Spatial Hearing by Bilateral Cochlear Implant Users With Temporal Fine-Structure Processing

Abstract

Several studies have demonstrated the advantages of the bilateral vs. unilateral cochlear implantation in listeners with bilateral severe to profound hearing loss. However, it remains unclear to what extent bilaterally implanted listeners have access to binaural cues, e.g., accurate processing of interaural timing differences (ITDs) for low-frequency sounds (<1.5 kHz) and interaural level differences (ILDs) for high frequencies (>3 kHz). We tested 25 adult listeners, bilaterally implanted with MED-EL cochlear implant (CI) devices, with and without fine-structure (FS) temporal processing as encoding strategy in the low-frequency channels. In order to assess whether the ability to process binaural cues was affected by fine-structure processing, we performed psychophysical ILD and ITD sensitivity measurements and free-field sound localization experiments. We compared the results of the bilaterally implanted listeners with different numbers of FS channels. All CI listeners demonstrated good sensitivity to ILDs, but relatively poor to ITD cues. Although there was a large variability in performance, some bilateral CI users showed remarkably good localization skills. The FS coding strategy for bilateral CI hearing did not improve fine-structure ITD processing for spatial hearing on a group level. However, some CI listeners were able to exploit weakly informative temporal cues to improve their low-frequency spatial perception.

Intensive Training of Spatial Hearing Promotes Auditory Abilities of Bilateral Cochlear Implant Adults: A Pilot Study

“…Some authors suggest that the fine-structure temporal processing implemented in some processors (e.g., FS4 in MED-EL) improves ITD cues and helps patients with some auditory skills (e.g., music perception, Roy et al 2015). In accordance with a recent study showing that patients with a fine-structure ITD processing did not perform better on a spatial localization task (Ausili et al 2020), participants in our sample fitted with this technology were not those who showed the most improvement in sound localization performance. Bilateral CI users also experience difficulties extracting ILD cues because the magnitude of ILDs is decreased by the compression applied by the CI processor.…”

Effects of place of stimulation on the interaural time difference sensitivity in bilateral electrical intracochlear stimulations: Neurophysiological study in a rat model

“…Ausili et al. (2020) tested 25 bilateral CI recipients implanted with the MED‐EL 31 mm FLEXsoft or Standard array, which had the maximum insertion depth (into the end of the middle turn of the cochlea) of commercially available electrodes, with fine‐structure temporal processing as encoding strategy in the low‐frequency channels (up to 1 kHz). Using this encoding strategy in the low‐frequency channels, the temporal representation of the low‐frequency fine structure can be potentially improved.…”

“…Consequently, simultaneous ILD changes during free-field sound localization would cause ITD tuning of monotonic-type neurons to shift outside the behaviorally relevant range. Therefore, although both peak-and monotonic-type IC neurons are sensitive to ITDs of electrical stimulation, selective apical stimulation of the low-frequency pathway could lead to better sensitivity to ITDs compared with basal stimulation Ausili et al (2020). tested 25 bilateral CI recipients implanted with the MED-EL 31 mm FLEXsoft or Standard array, which had the maximum insertion depth (into the end of the middle turn of the cochlea) of commercially available electrodes, with fine-structure temporal processing as encoding strategy in the low-frequency channels (up to 1 kHz).…”

Stimulation Crosstalk Between Cochlear And Vestibular Spaces During Cochlear Electrical Stimulation

“…Although there is a positive impact of the CI on balance described in other publications, these results may be related to the effect of spatial information from the sound information as well as localization of the sound source. 19 Other findings showed a positive impact while using a CI (attached to an inertial motion), by using different sounds for coding the tilt and roll of the head. 6 Other authors observed improved balance 1 year after cochlear implantation and attributed this to central compensation.…”