Part 4: Addressing temporal processing deficits via ALDs, environmental modifications, and training

Vishakha W. Rawool, PhD,
is a member of the faculty in the Department of Speech Pathology and Audiology at West Virginia University, Morgantown, WVa.

Applying basic science regarding temporal processing to clinical services involving hearing instrument dispensing.

In three previous articles, various aspects of temporal processing1 and effects of hearing loss on temporal processing2 were reviewed. In a companion article, which appeared in last month’s HR, a review of amplification strategies that have been used to compensate for temporal processing deficits was provided.3 This final article of the series discusses strategies related to assistive listening devices, environmental modifications, and training that can be used to address patients’ temporal processing problems.

Using ALDs to Address Temporal Processing Deficits
Poor gap detection, poor separation of speech and noise sources, poor inter-aural time-difference discrimination, and poor masking level differences can all lead to difficulty in understanding speech in background noise in the presence of hearing loss.1-2 Assistive listening devices (ALDs) can deliver a much cleaner temporal signal to the ear that is relatively free from noise and reverberation.

A variety of assistive listening devices are available, including induction loop systems, infrared devices, FM systems, and Bluetooth devices. The FM and Bluetooth devices transfer the signal to the listener’s ear through radio-frequency waves, can travel through walls, and are not affected by sunlight. Therefore, it can be argued that these devices offer greater flexibility over induction loop and infrared devices.

FM systems: Frequency modulation (FM) devices can improve the signal-to-noise ratio (SNR) by 12 dB to 18 dB over conditions in which only the hearing aid is used.4 However, clients are often reluctant to purchase this technology due to cost or cosmetic issues.  

In the past, those individuals who purchased the technology due to lack of cost concerns or due to severity of hearing loss or communication difficulties were usually excited initially and offered comments such as “it is so much easier now to communicate with my wife while driving the car or in a restaurant.” This initial excitement usually diminished over time resulting in minimal or no use of the FM device.

The most likely reasons for this were interference from other signals, frequent need for charging or replacing the rechargeable batteries, cosmetic concerns, and the need for the transmitter to be closer to the speaker’s mouth. For example, over time, listeners became acutely aware of the fact that, although they could easily listen to their wife or significant other in a noisy restaurant, they continued to have difficulty understanding what the waiter was saying.  

Modern FM devices are highly sophisticated and incorporate digital noise control and directional microphones.

Bluetooth devices. Some products incorporate Bluetooth technology to allow wireless communications with Bluetooth-compatible mobile phones. Such technologies can allow significant improvements in speech understanding when using a cell phone.5

The Bluetooth chip provides a way for exchanging information between different devices, such as personal digital assistants (PDAs), digital cameras, and mobile phones via secure, relatively low-cost, globally available short-range radio frequencies. It uses a fast, frequency-hopping technique to provide clear, noise-free exchange of signals between devices. Signals hop 1,600 times per second between frequencies and correct errors to ensure accurate transfer of information.

It is easy to establish communication between paired Bluetooth devices without interference from other nearby Bluetooth devices. The battery drain is minimal because Bluetooth uses only 1/100th of the power level of a cell phone.

Digital Bluetooth ALDs are currently available that include a transmitter and a stock receiver that hooks over the pinna or a receiver attached to the listener’s hearing instrument.6 

Loop systems. Hearing aids that contain telecoils allow the users to be seated anyplace in the area covered by the system. Should the hearing aid user not have a hearing aid equipped with a telecoil, a magnetic receiver and earphones can be supplied or purchased by the venue. Several recent articles7-10 have pointed out the many attractive features of these systems, and why telecoil use should be expanded to all hearing aids.

However, the cost and inconvenience of installing an inductive loop system under carpeting or above ceilings have generally thwarted the greater use of these devices in public venues, and the average hearing aid user’s knowledge that these systems even exist is still lacking. In this latter respect, the United States lags far behind Europe in the provision of the systems.9 Large-area loop systems are also subject to electromagnetic interference, and some telecoils may suffer from poor sound quality.

IR systems. Infrared (IR) group hearing systems became the popular—and economical—choice for most auditoriums, churches, and school rooms. The receiving units (which rely on batteries) are handed out at the front desk or by an usher. However, these systems are often ineffective in sunlight or in bright artificial light, and they are usually underutilized due to lack of knowledge on the part of potential users that the systems exist. There is also a reluctance by some to identify their need for hearing help to the patrons (eg, too much hassle in obtaining and returning the IR units).

