What can we do to take full advantage of the wireless revolution?

(top row, L to R) Arthur Boothroyd, PhD, is professor emeritus at the City University of New York, resident scholar at San Diego State University, and distinguished visiting scientist at the House Ear Institute in Los Angeles; Kelly Fitz, PhD, is a research engineer at Starkey Hearing Research Center in Berkeley, Calif; Jon Kindred, PhD, is in the CERL Sound Group at the University of Illinois, Urbana; Sergei Kochkin, PhD, is executive director of the Better Hearing Institute, Alexandria, Va; (bottom row, L to R) Harry Levitt, PhD, is professor emeritus at the City University of New York and the former director of the Rehabilitative Engineering Research Center (RERC), New York City; Brian C. Moore, PhD, is professor of auditory perception at the University of Cambridge in England; and Jerry Yanz, PhD, is the senior trainer at Starkey Laboratories, Eden Prairie, Minn.

It's obvious that hearing aid technology and wireless technology are converging quickly. The big question is what can we do to prepare the hearing care field for the wireless revolution and better serve the public's comprehensive and individual hearing needs?

Over the last 20 years, hearing aid adoption rates have remained at about one in five people who admit to hearing loss.¹ Even among adopters, many report limited utility, especially in noisy situations.² In a recent survey, only 29% of respondents were either "satisfied" or "very satisfied" with performance in noise.³

Poor performance in noise is also given as a primary reason for nonadoption. This opinion is sometimes based on personal experience and sometimes on negative reports by disappointed hearing aid users in the social network.⁴ An additional, related complaint is inability to hear distributed speech in public places such as museums, theaters, lecture halls, and places of worship.

Wireless technology offers a proven solution to these problems and may have other applications that improve the effectiveness and acceptability of hearing aids. The purpose of this paper is to review existing and potential wireless applications and to outline needs for the future.

Wireless Reception of Audio Signals

Foremost among existing applications is the wireless reception of sounds from a remote source. The wireless receiver is either an accessory to the hearing aid or an integral component. The main goal is to reduce or eliminate the negative effects of talker distance, room noise, and room reverberation. A microphone is placed within a few inches of the talker's mouth, and its output is carried by wireless link to the listener, usually—but not necessarily—using frequency modulation (FM). The magnitude of the signal-to-noise ratio (SNR) improvement is 15 dB to 20 dB, which far exceeds that provided by in-the-aid solutions such as directional microphones and digital noise management.⁵

In spite of its proven ability to address the problems of noise and distance, the remote wireless microphone has yet to find general application in the audiological management of adult hearing loss. In fact, only one in 200 consumers reports using an FM system with his or her hearing aid.³ Some of the reasons for low penetration may be inherent in the technology itself. For example, it is intrusive, it is only effective for the speech of the person with a microphone, and there is potential wireless interference. Moreover, simultaneous activation of the wireless and hearing aid microphones can reduce the SNR benefit unless the two gains are properly balanced.

Other reasons for nonacceptance may lie with the user. For example, they may lack the understanding or adaptability needed to use this technology effectively, have unreasonable expectations, or be resistant to the added complexity. Another potential barrier is cost, especially for the user who has already spent a large sum on high-end digital hearing aids, expecting them to function adequately in noisy environments.

Underlying many of the limitations just mentioned is the failure of the audiological community to recognize and embrace the wireless microphone as a solution to one of the principal problems reported by hearing aid users. Dispensing professionals are often unable or unwilling to provide the demonstration, instruction, coaching, and counseling needed to ensure effective use and realistic expectations. Part of this failure reflects the training of audiologists and hearing aid dispensers. Profit margin may also be an issue in relation to the additional patient-contact time. And, for both the makers and dispensers of hearing aids, there is an inevitable bias in the direction of trying to address all patient needs with in-the-aid technology.

There are, however, some encouraging developments in this area. Several manufacturers have produced hearing aids with built-in wireless receivers, and one manufacturer has addressed the need for multiple microphones in a group setting with the use of frequency-hopping technology. At the same time, the clinical research literature is providing evidence of improved use and acceptance following appropriate instruction, demonstration, coaching, and counseling.⁶

Other potential audio sources for a wireless link include radios, televisions, MP³ players, transponders (ie, relay devices for magnetic loops or infrared transmitters), and cell phones. For persons with unilateral hearing loss, a microphone and transmitter can be placed in a hearing aid case worn on the impaired ear (a wireless CROS fitting) to eliminate the head-shadow effect. These applications are obvious and available.

Also available is wireless transmission from a handheld or head-mounted, beam-forming microphone. By using multiple microphone elements with greater spacing than is possible within a hearing aid, these devices attain high directionality and enhanced SNR for the speech of the talker at whom they are pointed. They also have the advantage of remaining under the user's control and, therefore, are less intrusive than the remote microphone. This last benefit, however, comes with a significant loss of effectiveness. At best, the signal-to-noise benefit is considerably less than the 15 dB to 20 dB that can be attained with a close-talking microphone, and it continues to decrease as talker distance increases. An additional problem is that, by the time the user has identified the current talker in a group and reoriented the microphone, some or all of that talker's contribution is lost.

Unlike the wireless carrier-wave systems just discussed, the telecoil is well established as an option for the wire-free reception of audio signals.⁷ Developed originally to take advantage of stray magnetic signals from a telephone receiver, the technology has also been applied to the reception of other audio signals, using installed loops, and as a method of coupling the output of a wearable device to the hearing aid (using either a neck loop or a silhouette loop next to the aid).

