In October 2004, Siemens Hearing Instruments introduced a new product, ACURIS™ with e2e wireless™ technology. We believe that this wireless hearing instrument technology, the first of its kind available in the hearing industry, has opened new roads in the future of product development. In this article, we respond to some commonly asked questions concerning this new product.

What do you mean by e2e wireless?
As you might guess, e2e refers to “ear-to-ear.” That is, there is wireless communication between the right and left hearing instruments while they are worn. Both hearing instruments send and receive signals from the other. During normal operation, both hearing instruments are continually sharing information about the current environment and control settings.1 The use also can trigger additional information transmission through user controls.

Is this information transmitted through FM technology?
No. A more efficient manner to conduct information sharing between hearing instruments is the use of electromagnetic transmission. Acuris has a transfer rate of 215 bits/second and sends coded digital information alternating on two frequencies, 114 kHz and 120 kHz. This form of modulation is called Frequency Shift Keying (FSK). Operating on this narrow frequency band assures that e2e wireless functions virtually free of interference.

Although FSK modulation is used in Bluetooth-enabled applications, the form of electromagnetic transmission used in Acuris devices is not defined as “Bluetooth.”

Is e2e like a wireless CROS or BiCROS system?
No. This system is designed for people with hearing loss in both ears appropriate for hearing instruments as opposed to people with unaidable hearing in one ear. Unlike the CROS configuration, input signals are not transmitted to the other hearing instrument. With e2e wireless, each hearing instrument independently processes and amplifies its own input. What is transmitted between hearing instruments is information and directives to enable or disable advanced sound processing features.

Is it safe to have this continual energy transmission around the head?
It definitely is safe and we have studied this topic carefully. First, it’s important to point out that all electronic devices—dishwashers, televisions, telephones, etc—produce electromagnetic fields. Relative to amplification, FM systems and cochlear implants also produce electromagnetic fields. The intensity of the electromagnetic field of the e2e wireless system is very low and has been measured and declared below safety limits for the United States and all other countries where Acuris is registered and sold. For example, sitting 1 meter (approximately 40 inches) away from a halogen lamp for 4 hours is equal to the exposure of wearing ACURIS with e2e wireless for more than 10 hours a day for an entire week. Or, working 1 hour at a distance of 20 inches in front of a computer monitor is equal to wearing the device with e2e wireless for 10 hours a day.

Detailed technical and safety information (including measurement data) is provided in a brochure called e2e Wireless Technical Guide and is available upon request.

What are the expected patient benefits of binaural wireless?
There are many. We can start by discussing the ability of the hearing instruments to share information regarding classification of the environment. In most modern hearing instruments, digital noise reduction works as channel-specific gain reduction. Gain reduction occurs when the hearing instrument, based on its acoustic analysis of the incoming signal, determines that the signal is noise, not speech.2 Most hearing instruments can do this quite effectively when analyzing an environment with a single talker in quiet, or in an environment with steady-state noise and no speech present. However, when speech and noise are mixed, which is often the case, correct identification becomes more difficult. With Acuris with e2e wireless, the classification of the incoming signals is based on the acoustic analysis from both hearing instruments together. Since more information is used in the decision-making process, it increases the likelihood that the correct decision will be made.

Is the implementation of noise reduction also synchronized?
Yes, and we believe this is an important patient benefit. With unilateral decision-making, one hearing instrument might be using different digital processing than the other, or using different timing characteristics. With e2e wireless, the noise reduction activation algorithms are linked so they reach the same signal processing characteristics, at precisely the same time.

Does the bilateral environmental classification control other features?
It also is used to assist in controlling the automatic feature of the directional technology. The Acuris has an automatic directional feature: that is, when certain environmental conditions exist, it transitions smoothly from omnidirectional to directional mode, and vice versa.3,4 One of the algorithm rules governing the transition is whether the primary signal is speech or noise. So again, the wireless communication assures that both hearing instruments will transition at the same time. The patient wouldn’t be in a situation where one hearing instrument was in directional mode, and the other set to omnidirectional mode.

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The Acuris MCs (Mini-Canals, left) with push button and volume control, and (right) Acuris P BTEs. The e2e wireless system makes it possible to control both the left and right hearing instruments with one control for volume and one for program selection. The two hearing instruments are designed to work together as a single, unified system in a binaural fitting, transmitting data between the individual aids.

Does it matter if both hearing instruments are in the directional mode?
Yes, and there is research that says it does. Recently, Hornsby & Ricketts (“Benefits of bilateral use of directional hearing aids,” unpublished data, 2004) conducted the HINT for hearing-impaired subjects in a diffuse sound-field in mild reverberation. Their results showed that there was a 40% improvement in benefit (using the bilateral omnidirectional condition as the baseline) when the subjects had both hearing instruments set to directional compared to when only the right or left hearing instrument was in the directional mode.