ALD Technology and Health
Some patients may raise the issue of damage from radio frequency waves with the use of Bluetooth technology since similar issues have been raised with the use of cellular phones. Heating or cooking by means of radio frequencies is possible over a broad frequency range. This is achieved in microwave ovens by using very high powered concentrated beams (up to one million times greater than the power output of Bluetooth transmitters). However, ALDs use technologies that are relatively safe from these concerns.

The maximum increase in brain temperature through the use of a mobile phone is 0.1ºC. Although the use of cellular telephone may be associated with a low risk for high-grade glioma, overall results do not support an association between use of cellular telephones and risk for glioma or meningioma12 (further studies are evaluating the effects of long-term use). However, the transmitting power of a Bluetooth device is far too weak to result in detectable effects in humans. In addition, the radiation is not concentrated in a single beam; it is randomly dispersed in all directions. The penetration depth of a device working in the 2.4 GHz frequency range is about 1.5 cm, which suggests only superficial absorption.

It is even possible that nanotechnology can be used to keep future hearing aid shells cool and unaffected by the radio-frequency energy. Using tiny particles (100 nanometers), one hearing aid manufacturer has already developed an ultra-thin, anti-adhesive nanocoating that repels water, sweat, and other adherents.

Promoting the Use of ALDs
The following improvements in current technology can promote the use of ALDs:

1) Automatic, dynamic switching of the microphone from directional to omnidirectional mode when speech signal from a different direction (eg, waiter) is detected in the immediate environment of the listener.

2) Availability of cosmetically discrete microphone arrays that can be camouflaged as pens, decorative pins, collars, shirt-buttons, etc.

3) The fact that some customers still prefer CICs over open-canal BTEs due to cosmetic reasons11 cannot be ignored. Thus, CIC aids that have FM receivers or Bluetooth chips should be made available when technology allows it. The hearing aids should automatically switch from the microphone to the Bluetooth mode or to the telephone mode based on the signal input.

4) The power-requirements in current assistive listening devices need to be greatly reduced or the batteries used in powering the instruments need to have a very long life. Such long-lasting batteries are currently used in middle ear implants.

With the advent of nanotechnology, Bluetooth, and the incorporation of these technologies in hearing aids, all of the above improvements are becoming possible or at least plausible. (Nanotechnology, or molecular manufacturing, deals with the design and manufacture of exceptionally miniature electronic circuits and devices from single atoms and molecules.)

Environmental Modifications
The poor ability of individuals with hearing loss to fuse the direct sound with early reflections of that sound and poor tolerance of speech with temporal asynchrony predicts poor speech recognition in the presence of reverberation. In addition, poor gap-duration discrimination is also associated with difficulty in resolving the variable temporal fluctuations in the reverberant speech waveform.

Many acoustic environments tend to be noisy and have high reverberation. For example, in some senior centers, announcements made over the speakers are difficult to understand even for listeners with normal hearing. These environments are often not carpeted due to the fear of mold and the on-going cost involved in cleaning the carpets on a regular basis. The existing PA systems have distortions; the number of speakers and the speaker location is often inadequate. Acoustic tiling is not available especially when the center is located in old buildings or houses. Perhaps the hearing industry could take a lead philanthropic role in modifying these environments by providing acoustic ceilings or mold-free carpeting, rearranging the location of loudspeakers, etc, to make them listener-friendly, which will be beneficial to both listeners with normal hearing and those with hearing loss.  

Training
Much of the temporal processing predominantly occurs at the cortical level. Thus, temporal processing skills can be enhanced by auditory training focused on capitalizing neuroplasticity. For example, providing high frequency information can help in detecting temporal modulations at higher rates or understanding fast speech.

However, ensuring the audibility of high frequency information does not assure that such information will be effectively used by the listener.13 Auditory training may be necessary for using the information effectively. Auditory training also has the potential to improve neural timing in the brainstem.14

Improved cognition. Individuals with better cognitive skills appear to derive greater benefit from temporal variations in background noise when listening via compression with fast time constants, which can facilitate listening to speech during the gaps of noise.15 Thus, training designed to improve cognitive skills16 may also improve speech recognition.

Good memory and reasoning skills are helpful in guessing what is not heard or those parts of speech that are partially heard. Similarly, deficits in understanding rapid speech can be minimized by providing training that is specifically designed to improve speed of processing. One study indicates that 87% of individuals can show improvement in visual processing speed, 74% can show improvement in reasoning ability, and 26% can show improvement in verbal episodic memory with training.17 

During auditory duration discrimination tasks, the auditory attention and short-term memory sites in both frontal lobes and right parietal lobe are activated,18 suggesting that—in addition to memory exercises—training targeted to improve auditory attention may also be helpful.  

