Head shadow enhancement with low-frequency beamforming improves sound localization and speech perception for simulated bimodal listeners

TL;DR

This paper introduces a low-frequency beamforming method to enhance head shadow cues, significantly improving sound localization and speech perception in simulated bimodal listeners, with potential clinical applications.

Contribution

A novel head shadow enhancement technique using a fixed beamformer that improves interaural level differences and speech-in-noise performance for bimodal listeners.

Findings

Localization error reduced from 50.5° to 26.8° RMS.

Speech reception thresholds improved by up to 15.7 dB SNR.

Method is computationally simple and suitable for clinical devices.

Abstract

Many hearing-impaired listeners struggle to localize sounds due to poor availability of binaural cues. Listeners with a cochlear implant and a contralateral hearing aid -- so-called bimodal listeners -- are amongst the worst performers, as both interaural time and level differences are poorly transmitted. We present a new method to enhance head shadow in the low frequencies. Head shadow enhancement is achieved with a fixed beamformer with contralateral attenuation in each ear. The method results in interaural level differences which vary monotonically with angle. It also improves low-frequency signal-to-noise ratios in conditions with spatially separated speech and noise. We validated the method in two experiments with acoustic simulations of bimodal listening. In the localization experiment, performance improved from 50.5{\deg} to 26.8{\deg} root-mean-square error compared with standard omni-directional microphones. In the speech-in-noise experiment, speech was presented from the frontal direction. Speech reception thresholds improved by 15.7 dB SNR when the noise was presented from the cochlear implant side, improved by 7.6 dB SNR when the noise was presented from the hearing aid side, and was not affected when noise was presented from all directions. Apart from bimodal listeners, the method might also be promising for bilateral cochlear implant or hearing aid users. Its low computational complexity makes the method suitable for application in current clinical devices. Keywords: head shadow enhancement, enhancement of interaural level differences, sound localization, directional hearing, speech in noise, speech intelligibility PACS: 43.60.Fg, 43.66.Pn, 43.66.Qp, 43.66.Rq, 43.66.Ts, 43.71.-k, 43.71.Es, 43.71.Ky