Starkey Research & Clinical Blog

Understanding the best listening configurations for telephone use when wearing hearing aids

Understanding the best listening configurations for telephone use when wearing hearing aids

Picou, E.M. & Ricketts, T.A. (2010) Comparison of wireless and acoustic hearing aid based telephone listening strategies. Ear and Hearing 31(6), 1-12.

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

Telephone use is an important consideration for hearing aid users. It is often challenging to arrive at the appropriate coupling method to the ear and related hearing aid settings. Many people with hearing loss have difficulty hearing on the telephone and concerns about telephone use may result in reluctance to purchase new hearing aids or to use aids that have already been purchased (Kochkin, 2000).  Indeed, in a survey of hearing aid satisfaction, one in five respondents reported dissatisfaction when using the telephone with a hearing aid (Kochkin, 2005).

There are a number of factors that affect a hearing aid user’s ability to hear on the phone, including lack of visual cues, reduced bandwidth, background noise and difficulty coupling the phone to the hearing aid. The lack of visual cues has been addressed recently with videoconferencing applications, but these are not commonly used, especially among older individuals. The reduced bandwidth (approximately 300 to 3,300 Hz) is characteristic of sound transmission over the phone, so there is little an individual can do improve the availability of high frequency speech cues over the phone. Background noise and coupling issues can be addressed in a number of ways, depending on the individual and the circumstances.

There are two ways a hearing aid can be coupled directly to the telephone; acoustically and with an inductive telecoil  or with acoustic settings that focus on the telephone’s limited frequency range. A drawback to the acoustic setting is that the hearing aid microphone is active which may result in feedback (Latzel et. al., 2001; Palmer, 2001; Chung, 2004).  Despite recent improvements in feedback control, this remains a problem, especially for those with severe hearing loss whose hearing aids require more gain.  Additionally, the microphone picks up environmental noise that competes with the telephone signal, decreasing the signal to noise ratio.  Telecoils can be a solution for feedback and poor signal to noise ratios, but they are subject to interference from fluorescent lights, computer equipment and power lines.  Furthermore, it can be difficult to determine the proper positioning of the phone for optimal sound quality, as the telephone receiver must be placed as close to the telecoil as possible (Tannahill, 1983; Compton, 1994; Yanz & Preves, 2003).

A recent option for telephone is through the use of intermediate wireless accessories, these route sound from the phone to the hearing aids via a combination of Bluetooth and a direct-to-hearing aid wireless technology. These devices address the problems with acoustic or telecoil coupling, and have the possibility of providing some additional benefit if the telephone signal is bilaterally routed (Green, 1976; Moore, 1998; Hall et al, 1984; Quaranta and Cervellera, 1974).  Many hearing aid manufacturers offer wireless devices, but it is unclear whether their use results in significantly improved speech recognition over the phone. Even with wireless routing of the phone signal, there may still be detrimental effects of background noise, especially for individuals with open-canal hearing aids (Dillon, 1985; 1991).

The purpose of Picou and Ricketts’ study was to examine speech recognition performance with monaural and binaural wireless phone transmission, as well as a monaural acoustic condition, in the presence of two levels of background noise. They also evaluated performance with occluding versus non-occluding domes.

Twenty individuals with sloping, high-frequency, sensorineural hearing loss participated in the study. Subjects were fitted with binaural, receiver-in-canal hearing instruments with a wireless transmitter accessory. Half of the subjects were tested with open, non-occluding domes and half were tested with closed, occluding domes.

A total of seven hearing aid and telephone configurations were tested in two background noise levels (55dBA and 65dBA). Subjects responded to sentences from the Connected Speech Test (CST, Cox et al., 1987).  Speech stimuli were band pass filtered from 300 to 3400Hz to simulate telephone transmission and presented at 65dB.  Competing speech babble was presented through four loudspeakers positioned around the listener at a distance of 1 meter. All test conditions – hearing aid condition, dome type, noise level – were counterbalanced to avoid effects of learning and fatigue.

This study illuminates some important considerations in telephone use and supports the use of wireless telephone accessories, especially with bilateral routing.  The participants subjects performed best with external hearing aid microphones turned off, but the authors acknowledge that for safety and monitoring of environmental sounds, it may be advisable to leave microphones active at an attenuated level. The authors suggest that further investigation is warranted to determine optimal levels of microphone attenuation to allow for successful speech recognition over the phone, while preserving environmental awareness.

Performance with occluding domes was better than open domes for wireless telephone signal routing in noise. Occluding domes reduce the environmental noise entering the ear canal, providing an improvement in signal to noise ratio. In the acoustic phone condition, open domes performed better than occluding domes. Subjects tended to position the phone directly over the ear canal which likely improved signal to noise ratio by blocking background noise and isolating the speech transmitted from the phone.

Specific observations were made for participants wearing open-canal hearing aids. Specifically, users with open domes should be instructed to hold the phone directly over the ear canal for optimal speech recognition. Programming adjustments may be necessary to increase availability of low and mid-frequency speech cues and improve signal to noise ratio.  Conversely, users with occluding domes should be advised of the potential limitations of direct acoustic coupling to the phone and should be instructed to hold the phone receiver as close to the microphone as possible. Alternatively, patients with occluding domes may be better off using a telecoil, if available, for situations in which they cannot use a wireless device.

Interestingly, the no significant improvement in speech recognition resulted from plugging the non-test ear or muting the hearing aid on the non-test ear.  This is consistent with previous research on masking level differences for tones (Green, 1976; Moore 1998) as well as a previous study of speech recognition over the phone, which found no improvement for normal-hearing listeners when the non-phone ear was plugged.  This is inconsistent, however, with reported preferences of hearing aid users.  Despite the lack of improvement in the current study, the authors acknowledged that muting the hearing aid on the non-phone ear may reduce listening effort, which is therefore preferred by the listener.

For users of wireless accessories, the results of this study clearly indicate that binaural routing is ideal. But for hearing aid users who do not have wireless devices, the optimal hearing aid settings and coupling method may depend on several factors. The extent of venting or openness should be considered when choosing an acoustic phone coupling; individuals with minimal venting may not hear well unless they are able to hold the telephone over the hearing aid microphone, while patients with open fittings may experience more challenges with background noise interference than the more occluded wearer.

Regardless of whether a client uses an intermediate wireless device for binaural telephone streaming, monaural acoustic listening or telecoil coupling, the attenuation level of the hearing aid microphones is also a consideration. For binaural wireless routing or streaming it is advisable to keep both hearing aid microphones active but attenuated, to preserve awareness of environmental sounds. For monaural acoustic/telecoil combinations the microphone level on the opposite ear can be attenuated slightly to allow environmental awareness but reduce distraction from surrounding noise. As noted earlier, further study is warranted to determine optimal microphone attenuation levels.


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