving a second CI. This improvement is due to several possible mechanisms, which are mostly inherent to binaural hearing and include summation effects of co-located signals and maskers (Litovsky et al, 2004;Buss et al, 2008; Kokkinakis and Pak, 2014) and spatial hearing benefits most likely arising from interaural-level difference cues (Grantham et al, 2008;Dorman et al, 2016;Loiselle et al, 2016). Binaural squelch, or binaural unmasking of speech, results from a central comparison of primarily interaural time differences, resulting in improved speech understanding in noise with the addition of a second ear with a poorer signal-to-noise ratio (SNR).…”

Sound source localization is a multisystem process

“…These filter conditions were chosen in order to implicate ITD processing for the LF noise, ILD processing for the HF noise, and both ITD and ILD processing for the BB noise. Figure 3 displays data (mean, range, and standard deviation) from several published experiments [13][14][15][16][17][18][19][20] conducted by the authors regarding sound source localization accuracy measured as root-mean-square (rms) error in degrees (azimuth plane). Panel 3A are data for bilateral CI patients presented with the three filtered noises.…”