Sensitivity to haptic sound-localisation cues

Abstract

Hearing aid and cochlear implant (CI) users often struggle to locate and segregate sounds. The dominant sound-localisation cues are time and intensity differences across the ears. A recent study showed that CI users locate sounds substantially better when these cues are provided through haptic stimulation on each wrist. However, the sensitivity of the wrists to these cues and the robustness of this sensitivity to aging is unknown. The current study showed that time difference sensitivity is much poorer across the wrists than across the ears and declines with age. In contrast, high sensitivity to across-wrist intensity differences was found that was robust to aging. This high sensitivity was observed across a range of stimulation intensities for both amplitude modulated and unmodulated sinusoids and matched across-ear intensity difference sensitivity for normal-hearing individuals. Furthermore, the usable dynamic range for haptic stimulation on the wrists was found to be around four times larger than for CIs. These findings suggest that high-precision haptic sound-localisation can be achieved, which could aid many hearing-impaired listeners. Furthermore, the finding that high-fidelity across-wrist intensity information can be transferred could be exploited in human–machine interfaces to enhance virtual reality and improve remote control of military, medical, or research robots.

Can Haptic Stimulation Enhance Music Perception in Hearing-Impaired Listeners?

“…The dynamic range of the tactile system at the arm, wrist, and hand is similar to that available to HA users and is around four times larger than that available through electrical CI stimulation ( Verrillo et al, 1969 ; Moore et al, 1985 ; Zeng and Galvin, 1999 ; Zeng et al, 2002 ; Fletcher et al, 2021a , b ). CI users are able to discriminate approximately 20 different intensity steps across their dynamic range ( Kreft et al, 2004 ; Galvin and Fu, 2009 ).…”

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

“…The dynamic range for electrical CI stimulation is around 10–20 dB ( Zeng and Galvin, 1999 ; Zeng et al, 2002 ). The dynamic range of the tactile system at the fingertip or wrist, however, is around four times larger (∼60 dB; Verrillo et al, 1969 ; Fletcher et al, 2021a , b ). Across the dynamic range, approximately 40 intensity steps can be discriminated with haptic stimulation ( Gescheider et al, 1996b ), whereas CI users can discriminate around 20 intensity steps ( Kreft et al, 2004 ; Galvin and Fu, 2009 ).…”

“…These include the capture of audio from an onboard microphone that is highly susceptible to wind noise and disruption from movement of clothing across the device. Previous EHS studies have advocated streaming of audio from behind-the-ear hearing-assistive devices, which already include technologies to address many of the issues faced by the Buzz (e.g., wind noise; Fletcher, 2020;Fletcher and Zgheib, 2020;Fletcher et al, 2020aFletcher et al, , 2021a. This approach would also allow access to spatial-hearing cues and would increase the correspondence between audio and haptic stimulation, facilitating maximal multisensory integration.…”

“…Using this approach, large improvements were shown in both sound-localization accuracy ( Fletcher and Zgheib, 2020 ; Fletcher et al, 2020a ) and speech reception for spatially separated speech and noise ( Fletcher et al, 2020b ). Two recent studies have investigated sensitivity to across-wrist tactile time and intensity differences ( Fletcher et al, 2021a , b ). Encouragingly, participants could detect tactile intensity differences across the wrists of just 0.8 dB, which is similar to (or perhaps even better than) sensitivity to sound intensity differences across the ears ( Grantham, 1984 ).…”

“…The ability to discriminate haptic stimulation at different locations on the skin has also been found to worsen with age ( Leveque et al, 2000 ). However, intensity discrimination both at a single stimulation site ( Gescheider et al, 1996a ) and across sites ( Fletcher et al, 2021a ) has been found to be robust to aging. The evidence of decline in some aspects of haptic performance might suggest that EHS benefit will be reduced in older populations.…”