Intracochlear Measurements of Interaural Time and Level Differences Conveyed by Bilateral Bone Conduction Systems

Abstract

Hypothesis Intracochlear pressures (PIC) and stapes velocity (Vstap) elicited by bilaterally-placed bone anchored hearing devices (BAHD) will be systematically modulated by imposed interaural time (ITD) and level differences (ILD), demonstrating the potential for users of bilateral BAHD to access these binaural cues. Background BAHD are traditionally implanted unilaterally under the assumption that transcranial cross-talk limits interaural differences. Recent studies have demonstrated improvements in binaural and spatial performance with bilateral BAHD; however, objective measures of binaural cues from bilateral BAHDs are lacking. Methods Bone-conduction transducers were coupled to both mastoids of cadaveric specimens via implanted titanium abutments. PIC and Vstap were measured using intracochlear pressure probes and laser Doppler vibrometry, respectively, during stimulation with pure tone stimuli of varied frequency (250–4000 Hz) in ipsilateral, contralateral and bilateral ITD (−1 to 1 ms) and ILD (−20 to 20 dB) conditions. Results Bilateral stimulation produced constructive and destructive interference patterns that varied dramatically with ITD and stimulus frequency. Variation of ITD led to large variation of PIC and Vstap, with opposing effects in ipsilateral and contralateral ears expected to lead to “ITD to ILD conversion”. Variation of ILD produced more straightforward (monotonic) variations of PIC and Vstap, with ipsilateral-favoring ILD producing higher PIC and Vstap than contralateral-favoring. Conclusion Variation of ITDs and ILDs conveyed by BAHDs systematically modulated cochlear inputs. While transcranial cross-talk leads to complex interactions that depend on cue type and stimulus frequency, binaural disparities potentiate binaural benefit, providing a basis for improved sound localization and speech-in-noise perception.

Lateral Semicircular Canal Pressures During Cochlear Implant Electrode Insertion: a Possible Mechanism for Postoperative Vestibular Loss

“…Responses are overlain onto the 95% confidence interval for stapes velocities 30 , and the mean and the range of responses observed for intracochlear pressures reported previously by Nakajima et al 26 . Responses collected were consistent with previous reports 12,18,20–24 .…”

Speech Understanding and Sound Localization with a New Nonimplantable Wearing Option for Baha

“…As bone conduction has a much lower sound attenuation across the head than air conduction [ 21 , 22 ], it is not self-evident that using 2 bone conduction devices can result in a significant audiological benefit when compared to just one device. However, it is known that sound localization is possible with 2 BAHS sound processors mounted on implants, although the localization error is considerably higher than in normal hearing subjects [ 23 ].…”

Intracochlear Sound Pressure Measurements in Normal Human Temporal Bones During Bone Conduction Stimulation

“…When pressures are referenced to V prom , the referenced pressure frequency responses have multiple narrow-band fluctuations due to the three-dimensional complex motion of the bone, which is not captured in our one-directional velocity measurements (Stenfelt and Goode 2005b). Furthermore, our isolated temporal bone preparation in putty may not attenuate these sharp vibrations relative to frequency as compared to a temporal bone in the natural environment of a whole head (Banakis Hartl et al 2016;Farrell et al 2017). The overall trend of the frequency response of P SV /V prom and P Diff /V prom increases 20 dB/decade below 1 kHz, while the response is flatter between 1 and 4 kHz (Fig.…”