Research | September 2016 Hearing Review

Opening the door wider for the brain to receive the auditory signals it needs

Wireless connectivity in hearing aids is a powerful tool that offers significant potential communication improvement for hearing aid users. Such improvement can only be achieved when the end user is skilled in the use of wireless technology, and the hearing care professional has opened the doorway to the brain to the greatest extent possible. This is achieved through real-ear verified hearing aid programming, sufficient hearing aid use instruction, and description of the benefits and limitations of hearing aids and wireless technology.

Hearing aids, properly fit by hearing care professionals, must provide as much information to the brain as possible for every patient with hearing loss. In this context, a hearing loss might be considered a narrowing of the door to the brain. It then behooves the clinician to seek means by which this door can be opened to the greatest extent possible.

It is the thesis of this paper that wireless connectivity in hearing aids provides a major “door opener” for the person with hearing loss. As it relates to hearing aids, wireless connectivity refers to streaming acoustic signals from external microphones, telephones, sound systems, and media devices without the use of hard-wired cables.

The literature describing use of wireless connectivity in hearing aids usually follows three major areas of discussion:

1) Studies delineating the problems associated with the communication experiences of hearing aid users;

2) Studies showing that wireless connectivity in hearing aids addresses many of the problems that result in hearing aid user dissatisfaction, and

3) Studies on communication limitations not amenable to solutions by use of wireless connectivity in hearing aids.

The evidence that supports these three areas is as follows:

1) Problems Associated with the Communication Experiences of Hearing Aid Users

MarkeTrak IX shows that only 48% of 765 hearing aid owners in 2015 reported that hearing aids routinely improve their quality of life.1 In 2012, Kochkin2 noted that survey respondents reported hearing aids reduced their communication difficulty on the telephone, in meetings, at church, and in other noisy places by approximately 50%.

These two surveys, which collectively include over 3,000 hearing aid users, show that satisfaction with hearing aid performance on the telephone, in church, in classrooms, in meetings, and in other noisy places is unacceptably low. Clearly there is need for technology that improves these performance estimates.?It is our contention this technology is wireless connectivity in hearing aids.

Figure 1Acoustic factors negatively impacting aided speech understanding. At least four major acoustic factors have been identified that contribute to the communication problems of people with hearing loss:

  • Unfavorable signal-to-noise ratio,3-34
  • Reverberation,3-7,9,14,21,22,30-46
  • Disproportionate degradation of high-frequency information,47 and
  • Inverse Square Law effects.3,5,13,47,48

Figure 2

 

Figures 1-3 illustrate how these acoustic issues affect the speech understanding of a person with hearing loss in a classroom or meeting environment. These figures illustrate that sound pressure decreases markedly over distance, while background noise tends to be more constant.

Figure 3Further, as the auditory information of interest interacts with objects in the environment, unfavorable sound reflections increase reverberation and decrease signal-to-noise ratio (SNR) while disproportionately degrading critical high-frequency speech sounds.

2) Wireless Connectivity in Hearing Aids Addresses Many of the Problems Associated with Hearing Aid User Dissatisfaction

Benefits of a remote microphone. Wireless connectivity in hearing aids mitigates many of these aforementioned communication issues by use of a remote microphone. When a remote microphone is worn by the speaker, the background noise levels typically remain well below the signal of interest, the multiple sources of reverberation are reduced, the disproportionate dispersion of high-frequency energy is minimized, and the integrity of high-frequency speech sounds is maintained to a greater extent.49-59

Figure 4Figure 4 shows the increased speech sound audibility provided by a remote microphone. In this figure, the real-ear aided response (REAR) measures are shown under two different test conditions. In the first condition, the external microphone was shut off, and the real-ear data was obtained with the hearing aid microphone 5 feet from the loudspeaker of an Audioscan Axiom real-ear system using the carrot passage stimulus presented at 70 dB SPL. In the second condition, the external microphone was activated and placed 6 inches in front of the Axiom loudspeaker, and the carrot passage signal was used again as the stimulus at 70 dB SPL.

The results show that an approximate gain of 20 dB was achieved at most frequencies when the remote microphone was placed 6 inches in front of the Axiom’s loudspeaker. Obviously, such increased gain creates a dramatically better SNR and an improved aided Speech Intelligibility Index (SII). Additionally, the effects of reverberation are minimized as the microphone is placed closer to the signal of interest where the effects of reverberation are less significant. Finally, the Inverse Square Law is largely overcome as is disproportionate degradation of high-frequency speech sounds traveling over distance.

As noted in the earlier analogy, the remote microphone “widens the doorway to the brain.”

Addressing telephone problems with wireless connectivity. As noted previously, satisfaction with telephone use is also relatively poor among hearing aid users. The reasons for this dissatisfaction stem from the difficulty associated with aligning the telephone earphone with the microphone of the hearing aid, from telecoil and phone compatibility issues, and from feedback concerns.

Numerous hearing aid manufacturers provide an intermediary device that receives a Bluetooth signal from an appropriately equipped telephone and transduces that signal into the hearing aid. It is of interest to assess how listeners with “golden ears” would rate these various telephone intermediary devices for sound quality, when the person with normal hearing listens from a landline phone to the intermediary device connected to a Bluetooth-enabled landline or cell phone.

