Users of hearing-assistive devices often struggle to locate and segregate sounds, which can make listening in schools, cafes, and busy workplaces extremely challenging. A recent study in unilaterally implanted CI users showed that sound-localisation was improved when the audio received by behindthe-ear devices was converted to haptic stimulation on each wrist. We built on this work, using a new signal-processing approach to improve localisation accuracy and increase generalisability to a wide range of stimuli. We aimed to: (1) improve haptic sound-localisation accuracy using a varied stimulus set and (2) assess whether accuracy improved with prolonged training. Thirty-two adults with normal touch perception were randomly assigned to an experimental or control group. The experimental group completed a 5-h training regime and the control group were not trained. Without training, haptic sound-localisation was substantially better than in previous work on haptic sound-localisation. It was also markedly better than sound-localisation by either unilaterally or bilaterally implanted CI users. After training, accuracy improved, becoming better than for sound-localisation by bilateral hearing-aid users. These findings suggest that a wrist-worn haptic device could be effective for improving spatial hearing for a range of hearing-impaired listeners. Users of hearing-assistive devices, such as hearing aids and cochlear implants, often struggle to locate and segregate sounds 1-4. As well as impairing threat detection, this makes listening in complex acoustic environmentssuch as, schools, cafes, and busy workplaces-highly challenging. Cochlear implants (CIs) enable severely-toprofoundly deaf individuals to perceive sound by electrically stimulating the auditory nerve. Recently, it has been shown that this electrical stimulation can be augmented by providing missing sound information through haptic stimulation ("electro-haptic stimulation") 5-11. Historically, a small number of studies in young normal-hearing listeners have explored the possibility of using haptic stimulation on the fingertips to locate sounds 12-15 , but research in this area is extremely sparse. In a recent study by Fletcher et al., it was shown that sound-localisation can be substantially improved in CI users by augmenting the CI signal with haptic stimulation on the wrists 10. This haptic stimulation was derived from audio signals that would be received by behind-the-ear hearing aids or CIs. Localisation accuracy increased after 30 min of training, with the same speech-sample used for both testing and training. In this study, we developed a new signal-processing strategy for haptic sound-localisation, which incorporated linked multi-band compression and wrist sensitivity correction. This was intended to improve haptic sound-localisation accuracy and increase the generalisability of the approach to a wide range of stimuli. The first aim of this study was to assess localisation accuracy with this new signal-processing strategy. To ensure that results were gen...

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.

Cochlear implants (CIs) recover hearing in severely to profoundly hearing-impaired people by electrically stimulating the cochlea. While they are extremely effective, spatial hearing is typically severely limited. Recent studies have shown that haptic stimulation can supplement the electrical CI signal (electro-haptic stimulation) and substantially improve sound localization. In haptic sound-localization studies, the signal is extracted from the audio received by behind-the-ear devices and delivered to each wrist. Localization is achieved using tactile intensity differences (TIDs) across the wrists, which match sound intensity differences across the ears (a key sound localization cue). The current study established sensitivity to across-limb TIDs at three candidate locations for a wearable haptic device, namely: the lower tricep and the palmar and dorsal wrist. At all locations, TID sensitivity was similar to the sensitivity to across-ear intensity differences for normal-hearing listeners. This suggests that greater haptic sound-localization accuracy than previously shown can be achieved. The dynamic range was also measured and far exceeded that available through electrical CI stimulation for all of the locations, suggesting that haptic stimulation could provide additional sound-intensity information. These results indicate that an effective haptic aid could be deployed for any of the candidate locations, and could offer a low-cost, non-invasive means of improving outcomes for hearing-impaired listeners.