Electro-Haptic Stimulation: A New Approach for Improving Cochlear-Implant Listening

Abstract

Cochlear implants (CIs) have been remarkably successful at restoring speech perception for severely to profoundly deaf individuals. Despite their success, several limitations remain, particularly in CI users' ability to understand speech in noisy environments, locate sound sources, and enjoy music. A new multimodal approach has been proposed that uses haptic stimulation to provide sound information that is poorly transmitted by the implant. This augmenting of the electrical CI signal with haptic stimulation (electro-haptic stimulation; EHS) has been shown to improve speech-in-noise performance and sound localization in CI users. There is also evidence that it could enhance music perception. We review the evidence of EHS enhancement of CI listening and discuss key areas where further research is required. These include understanding the neural basis of EHS enhancement, understanding the effectiveness of EHS across different clinical populations, and the optimization of signal-processing strategies. We also discuss the significant potential for a new generation of haptic neuroprosthetic devices to aid those who cannot access hearing-assistive technology, either because of biomedical or healthcare-access issues. While significant further research and development is required, we conclude that EHS represents a promising new approach that could, in the near future, offer a non-invasive, inexpensive means of substantially improving clinical outcomes for hearing-impaired individuals.

Keywords: cross-modal; haptic sound-localization; hearing aid; hearing impaired; neuroprosthetic; somatosensory; tactile aid; vibrotactile.

FIGURE 1

Number of publications each year from 1970 to 2020. Data taken from Google Scholar searches for articles (including patents, not including citations) with the term “tactile aid” (shown in blue) or “cochlear implant” (shown in red) in the title. The search was conducted on 07/02/2021.

FIGURE 2

Block diagram describing the haptic signal-processing strategy used by Fletcher et al. (2019).

FIGURE 3

Image of the mosaicOne_C device currently being developed at the University of Southampton as part of the Electro-Haptics Project. Text and arrows highlight that the device has four motors (extruding from the wristband), which are faded between to create the sensation of haptic stimulation at continuum of points around the wrist. Image reproduced with permission of Samuel Perry and Mark Fletcher.