Interactive computerized training programs. Interactive computerized training programs can be used for those listeners who have poor speech recognition. Listening and Communication Enhancement (LACE)19,20 is an example of such a program. It includes training geared towards improving the perception of time-compressed speech and speech in background of noise, improving auditory memory and speed of processing, and improving the use of communication strategies. A pilot study with the system suggests that listening skills can be enhanced through such training.

Datalogging and automatic switching in auditory training. When individuals with hearing loss are provided initially with hearing instruments, they are informed that they should first wear their hearing aids in quiet surroundings, and after they get used to listening in quiet surroundings, they should begin to use the hearing instruments in noisy surroundings.  

The above instruction is often not followed, especially by some older individuals. Such individuals often do not use their aids at home, as the significant other is used to talking loudly and the television volume is set at a high level, which eliminates the need for hearing aid use. In fact, many older individuals purchase hearing aids just before a major event, such as Christmas, a graduation party, or wedding. All these events usually involve noisy settings that might be viewed as the worst possible environment for the initial use of a hearing aid.

As a result, the hearing aid is initially used outside the home in noisy surroundings without any use in quiet surroundings, which results in an unsatisfactory experience. The hearing aids are then either kept in the drawer or are promptly returned. Recent studies also show that hearing aid rejection is related to a lack of background noise acceptance while listening to speech.21

The initial use of hearing aids should occur in quiet surroundings for at least two reasons:

1) Hearing aid use in quiet allows the listener to experience an easy listening situation. For success, any training—including listening training—should progress from easy to difficult stimuli (eg, not doing this is akin to throwing the patient into the deep end of the pool in order to learn how to swim). The use of hearing aids in quiet can allow the listener practice in listening to the newly frequency shaped signal.  

2) Initial listening in quiet situations can provide a relatively steady or stable signal that is not affected by degradation due to noise or altered by adjustments made by the new digital aid to reduce noise. For example, in a noisy situation, the hearing aid may alter the speech-signal further if it detects more noise in certain frequency bands.

It is possible that new datalogging and automatic switching capabilities can be used to make the hearing aid initially transparent in noisy surroundings without providing any gain until the data indicate that the hearing aid has been used in quiet surroundings for specific number of days or hours. After using the hearing aid in quiet, the devices can then switch to providing amplification first in moderately noisy surroundings, and then later in all noisy surroundings. Of course, the individuals need to be informed that the hearing aids will not function in noisy surroundings until they have been used sufficiently in quiet surroundings. This system might be analogous to some manufacturer fitting protocols that have been designed to “ease” patients into amplified sound by using successively greater amounts of gain.

Limiting initial hearing aid use to quiet surroundings will provide natural auditory training for listening to speech shaped by the hearing aid. Progressive exposure to noisy surroundings may help in improving tolerance of the background noise over time and aid in better speech recognition in noisy surroundings by capitalizing natural auditory training that progresses from easier to harder listening conditions. For most listeners this type of listening practice may be sufficient to improve speech intelligibility.

Caveat on datalogging. Some individuals may perceive data-logging as “spying on their personal auditory life-styles” or not allowing them to use their aid the way they would like to use it. Proper initial counseling and explanation about datalogging and the advantages of obtaining data can minimize the possibility of future concerns. 

Individually tailored auditory training. For those listeners who have severe deficits in speech recognition, one approach to providing auditory training is to analyze the errors made by the individual in quiet and noisy surrounding while wearing the hearing aids. Phoneme inventories can be used for this purpose.

The phoneme inventories contain a fair sample of the speech-sound combinations found in everyday speech. In addition, all the phonemes of American English appear in these lists in various vowel consonant relationships.22 After determination of specific confusion errors made by the listener, training can be specifically designed to reduce the listening problem that occurs (for example, perceiving “far” as “par”).  

Another possibility is to provide training for improving specific deficits, such as deficits in duration discrimination or gap-duration discrimination. Transfer of the benefit from such training should be promoted by providing practice for listening to various speakers in a variety of contexts and variety of listening environments.

Summary
In the presence of severe deficits in recognizing speech, ALDs may be the best way of delivering a clean temporal signal to the ear. Cosmetically appealing transmitters and receivers and long-lasting batteries may also one day promote the use of these systems. Environmental modifications to minimize reverberation can also be very helpful.