Is compression also linked with e2e wireless?
No. We know that nearly all patients have some degree of asymmetry in their hearing loss and loudness discomfort levels between ears. Our fitting methods are designed to compensate for this asymmetry by using different kneepoints and ratios for the AGCi (WDRC) and different kneepoints for the AGCo. This is accomplished across 16 channels of compression to remap important acoustic information into the patient’s residual dynamic range.

Because there is unaided asymmetry, we want compression to act unilaterally independent to account for these dynamic range differences and attempt to obtain aided loudness symmetry. We then use wireless technology to control the bilateral functionality of other features.

What are the other benefits of wireless transmission?
A feature that has been heralded by nearly all hearing instrument users is the bilateral alteration of gain using only one control. In other words, the patient can reach up to his right ear (or left ear), and by changing the volume control (VC), he/she can turn the gain up or down for both ears simultaneously. This allows users to make adjustments more discreetly, and obviously, there is only 50% of the effort required for this operation. While all patients appear to like this feature, it is especially helpful for those individuals who have dexterity problems.
Beyond “ease of use,” are there audiological reasons why bilateral control of gain is desired?

We know that there are many advantages to binaural hearing, but some of these advantages are not always realized in a bilateral hearing instrument fitting. A fitting can be bilateral, without providing significant binaural benefit.

One potential binaural advantage is localization, which is based on interaural intensity and timing cues. We assume that when hearing instruments are fitted, it is verified that the patient experiences aided “loudness balance” for different input levels, which will facilitate aided localization. If patients have hearing instruments with VCs, however, they easily can disrupt this balance, and recent research has shown that this does happen (B Hornsby & T Ricketts, “Hearing aid user volume control adjustments: Bilaterial consistency and effects on speech understanding,” unpublished data, 2004). While patients might learn to localize to a consistent mismatch,5 when patients do not adjust their VCs equally, the interaural loudness differences could change several times a day.

With wireless synchronization, gain changes are applied equally to each hearing instrument. In fact, even if the hearing instruments were not balanced at the time of the fitting, the patient will at least continue to experience a consistent loudness mismatch when gain is changed.

Is localization that important?
Appropriate localization allows the user to experience a more “normal” listening environment. Not knowing where a sound is coming from can be disturbing, and can influence concentration on speech understanding. In extreme cases, poor localization could be a safety issue. Finally, good localization will help the hearing aid user follow the talker in a group conversation. This has the potential to improve speech intelligibility indirectly due to speech reading and directional microphone orientation.

Are there other advantages to synchronous gain adjustments?
Possibly. In noisy or reverberant environments, we know that people hear better with two earns than with one. There is a well-known principle known as the “squelch effect” that is related to the brain’s ability to use binaural sound-level or binaural masking level differences, which we know applies to bilateral hearing instrument use.6 We expect an improvement of about 3 dB in signal-to-noise ratio (SNR) for bilateral fittings compared to a unilateral fitting, which can equate to 30% or more improvement in intelligibility for some speech-in-noise listening situations. In studies of the masking level difference, it has been shown that the squelch effect will be reduced when asymmetry is present.7

It’s also possible that aided symmetry will assist in maintaining binaural summation, which often is 6-10 dB at supra-threshold levels. Maintaining summation is important, as this allows for reduced gain, which increases headroom and reduces feedback problems. In general, we want to avoid asymmetry, as this might reduce patient benefit and satisfaction.8,9

What other user controls are synchronized?
The program memory button also can be synchronized—a feature that has been well received by users. As with gain, one button controls the programs for both hearing instruments. If, for example, you have selected a “restaurant” program for memory #2, the push of a button on just one side shifts both hearing instruments to this program. Or, if the patient prefers, both gain and program selection can be conducted with a remote control.

f04a.jpg (8467 bytes)The ePocket remote control.

So the system also can be used with a remote control?
Yes, Acuris is available with an optional remote control called ePocket™. In addition, ePocket is the first bi-directional remote control in the industry. By bi-directional, we mean that it not only allows the patient to have control of bilateral volume and program selection, but it also has read-out functionality. This means that patients may review the status of their volume setting, memory location, and battery strength for both instruments at any time.

Can the wireless function be disabled for patients who don’t want it or for monaural fittings?
The wireless function can be disabled in the fitting software. And, it’s not an “all or none” choice; you can have some features coupled, and other features uncoupled, as desired.

Your patients also can experience the benefits of the advanced core technology features of Acuris without using the same model of hearing aid in the other ear, or he/she could be fit monaurally. A second Acuris can be added at a later date and the wireless feature can then be activated. Or, the patient could simply remain a unilateral hearing instrument user if that was appropriate.

