Before the popularization of cochlear implants (CI), one of the means to assist people with hearing loss was through tactile aids, or haptic devices—tools that relayed information through the sense of touch. By the late 1990s, the development of cochlear implantation rendered haptic aids obsolete. Recently, however, technological advances have produced devices for electro-haptic stimulation (EHS), reviving scientific interest in the use of haptics to support people with hearing loss.
A review titled “Electro-Haptic Stimulation: A New Approach for Improving Cochlear-Implant Listening” published in Frontiers in Neuroscience offers an optimistic glimpse into this field. It concluded 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 individuals with hearing loss.
The study's main inquiry was on the use of electro-haptic stimulation to bridge the limitations still experienced by cochlear implants users, specifically speech perception in noisy environments, locating sound sources, and hearing music. Reviewing existing literature, the authors found that there is “compelling evidence that haptic stimulation can augment the CI signal, leading to enhanced speech-in-noise performance, sound localization, and music perception.”
In addition, the review found that modern haptic devices may also assist individuals who could benefit from CI but cannot access or use one.
“[T]he time is right for a new generation of haptic devices to aid the large number of people who are unable to access or benefit from a CI, whether for biomedical reasons or because of inadequate health care provision,” the paper stated.
Coauthor Mark D. Fletcher, PhD, senior research fellow at the University of Southampton Auditory Implant Service, shared with The Hearing Journal a brief background of their haptics research.
“The original inspiration for me was a public science book I read back in 2007 while I was an undergraduate, The Brain That Changes Itself by Norman Doidge. He describes wonderful studies where researchers sent the information that is usually provided through one sense through another sense; for example, allowing people to ‘see’ through touch. It took me a while to get from there to the Institute of Sound and Vibration Research, where I could try out providing sound information through touch.
“It turns out people have tried this before (mostly in the 1980s) as an alternative to a cochlear implant, but that as the cochlear implant got better, these ‘tactile aids’ were dispensed with.”
Haptic devices have come a long way since the 1980s. Today's prototypes and publicly marketed devices are wearable on the wrist or hand, with audio processors that recognize sounds and automated motors that apply corresponding vibrations to the wearer's skin.
The authors wrote, “Particularly important are advances in micro-motor, micro-processor, wireless communication, and battery technology, as well as in manufacturing and prototyping techniques such as 3D printing. These technologies will allow modern haptic devices to avoid many of the pitfalls of early tactile aids, such as bothersome wires, large power, and computing units, highly limited signal-processing capacity, and short battery lives.”
Apart from their practical and aesthetic improvements, “modern haptic devices can deliver haptic signals with higher precision and deploy cutting-edge signal-processing techniques to substantially improve auditory feature extraction, particularly in the presence of background noise.”
However, the authors highlighted in their review that there are still areas for further investigation. They noted that the benefits of EHS have not been explored across various user groups. They also hoped to see more studies on the neuroanatomical basis of EHS, and on the training of EHS users for maximized benefit.
For Fletcher, a priority area for future research should be real-world trials of these new wearable devices.
“A lot of the technology is out there already, but we need to make sure we have something that captures the sound in the right way to make sure we have the best possible signal to convert to vibrations, that we've got the best algorithms to extract the right information from the sound, and that the device delivers vibrations very accurately so we're not losing any of that important information when we transfer it to the skin,” he said.
“We're now at a point where the lab results look very exciting and give us real confidence that this is something well worth offering to patients so that they can try it out in their everyday lives,” Fletcher added. “My main aim in writing the review was to try to convince other researchers and device manufacturers of this! There's a massive amount more we can potentially do with clever algorithms and a more sophisticated device. I think it's extremely exciting!”