Tech Topic: Hearing Aids & Telephones | Hearing Review June 2014
With all the advances in hearing instrument technology seen over the past decade, the simple function of using hearing aids in combination with the telephone still proves difficult for most hearing aid users. This is problematic when understanding speech on the phone is the very reason why some end users seek amplification.
Desjardins and Doherty1 captured the ability of experienced hearing aid users to manipulate their hearing aids using the Practical Hearing Aid Skills Test (PHAST). They found that over 70% of the experienced hearing instrument users included in their trial performed unsatisfactorily on the phone. This correlates well with the hearing aid users’ self-reported success on the phone. Phone use is listed as one of the reasons why already-purchased hearing aids are not being used,2 and those making use of their hearing instruments report dissatisfaction on the phone on par with dissatisfaction ratings for hearing instrument use in large groups.3
Several factors contribute to hearing aid users’ experienced difficulties communicating on the phone. These include the absence of visual cues, inappropriate or inadequate coupling to the phone, presence of background noise and acoustic feedback, as well as positioning difficulties or constraints.
Success on the phone should be a priority for the hearing care specialist, as phone use is linked to self-reported quality of life.4 Experienced failure on the phone can translate to failure with amplification as a whole, leading to non-use and decreased benefit.
But what can the hearing care professional do to improve or optimize end-user benefit on the phone? The following sections will outline considerations that can be made for the selection and use of different telephone types/models, as well as points to cover when counseling the patient on phone use.
Optimizing Speech Understanding
Acoustic vs telecoil coupling. To ensure that the phone being used will work well with hearing aids, it is important to understand the modes in which the hearing aids operate. Hearing aids operate in one of two modes: acoustic coupling or telecoil (inductive) coupling. Hearing aids operating in acoustic coupling mode (holding the phone receiver to the hearing aid microphone) receive and amplify all sounds surrounding the user. Sounds amplified in this mode include desired sounds, such as a telephone’s audio signal, as well as unwanted ambient noise.
Hearing aids operating in telecoil coupling mode (about 60% of hearing aids contain telecoils) receive signals from magnetic fields generated by telecoil-compatible telephones. Amplification of unwanted ambient noise can be avoided in this mode by turning off the hearing aid microphones in the telecoil program. The speech intelligibility improvements offered by the telecoil will be highlighted later in this article.
Interference and handset M/T ratings. Not all phones are created equal when it comes to use in combination with hearing aids. Generally speaking, analog telephones do not pose a risk of interference and will work well with most hearing aid models.
However, contemporary landline phones generally contain digital components—which pose a risk of interference when used in combination with hearing aids. Interference can be caused by electromagnetic energy emitted by the telephone’s antenna, backlight, or other components.
The American National Standards Institute (ANSI) has created a standard outlining the compatibility of phones and hearing aids. The standard offers a rating system that the clinician and end user can use as guidance. The rating system rates a telephone for use with acoustic or microphone coupling to the hearing aid (M scale) or telecoil coupling to the hearing aid (T scale). Each scale ranges from 1 to 4. A telephone handset is considered hearing aid compatible for acoustic coupling if it meets a M3 rating; it is considered hearing aid compatible for telecoil coupling if it meets a T3 rating. Telephone handsets claiming to be hearing aid compatible will display their M and T ratings on the packaging.
In addition to rating the phones, the ANSI standard provides ratings for hearing aids from M1 to M4. On that rating scale, a rating of M1 signifies the least immune to RF interference and M4 the most immune. To find out if a particular telephone is likely to interfere with a particular hearing aid, the rating of the hearing aid is added to the rating of the telephone. A sum of 5 indicates that the telephone would provide normal use, and a sum of 6 or greater indicates that the telephone will provide excellent performance with that specific hearing aid. Landline phones designed specifically for people with hearing loss will offer an increase in loudness in the high frequencies (usually a 30 to 40 dB boost) and they will usually feature frequency and loudness adjustable ringers.
Cell phones and MFi. Most of the patients we see make use of cell phones. Cell phones offer several advantages for the hard of hearing; speaker phone, volume control, and vibrating ringer are standard in most models. Some cell phones are optimized for telecoil compatibility and most models offer Bluetooth. Cell phones can also be used to send and receive text messages, and apps can be purchased that enable captioned phone calls. An additional advantage of cell phones is the option to stream telephone conversations to the hearing aids.
One method of streaming sound from the telephone is via a hearing aid accessory (Figure 1). The accessory is paired to the cell phone via Bluetooth, and the accessory streams the conversation on to the hearing aids. This removes the reliance on correct receiver placement and offers the possibility to listen to the phone conversation in both ears.