There are, however, several inherent limitations to loop systems. The telecoil cannot be miniaturized without loss of sensitivity. The correct alignment for telephone use is often less than optimal for installed loops and neck loops. There is no resistance to interference from electrical wiring and equipment. Additionally, the amplitude of the received audio signal varies with distance of the telecoil from the magnetic source. (A few years ago, Phonic Ear developed TMX technology that used a form of pulse-width coding to eliminate many of the problems with telecoil reception from neck loops.⁸) Although technologically inferior to the wireless carrier-wave approach, the telecoil does have the advantage of low cost. This advantage is likely to shrink, however, with improvements in wireless technology and its growing application in consumer electronics.

There may be benefits to the use of digital coding as an alternative to FM in wireless audio links to hearing aids. It would be beneficial, for example, if a hearing aid could receive digital-audio transmissions directly from Bluetooth-enabled devices. Unfortunately, the necessary bandwidth and circuit complexity are, at this writing, incompatible with the miniaturization and electrical current constraints of hearing aids. One manufacturer has produced an accessory with its own power supply that can be attached to a behind-the-ear aid to provide Bluetooth connectivity to a cell phone,⁹ and at least one manufacturer has recently introduced a Bluetooth-compatible accessory that is designed to interface with an array of communication devices and provide binaural transmission between the aids.¹⁰ Whether digital capabilities can be incorporated effectively into an audio-wireless receiver within the aid on a widespread basis (eg, becoming an industry "standard" feature), using Bluetooth or an application-specific alternative has yet to be determined (Table 1).

TABLE 1. Estimate of current status of two options for digital wireless reception in hearing aids. Note the pressing need for industrywide collaboration on the development of standards for low-power digital wireless hearing aid applications. *Note also that wireless protocols are undergoing rapid development. Many current products will deviate from these estimates, and the situation could change dramatically in the near future.

In summary, there are many applications for the wireless reception of audio signals within a hearing aid. The benefits are known and considerable, and the technology is available. There are, however, several barriers to general acceptance. These barriers are associated with the technology itself, the user, the audiological community, the manufacturing community, cost, and complexity.

Wireless Reception of Data Signals

The transmission and reception of control data via a carrier-wave link is technologically less demanding than the transmission of audio signals. For this reason, there may be good reasons to incorporate data-specific wireless receivers within hearing aids. An existing application is the use of a remote control for user adjustment of volume and other hearing aid settings. Another is the reception of control data from an aid on the opposite ear to ensure binaural synchronization¹¹ in adaptive mode. Some manufacturers already incorporate both audio and data reception into FM wireless systems.

Among other possible applications is the elimination of cables for the programming of hearing aids (hopefully, using an industry-wide standard protocol). As an adjunct to built-in audio wireless receivers, a Bluetooth-like system for identifying and negotiating with available sources could also have value.

Wireless Transmission of Audio Signals

Hearing aids could, at some future date, include not only the reception of audio signals but also their transmission. There has already been some investigation into possible signal-to-noise improvement by combining and processing bilateral signals and returning them to the ears with enhanced interaural differences.^12,13 The measured benefits were on the same order as those that can be obtained monaurally with directional microphones, but further research may lead to more effective algorithms. Note also that existing processing algorithms may give clinically significant benefits in specific situations, such as listening in a car.¹⁴

Another potential application is the transmission of audio samples to some external storage device—either at random or at the user's request. The resulting samples could be used by an audiologist to reevaluate prescriptive settings or by the external device to accumulate information about user difficulties and to modify hearing aid settings in an automated "learning" mode. One could also conceive of two-way wireless communication between two (or more) users with hearing loss. These applications are speculative, and any attempts to realize them would need to be preceded by considerable proof-of-concept research.

Wireless Transmission of Data Signals

Less speculative is the incorporation of wireless data transmission into hearing aids. This application already exists in binaural systems that compare and coordinate settings in adaptive mode.¹⁵ There are, however, other possible applications including external datalogging to provide more detail and more learning options than are currently possible with internal circuitry.¹⁶

David Myers, PhD, says we should loop America with audiocoils, as they have done in many European countries. His articles, "The Coming Audiocoil Revolution" and "Heard Round the World: Hearing Aid Compatibility and Wireless Assistive Devices." are in the September 2002 and January 2005 HR Archives.

Some research questions in relation to potential but unproven applications:

1. Binaural processing. Are there ways of processing the outputs from bilateral aids so as to enhance binaural cues and provide a meaningful enhancement of SNR in both reverberant and nonreverberant surroundings, or in specified listening situations?^11-13
2. Audio and datalogging. Is there anything to be learned from actual audio samples and/or derived spectra and levels, collected either at random intervals or at user request, that could be useful for the manual or automatic modification of hearing aid settings so as to enhance performance and satisfaction?¹⁶
3. Fully integrated wireless. Are there ways of integrating reliable audio- and data-wireless receivers into the "mother board" of a digital aid with minimal increase of cost and maximum simplicity of operation?

Encouraging Developments

One of the more encouraging developments at this writing is the increasing use, acceptance, and visibility of wireless communication by the hearing public. It is now "cool" to wear a Bluetooth receiver. This in itself may encourage wider use of wireless accessories by hearing aid users. At the same time, an increasing convergence of consumer electronics and hearing aid technology could lead to economies of scale, reduced cost, and simplicity of operation. Yet another consequence of this trend could be the incorporation of the special needs of persons with hearing loss into consumer electronics. Practitioners should be prepared for this eventuality.²⁰

References

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