Lastly, the benefit of training for improving speed of processing and cognition combined with auditory training cannot be ignored. Auditory training or practice in listening to processed speech is especially important when special algorithms are used to address specific deficits. Auditory training through natural exposure to increasingly difficult daily sound environments can also be managed through appropriate hearing aid encoding incorporating modern datalogging and automatic switching capabilities.

References
1.   Rawool VW. A temporal processing primer. The Hearing Review. 2006;13(5): 30-34.

2.   Rawool VW. The effects of hearing loss on temporal processing, Part 2: Looking beyond “simple audition”. The Hearing Review. 2006;13(6): 30-34.

3.   Rawool VW. The effects of hearing loss on temporal processing, Part 3: Addressing temporal processing deficits through amplification strategies. The Hearing Review. 2006;13(7):30-38.

4.   Lewis MS, Crandell C, Valente M, Enrietto Horn J. Speech perception in noise: directional microphone versus frequency modulation (FM) systems. J Am Acad Audiol. 2004;15:426-439.

5.   Tchorz J, Schulte M. Utilizing Bluetooth for better speech understanding over the cell phone. The Hearing Review. 2005;12(2): 50-51,80.

6.   Yanz JL. The Future of Wireless Devices in Hearing Care: A technology that promises to transform the hearing industry. The Hearing Review. 2006;13(1): 18-20,93.

7.   Ross M. Telecoils: The powerful assistive listening device. The Hearing Review. 2002;9(9):22-26,57.

8.   Ross M. Telecoils are about more than telephones. Hear Jour. 2006;59(5):24-28.

9.   Myers DG. Heard around the world! Hearing aid compatibility and wireless assistive devices. The Hearing Review. 2005;12(1): 22-25,86.

10. Myers DG. In a looped America, hearing aids would be twice as valuable. Hear Jour. 2006;59(5):17-23.

11. Otto WC. Evaluation of an open-canal hearing aid by experienced users. Hear Jour. 2005; 58(8):26-32.

12. Collatz CH, Schuz J, Kosteljanetz M, Poulsen H Skovgaard, Boice JD Jr, McLaughlin JK; Johansen C. Cellular telephones and risk for brain tumors: a population-based, incident case-control study. Neurology. 2005;64(7): 1189-1195.

13. Turner CW, Robb MP. Audibility and recognition of stop consonants in normal and hearing-impaired subjects. J Acoust Soc Am. 1987;81: 1566-1573.

14. Russo NM, Nicol TG, Zecker SG, Hayes EA, Kraus N. Auditory training improves neural timing in the human brainstem. Behav Brain Res. 2005 156(1):95-103.

15. Gatehouse S, Naylor G, Elberling C. Benefits from hearing aids in relation to the interaction between the user and the environment. Intl J Audiol. 2003;42:S77-S85.

16. Gunther VK, Schafer P, Hlozer BJ, Kemmler GW. Long-term improvements in cognitive performance through computer-assisted cognitive training. A pilot study in a residential home for older people. Aging Ment Health. 2003;7(3): 200-206.

17. Ball K, Berch DB, Helmers KF, Jobe JB, Leveck MD, Marsiske M, et al. Effects of cognitive training intervention with older adults: a randomized controlled trial. JAMA. 2002;288(18):2271-2281.

18. Pedersen CB, Mirz F, Ovesen T, Ishizu K, Johannsen P, Madsen S, Gjedde A. Cortical centres underlying auditory temporal processing in humans: A PET study. Audiology. 2000;39(1):30-37.

19. Sweetow RW, Henderson-Sabes J. The case for LACE: Listening and auditory communication enhancement training. Hear Jour. 2004;57(3): 32-40.

20. Sweetow RW. Physical Therapy for the ears: Maximizing patient benefit using a listening retraining program. The Hearing Review. 2005;12(10): 56-58.

21. Nebelek AK, Tampas JW, Burchfield SB. Comparison of speech perception in background noise with acceptance of background in aided and unaided conditions. J Sp Lang Hear Res. 2004;47:1001-1011.

22. Duffy JK, Zelnick E, Zelnick M. Marketing hearing rehabilitation. The Hearing Review. 2005;12(3):26-33.

Correspondence can be addressed to HR or Vishakha W. Rawool, PhD, Dept of Speech Pathology and Audiology, West Virginia University, PO Box 6122, Morgantown, WV 26506-6122; e-mail: [email protected]