A second method is available for the iPhone™ in the form of Made For iPhone (MFi) hearing aids (Figure 2). These hearing aids communicate directly to the iPhone via Bluetooth Smart™ technology, without the need for any intermediary device or hearing aid accessory. All sounds from the iPhone can be streamed directly to the hearing aids, including phone conversations, map directions, music, and any assistance received from Siri (the in-phone personal assistant).
The Importance of Counseling
Part of the reason why phone use and noisy surroundings are problematic is due to the patient themselves and their behaviors. When it comes to the use of directional microphones in noisy surroundings, hearing care professionals counsel patients to position themselves so the noise is behind them, the signal of interest in front of them, and to create some distance between the signal and the noise.
Such simple tactics are sometimes forgotten when it comes to phone use. Phone use tactics should be covered in detail during counseling to ensure the patient knows how to get the most out of their phone conversations.
The quality of the signal received by the hearing aid user relies on the placement of the receiver (for non-wireless streamed sounds). It is worthwhile to practice phone placement with your patients, as most do not find it intuitive to place the receiver slightly behind and above the ear (ensuring that the hearing aid microphone or telecoil is in close proximity to the telephone receiver).
Once the patient has mastered the practicalities of using the phone, there are some communication strategies that should be discussed. A great starting point is to know who is calling—either by caller ID or by simply asking. The patient should also make sure they know the subject of the conversation (eg, telephone sales, telephone survey, etc). This will make it possible to fill in any gaps by extrapolating through context.
Empower the patient to make their hearing loss known; if they hide their impairment or bluff, this can add to their experienced problems. If they are open about their impairment, they will also feel free to ask for repeats and rephrases as needed. When receiving important information on the phone, it may be necessary to ask the caller to spell out the information (ie, alpha, Charlie, tango) or count up for important numbers. The hearing aid user can also request that the caller confirm with simple yes or no answers, as these words are easier to hear when they are on their own compared to when they are imbedded in a sentence.
So, following all this optimization, how much measurable benefit can the patient expect? The following sections outline a study conducted in controlled laboratory conditions aimed at quantifying the levels of end-user benefit that can be expected when using the phone in the presence of background noise.
Subjects. Previous investigations reported in the literature found that end-user benefit with different telephone listening strategies does not change significantly as a function of hearing loss level.5,6 This informed our choice to perform testing on normal-hearing participants, thus limiting between-subject variability caused by varying levels of damage to the auditory system. A total of 10 participants with normal hearing were enrolled (4 female, 6 male).
Test setup. Testing was performed in a sound-treated room with the test participant placed in the middle of a four-loudspeaker setup (speakers at 45°, 135°, 225°, and 315° azimuth) within the critical distance of the loudspeakers. The loudspeakers delivered adaptive background noise. The following listening conditions were included:
- Acoustic phone (acoustic coupling), unilateral;
- Telecoil phone (telecoil coupling), unilateral (HA microphone on test ear Off);
- Phone Clip+ (Bluetooth) unilateral and bilateral (HA microphone on test ear Off); and
- MFi (direct sound from iPhone to hearing aids) unilateral and bilateral (HA microphone on test ear Off).
The contralateral (non-test) ear received amplification in all test conditions; amplification level in the non-test ear was attenuated by 6dB compared to the test ear.
The test materials were delivered through a landline phone receiver for the acoustic phone and telecoil test conditions (Amplipower 40, Geemarc), or streamed to the hearings aids via a hearing aid accessory (Unite Phone Clip+), or streamed directly to the MFi hearing aids (ReSound LiNX combined with iPhone 5). The hearing aids receiving the signal were ReSound Verso for the acoustic phone, telecoil phone, and Phone Clip+ conditions, and ReSound LiNX for the MFi condition. Both hearing aid models are receiver-in-the-ear (RIC) devices, and open non-occluding domes were used to couple the hearing aids to the participants’ ears. Speech level was constant for all test conditions, calibrated to deliver 65 dB SPL at the tympanic membrane.
Materials. Testing was done using Dantale II Danish speech materials7,8 in the presence of constant adaptive background noise. The speech materials were band-pass filtered beforehand to match the frequency response of a telephone transmission (ie, 300 to 3400 Hz). Background noise was a constant amplitude-modulated, speech-shaped noise signal designed to simulate 4-person speech babble.
Procedure. Each participant completed one training round at the start of the session (30 sentences), and the first 10 sentences at the start of each subsequent test round were excluded from the final score (providing some training with each condition in which the participant could optimize the telephone receiver placement for telecoil and acoustic coupling).
