Date: March 11th

Time: 9:30am-11:00am

Location: Lefrak 1171

Title: The Relationship Between Auditory Asymmetries, Interaural Loudness Mismatch, and Free‑Field Localization in Bilateral Cochlear‑Implant and Normal‑Hearing Individuals

Speaker: Obada J. AlQasem

Abstract: Binaural cues [interaural time differences (ITDs) and interaural level differences (ILDs)] are crucial for perceiving changes in spatial locations. In intracranial lateralization tasks, diotic stimuli (i.e., 0-ITD/ILD) are commonly assumed to be perceived as single, fused, and centered auditory images by normal-hearing (NH) individuals. Bilateral cochlear-implant (BICI) users often perceive bilaterally loudness-balanced stimuli presented simultaneously as off-centered owing to interaural loudness mismatch (ILM). The reasons for ILM in BICI users remain unknown. This dissertation aims to measure ILM in BICI users through an intracranial ILD lateralization task. Additionally, it investigates whether interaural neural health asymmetry, estimated from the electrically evoked compound action potential (ECAP) amplitude growth function (AGF) slope (i.e., a measure of neural response growth with increasing stimulation levels), could explain the ILM. In addition, it aims to conduct extensive control measurements in NH individuals to assess whether they exhibit ILM and whether this can be explained by peripheral interaural asymmetries, including behaviorally measured hearing thresholds and loudness perception asymmetries. Moreover, it aims to investigate the possible functional effects of ILM (i.e., increased horizontal localization bias) in both populations. We hypothesized that BICI users and NH individuals would demonstrate ILM. Additionally, we hypothesized that ILM would be positively correlated with interaural ECAP AGF asymmetry in BICI users and with interaural thresholds and/or loudness-perception asymmetries in NH individuals. Moreover, we hypothesized that ILM would positively correlate with the magnitude of localization bias in the free field. The results of these experiments provide valuable data needed to understand the effects of binaural asymmetries on binaural perception and spatial hearing in both NH individuals and BICI users.

Date: March 26th

Time: 12:30pm-1:30pm

Location: Morrill 1101

Title: Transmission and Processing of Binaural Cues with Bilateral Cochlear Implants

Abstract: Bilateral inputs provide major benefits across sensory systems, which is why 10-20% of the approximately one million cochlear-implant (CI) users worldwide have bilateral CIs (BI-CIs). Although BI-CI listeners experience many quality-of-life improvements after surgery, their spatial-hearing abilities remain poorer than those of normal-hearing (NH) listeners. This difference likely reflects several interacting limitations, but the exact mechanisms and potential solutions remain unclear. Making CIs more effective in noise could alleviate a significant health, social, and quality of life burden for CI listeners and healthcare providers. The overarching goal of this dissertation is to broaden the field’s understanding of binaural processing under electrical stimulation and identify potential strategies for improving spatial hearing in BI-CI listeners. Study 1 quantified the binaural cues created by BI-CIs programmed with different stimulation strategies for various types of acoustic stimuli and was designed to identify potential processing-related distortions to binaural cues. Results for Study 1 showed that spectral-peak picking stimulation strategies commonly used in BI-CIs introduce processing-related distortions to cues necessary for spatial hearing, whereas constantly stimulating strategies better preserve these cues. Study 2 used observer weighting analyses to determine how BI-CI listeners process and integrate binaural information to perform spatial-hearing tasks. Results revealed that, when conveyed using bilaterally synchronized direct stimulation equipment, interaural time differences (ITDs) encoded via pulse timing in electrical stimulation improve performance on lateralization and localization tasks (beyond that achievable with interaural level differences alone). Lastly, Study 3 proposed and evaluated methods to overcome the known binaural rate limitation in BI-CI listeners using multi-electrode stimulation, emphasizing clinical implementation. Study 3 found that for multi-electrode stimulation, shortening the inter-electrode pulse interval (the time between pulses) results in ITD lateralization responses equivalent to those of single-electrode stimulation. Together, these studies identify multiple avenues for potentially improving spatial hearing in BI-CI listeners. They expand the field’s understanding of binaural processing with electrical stimulation and can inform the development of future signal processing, sound coding, and device-hardware changes that may improve the encoding of spatial information with BI-CIs.

Speaker: Jennifer Markfeld

 

Date: April 27th

Time: 9:00-10:30 CRD / 10:45-11:45 WCC

Location: Lefrak 2166

Speaker: Nan Bernstein Ratner

 

Date: May 1st

Time: 12:30-1:30pm

Location: TBA

Date: May 11th

Time: 12:00-12:50pm

Location: Lefrak 2166