To test the sound quality of various manufacturers’ intermediary devices, 5 professional sound recording engineers were asked to give a letter grade to 5 different telephone interface devices while listening on a land-line phone in another room. These engineers were instructed not to judge the audio fidelity based on their studio monitors, but rather to base their ratings on the sound quality they typically receive from a landline telephone.

The speech signal was Az Bio Sentences presented at 65 dB SPL at a +5 dB SNR as measured at the microphone inlets of the telephone intermediary devices using an Extech 407780A sound-level meter. The sentences were produced by a Logitech loudspeaker placed at a 0° azimuth, with noise coming from 4 other Logitech speakers oriented at 70°, 140°, 210°, and 280° relative to the primary loudspeaker.

Figure 5The sound recording engineers’ letter-grades are shown in Figure 5. As can be seen, the relatively poor sound quality ratings of these professional recording engineers show hearing aid telephone interface devices generally do not provide high-fidelity sound to the person listening on the other end when the hearing aid user is calling in a noisy environment.

It is also of interest to measure speech recognition for the hearing aid user when using these various telephone intermediary devices. To this end, the fourth author (Carrie Rector) used 5 different telephone interface devices while listening to AZ Bio sentences. The test sentences came from a landline phone placed in another room. The Az Bio Sentences were presented at a 65 dB SPL at a +5 dB SNR as measured at the mouthpiece of the landline telephone. The Logitech speakers were placed at the same 0°, 70°, 140°, 210°, and 280° azimuths. She wore each of the applicable intermediary devices corresponding to the manufacturers’ hearing aids, and the aids were programmed to an NAL NL-2 target for 55, 65 and 70 dB SPL outputs based on her hearing loss.

Figure 6

 

 

 

 

As Figure 6 demonstrates, these manufacturers’ wireless interface devices do not provide equal speech recognition on the telephone for this listener. Consistent with these findings, the fourth author noted that she could not comprehend the sentences without guessing, except when wearing the hearing aid/telephone interface devices denoted as Systems 3 and 5 in Figure 6.

Of particular note in Figures 5 and 6 are the favorable sound quality ratings and word recognition scores obtained with System 5. This device transmits directly from an iPhone to the hearing aid with no intermediary device. It is suspected that the improvement in sound quality scores from the sound engineers with this device may be due to having one less data compression system—namely the intermediary device. Specifically, when an intermediary device is inserted between a Bluetooth-enabled phone and a hearing aid, the speech signal is compressed twice. First, the signal is compressed by the intermediary device, and then the transmission from the intermediary device to the Bluetooth enabled phone compresses the signal a second time.

These results also support the recent call for the establishment of sound quality and fidelity standards in wireless streaming hearing devices.60

3) Communication Limitations Not Amenable to Solutions via Wireless Connectivity in Hearing Aids

Wireless connectivity in hearing aids is not a panacea for all communication problems experienced by people using hearing aids. It is important for the hearing care professional to remember that, while wireless technology may dramatically improve communication in a variety of listening situations, there are numerous factors that may decrease the benefit of any wireless interface device.

For example, hearing aids that are under-fit can dramatically compromise word recognition, even when an external microphone is being used. Leavitt and Flexer61 showed that premium-level hearing aids cannot overcome communication problems in noise when these aids are under-fit relative to a well-established target. This problem of hearing aid under-fitting is compounded as the original default program of the hearing aid is typically the program used for wireless transmission. As such, it is possible that, even with the aforementioned advantages potentially provided by a remote microphone or a telephone interface device, insufficient gain provided in the default program will likely compromise the hearing aid user’s speech recognition.

In addition, patients with unrealistic hearing aid expectations, phonemic regression, central auditory processing problems, Auditory Neuropathy Spectrum Disorder, hearing aid use problems, hearing aid feedback issues, and/or cognitive problems may experience communication problems even when appropriate hearing aid targets have been achieved and wireless technology is working optimally.

While many of the aforementioned factors compromising hearing aid/wireless device benefit are outside the hearing care professional’s control, we can assure that appropriate amplification has been achieved through real-ear measures. Further, we can ascertain that wireless technology is not only functioning properly, but the hearing aid user is skilled in the manipulation of such technology.

Our ongoing goal must be to provide as much auditory information as possible to the brain of the person with hearing loss, in all listening environments. Achieving this goal requires a real-ear verified hearing aid output, a high fidelity wireless connection, and the skilled use of hearing aids and wireless technology by the end user.

As Cox, Johnson, and Xu62 noted, audiologists should focus on patient-centered training and appropriate individualized hearing aid programming. It is folly to assume that simply choosing hearing aids based on premium features and wireless connectivity will optimize speech intelligibility outcomes for our patients.

In short, wireless connectivity in hearing aids is a powerful tool that offers significant communication improvement for hearing aid users. Such improvement can only be achieved when the end user is skilled in the use of wireless technology and the hearing care professional has opened the doorway to the brain to the greatest extent possible. This is achieved through real-ear verified hearing aid programming, sufficient hearing aid use instruction, and description of the benefits and limitations of hearing aids and wireless technology.

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Leavitt et al

 

Correspondence can be addressed to HR or Dr Leavitt at: [email protected].

Original citation for this article: Leavitt RJ, Flexer C, Clark N, Rector C. Unraveling the Mysteries of Wireless Connectivity in Hearing Aids. Hearing Review. 2016;23(9):14.?