Speech testing, including adaptation of noise levels, was controlled through a specially designed MatLab graphical user interface. The aim of the test was to obtain speech reception threshold (SRT) information for each listening condition. A negative SRT indicates that speech was lower than the surrounding background noise. The order of test conditions for each participant was randomized using a Latin square.
Figure 3 shows the average SRT scores for each condition with high/low lines (95% confidence intervals). A larger spread in data was observed for the non-wireless conditions (acoustic phone and telecoil phone) as a result of positioning difficulties and constraints inherent to these listening methods. All conditions displayed in Figure 3 are unilateral listening. A repeated measures ANOVA with Tukey post-tests revealed that all phone listening strategies were significantly better than acoustic phone alone.
Figure 4 is derived from the results shown in Figure 3, and displays the benefit of each phone listening strategy as they compare to acoustic coupling. The telecoil phone resulted in 6 dB benefit on average. Wireless streamed sound via a hearing aid accessory operating on Bluetooth connectivity resulted in almost 9 dB benefit on average, while sound streamed directly to the MFi hearing aids resulted in 16 dB average benefit. Performance with the MFi solution was significantly better than in both the telecoil and Bluetooth streaming conditions.
Testing was also performed with the test speech materials streamed to both ears using the wireless offerings included in the study. On average, this resulted in 2 dB of additional benefit for both wireless methods.
All of the phone-specific listening strategies resulted in measurable benefit over acoustic coupling alone even when listening unilaterally. Understanding speech with acoustic coupling is problematic in the presence of background noise because the hearing aids receive and amplify all sounds surrounding the user, including the unwanted ambient noise.
The telecoil offered a reduction in amplified background noise as the hearing aid microphone was deactivated on the test ear. This benefit was maintained despite direct sound (noise) being received through the open ear canal. Performance with acoustic coupling and the telecoil was reliant on the participant’s ability to place the receiver correctly and maintain the correct placement for the duration of the test round; this resulted in a large spread in data suggesting that benefit will be variable from patient to patient.
The best performance was seen with the wireless streaming. However, streaming from the Bluetooth-based hearing aid accessory resulted in worse scores than the direct MFi streaming. It is speculated that this could be due to a decline in signal quality caused by the extra link needed when using a Bluetooth-based hearing aid accessory (phone-accessory-hearing aids). The Bluetooth protocol has been known to suffer dropouts, which could result in a decline in signal quality. The direct MFi streaming does not include any intermediary device, and the signal may therefore be more robust, resulting in the highest speech intelligibility scores for this study design.
Phone use is important for communication purposes and safety reasons, and is therefore integral to elevating quality of life for hearing-impaired individuals.
Several options exist for improving speech understanding on the phone for people with hearing loss. The hearing care professional does well to address phone use, as failure on the phone could lead to reduced benefit and satisfaction with the hearing aids as a whole.
Clinically, it is accepted that a 1 dB improvement in speech score equates to approximately a 5-10% improvement in speech understanding. Great benefit can be achieved with the use of a telecoil phone program alone (on average, 6 dB benefit was observed in this study)—a technology that is readily available in the majority of hearing aid models.
Benefit increases substantially when wireless technologies are used (on average, 8 to 16 dB benefit was observed in this study) due to the robust wireless signal, which is not affected by the positioning of a telephone receiver as well as the possibility to listen bilaterally. Time should be taken to counsel the end user on strategies for better following speech on the phone.
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2. Kochkin S. MarkeTrak V: “Why my hearing aids are in the drawer”: The consumers’ perspective. Hear Jour. 2000;53(2):34-41.
3. Kochkin S. MarkeTrak VII: Customer satisfaction with hearing instruments in the digital age. Hear Jour. 2005;58(9):30-39.
4. Dalton DS, Cruickshanks KJ, Klein BE, et al. The impact of hearing loss on quality of life in older adults. Gerontologist. 2003;43(5):661-668.
5. Picou EM, Ricketts TA. Efficacy of hearing-aid based telephone strategies for listeners with moderate-to-severe hearing loss. J Am Acad Audiol. 2013;24(1):59-70.
6.Picou EM, Ricketts TA. Comparison of wireless and acoustic hearing aid-based telephone listening strategies. Ear Hear. 2011;32(2):209-20.
7. Elberling C, Ludvigsen C, Lyregaard PE. DANTALE: a new Danish speech material. Scand Audiol. 1989;18(3):169-75.
8. Wagener K, Josvassen JL, Ardenkjaer R. Design, optimization and evaluation of a Danish sentence test in noise. Int J Audiol. 2003;42(1):10-17.
Original citation for this article: Nesgaard Pedersen, J, Kirkwood, B. Speech Intelligibility Benefits of Assisted Telephone Listening Methods. Hearing Review. 2014;21(6):18-22.