Improving cochlear implant listening using vibrotactile stimulation

Abstract

Cochlear implants (CI) have revolutionised the management of severe to profound hearing loss. The development of CIs has significantly improved the quality of life of individuals with severe and profound hearing loss. Although CIs provide many benefits, there are still limitations, especially when it comes to challenging listening tasks such as speech perception in noisy surroundings, sound localisation and pitch perception. A potential method to enhance performance in these challenging tasks is supplementing poorly delivered cues through haptic stimulation in conjunction with cochlear implant electrical stimulation, which is known as electro-haptic stimulation (EHS). However, despite the potential benefits of EHS, further research is required to understand and maximise the benefits of this type of bimodal stimulation. Thus, the project’s aim is to expand knowledge of EHS by optimising its speech-in-noise performance by evaluating different haptic cues and body stimulation sites, as well as to gather the perspectives and recommendations of CI users and professionals regarding the technology. To achieve this aim, three studies were conducted. In the first study, three different speech cues – fundamental frequency (F0) and amplitude envelope (Env) and speech presence (SP, which involves providing haptic stimulation on the wrists when speech is present) were compared – to identify the most effective cue for enhancing speech-in-noise performance when delivered through haptic stimulation on the wrists. In this study, twelve CI-simulated participants were trained for 90 minutes in each of the following conditions: speech presence, amplitude envelope, F0, and without haptic cues. The speech reception threshold (SRT) comparison after training did not show statistically significant differences in the benefits between cues. In contrast to the findings of previous studies, the SRTs of various vibration conditions that successfully enhanced speech in previous research were not statistically different from the audio-only control condition. The second study aimed to determine the optimal body site for haptic stimulation. The main aim was divided into two sub-aims: (a) to assess CI-simulated subjects’ perceived benefit and comfort (using a questionnaire) and (b) to evaluate SRT in noise performance when applying amplitude envelope haptic cues to the fingertips, wrists, and forearms. The 24 subjects’ SRTs were measured with and without haptic stimulation at each site after the completion of four training sessions for all body sites. There was a clear advantage in speech-in-noise performance for haptic conditions over the audio-only condition, with an average improvement of about 2 dB SNR (p < 0.001). However, there was no statistical difference in speech-in-noise benefits among the three body sites. Similarly, the questionnaire did not reveal a significant difference between the three sites in terms of comfort and perceived benefits. In conclusion, effective haptic devices could be deployed at any of the evaluated body sites. In the third study, the perspectives and preferences of CI users and professionals regarding the development of haptic devices were gathered. This study used a multi-method qualitative design that involved the administration of questionnaires and focus group discussions with ten CI users and seventeen CI professionals. Their perspectives in the focus group and the final questionnaire were thematically analysed. Six main themes emerged from the focus groups and questionnaires: (a) possible benefits of haptic devices, (b)potential candidates, (c) features and aspects to consider, (d) inhibiting factors influencing users, (e) factors likely to influence uptake, and (f)feedback on the proposed prototype. The participants in the study identified several challenges with CI listening, including hearing in noisy environments, difficulty understanding speech from a distance, difficulties with sound localization, and difficulty enjoying music. They expressed the belief that a haptic device may help with some of these difficulties while also providing additional benefits such as increased awareness of sound and improved safety. Several potential users of EHS technology were identified including those who are deaf and blind. A haptic device should be designed with consideration of the needs of users. Generally based on the discussions, potential users are looking for haptic devices that are aesthetically pleasing, comfortable to wear, easy to use and have the ability to communicate wirelessly with other devices. Additionally, the focus group discussions revealed a priority for incorporating haptic stimulation into existing wearable devices for both aesthetic and functional reasons. This study provides insights into the desired preferences and requirements for haptic devices, which developers should consider when designing these devices. Overall, these studies investigated various aspects of electro-haptic stimulation, using a holistic approach by integrating experimental studies with potential user perspectives. The findings suggest that EHS holds promise as a supplementary tool for improving speech-in-noise performance. Importantly, future studies should emphasise enhancing and optimising the design and training regimes for haptic cues to effectively observe their benefits. Moreover, the insights from CI users and professionals may provide potential guidance for the design and development of haptic devices. By synthesising this information together, this work can contribute to advancing the potential of haptic stimulation to enhance the lives of individuals with severe hearing loss. 

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