Speaking of core technology, is that also new?
Yes, the core technology in Acuris is different from previous technologies introduced by Siemens. There are five general categories of core technology in this hearing aid: Multi-Channel Dynamic Range Compensation, Digital Speech and Noise Management, High-speed Digital Feedback Cancellation, Multi-dimensional Directional Optimization, and Precision Environmental Classification. These core technology features form the basis of the new product line and were designed for optimized patient benefits.1

What is different about the directional technology?
The directional microphone systems in Acuris really are multi-dimensional. Of course, the automatic operation is still featured, allowing the hearing instruments to transition between omnidirectional and directional modes when the environment requires this.3,4 In addition, the adaptive polar patterns are actually part of a multi-channel adaptive feature that allows the simultaneous attenuation of multiple noise sources (eg, noises originating from different azimuths around the user) in different frequency ranges. Even if those noise sources are all moving, the fast adaptive directional microphone can follow them and reduce these unwanted signals. Obviously, there would not be many situations where there would be more than one or two different noise sources within the patient’s immediate environment, but the system’s directional microphones can focus on up to four different signals simultaneously, if necessary, and apply different polar patterns for each to maximize directional effectiveness.

In addition, to ensure continued integrity of directional performance, real-time microphone matching is employed across the entire frequency response at different points. This is in contrast to other systems where only one frequency is matched, or a narrow range of frequencies is considered.

How is the feedback cancellation different from other products?
The new hearing aids employ high-speed phase cancellation to control feedback. This allows for the fitting of patients who require more gain and output, or have increased venting requirements due to high frequency, precipitous hearing loss, or occlusion problems. Because the feedback cancellation system does not require an initialization procedure, as some other systems do, it is extremely adaptive and can adjust rapidly to changes in the feedback path that occur transitionally.

In addition, this phase cancellation system is designed to detect whether the signal in question is feedback or an environmental signal—this prevents unnecessary cancellation or reduction of desired sounds, such as microwave beeps or other tonal signals. All of this advanced processing is done with minimum drain on the battery.

How have the algorithms changed relative to the listening situation?
There is more processing power, which allows for more discrete differentiation of inputs. Precision Environmental Classification is able to accurately detect and react in different ways to various situations, such as speech only, speech-in-noise, stationary noise, fluctuating noise and music.

In the past, the degree of sophistication that has been available in classification systems has not allowed for accurate detection of some signals, especially music. With this new classification system, there is much more information concerning the input signal which is taken into account as the environmental analysis is proceeding. This in-depth analysis allows music to be correctly identified and the appropriate sound processing to occur with respect to directionality, feedback cancellation, and other features.

Summary
Acuris with e2e wireless is truly new hearing instrument technology. All Acuris products are standard with the e2e wireless technology and the complete range of models is available, from Micro-CIC to Power BTE. The product represents an important first step in providing binaural benefits for patients with bilateral hearing instrument fittings.

This article was submitted to HR by Thomas A. Powers, PhD, chief research officer, and Pamela Burton, MA, director of product management at Siemens Hearing Instruments, Piscataway, NJ. Correspondence can be addressed to HR or Thomas Powers, Siemens Hearing Instruments, 10 Constitution Ave, Piscataway, NJ 08854; email: tpowers@siemens.com

References
1. Powers T, Burton P. Wireless technology synchronizes DSP and user controls for true binaural amplification. Hear Jour. 2005; In press.
2. Powers T, Holube I, Wesselkamp M. The use of digital features to combat background noise. In: Kochkin S, Strom KE, eds. High Performance Hearing Solutions, Vol 3: Hearing in Noise. Hearing Review. 1999;6(1)[Suppl]: 36-39.
3. Powers T, Hammaker V. Three microphone instrument is designed to extend benefits of directionality. Hear Jour. 2002;55(10):38-45.
4. Powers T, Hammaker V. Proving adaptive directional technology works: A review of studies. Hearing Review. 2004;11(4):46-50.
5. Byrne D, Dirks D. Effect of acclimatization and deprivation on non-speech auditory abilities. Ear Hear. 1996;17:29S-37S.
6. Ricketts T. The impact of head angle on monaural and binaural performance with directional and omnidirectional hearing aids. Ear Hear. 2000;21(4):318-28.
7. Jerger J, Brown D, Smith S. Effect of peripheral hearing loss on the MLD. Arch Otolaryngol. 1984;110:290-296.
8. Gatehouse S, Noble W. The speech, spatial and qualities of hearing scale (SSQ). Intl J Audiol. 2004;43,2:85-99.
9. Noble W, Gatehouse S. Interaural asymmetry of hearing loss, speech, spatial and qualities of hearing scale (SSQ) disabilities, and handicap. Intl J Audiol. 2004;43,2:100-114.