The Hearing Review Cross-Currents are staff-reviewed articles, features and news items that relate to hearing issues from a variety of sources and disciplines. If you are interested in a particular item, we encourage you to obtain a copy of the cited publication. —KES

Efficacy of 3 Commonly Used Hearing Aid Circuits, A Crossover Trial

By VD Larson et al.

While the information in what has become known in the hearing care field as the “VA Study” may by now be “old news” for those hearing care professionals who have seen presentations on it or relating to it, the fact that it appears in JAMA is reason enough for all hearing care professional to make sure that every family/general practitioner in the U.S. receives a copy of it. Quite simply, the study conducted by the Department of Veterans Affairs (VA), National Institute on Deafness and Other Communication Disorders (NIDCD) and contributing authors provides some of the best available support on how hearing instruments improve communicative ability in both quiet and noisy environments and why they represent an excellent solution for hearing-impaired people. Additionally, the study represents one of the few large-scale, multi-site double-blinded studies (i.e., both the subjects and the dispensing professionals were unaware what specific hearing instrument technologies they were using) in hearing care literature.

The study involved 360 subjects with bilateral sensorineural hearing losses in eight VA hospitals across the U.S. from May 1996 to February 1998. Subjects were predominantly male (57%), white (79%) and veterans (70%), and about half (47%) were first-time users of hearing instruments. Three hearing instrument technologies (peak clipping, compression limiting and wide dynamic range compression, all in identical shells) were provided to the subjects, so that all subjects used each instrument technology type for three months. The sequences for trying the technology types were administered in a crossover design.

Following both the initial fitting and the three-month trial, each subject was tested for speech recognition (using the NU-6 and the CST at a variety of presentation levels and SNRs using multi-talker babble), sound quality (loudness, noise interference and overall liking) and subjective benefit (PHAB). They were also asked to rank each instrument in order of preference.

The results of the study showed that all three hearing instrument types substantially improved speech recognition on the NU-6 by a total average of 29% (absolute score improvement), even though all of the aids provided reduced benefit scores on the CST as the signal-to-noise ratio deteriorated. The speech recognition improvement in noise ranged from 10-30% over the unaided condition, with better results for soft and conversational loudness levels.

As would be expected, some of the test results suggested that the compression limiting and WDRC instruments outperformed the peak clipping instrument in word recognition, loudness, overall liking, aversiveness of sounds and distortion. For example, the WDRC instrument was rated as having the most comfortable loudness compared to the other two instruments; likewise, the compression limiting instrument was rated ahead of the peak clipping instrument in comfort. However, the peak clipping instrument scored better than WDRC in noise interference.

In overall ranking, 41.6% of the subjects chose the compression limiting instrument, followed by the WDRC (29.8%) and the peak clipping (28.6%) instruments. Additionally, the compression limiting instrument was ranked third by the lowest percentage of subjects (25.4% vs. 36.2% for peak clipping and 38.4% for WDRC).

Much of the above may be essentially considered detail by people outside the hearing care field. What is most important to take away from the paper is that all three instruments provided substantial speech intelligibility and benefit over unaided conditions and demonstrably reduced the subjects’ communication problems (even in the presence of background noise). Furthermore, all three instruments did fairly well in amplifying soft and conversationally loud speech to comfortable levels, and the sound quality of the instruments was not significantly degraded.

The study should prove to be an excellent resource for the medical community and hearing care professionals. It may even serve as a bridge to demonstrate to general practitioners that hearing instruments do perform the tasks for which they are intended. Lastly, the paper demonstrates to entities like the FDA that hearing instruments also provide at least some benefit in the presence of background noise —a claim that the Agency has strongly contended in the past.

J Amer Med Assn (JAMA)
10/11/00, V284, No. 14: 1806-13

The Dominant Ear

By M Reib & G Reib

In contrast to the above landmark article, here’s one that will really “move” (or at least wiggle) the hearing care world—or at least for those people seeking archaic trivia: “In 1911, Stier reported a phenomenon which is not established even at the present time. In the asymmetrical movement of the auricals [yes, they’re talking about the ability to wiggle your ears], Stier found that more persons preferred to move the right auricle than the left. The author classified several categories: only right (4%), right more than left (19%), equal (61%), left more than right (15%) and only left (1%).” It turns out, according to Stier’s data, that right-handed people are better able to move their right auricles, and lefties are better able to move their left auricles. The author’s state “The functional importance of this form of asymmetry is unknown.” No kidding.

In all fairness, this editor believes that the authors may be having some fun in presenting the information. Additionally, they rightly point out that ear and eye dominance is a well-established sensory behavior, and what is interesting (well, ok, relatively interesting) is that “earedness” is not only a sensory but also a motor assymetry.

Perceptual and Motor Skills
2000, 91: 53-54

Blast from the Past, We’ve got our fish ancestors to thank for our love of music

By Paul Marks

Research by psychologist Neil Todd indicates that the sacculus, part of the balance-regulating system of the inner ear, may be responsible for humans’ love of music. Not only is the sacculus tuned to respond to the same frequencies as music, but the human sacculus appears to function similar to the saccular frequency of fish: “this primitive hearing mechanism from our vertebrate ancestors appears to have been conserved as a vestigial sense in humans,” according to Todd. He also believes that, because the vestibular system is closely associated with the hypothalamus (the primitive part of the brain responsible for such needs as hunger, sex and hedonistic responses), people may be receiving a pleasurable primordial buzz when listening to loud music that stimulates the balance center.

The sacculus responds only to sounds above 90 dB, but this can be easily exceeded by sounds like loud music or a person’s own voice (which can be as high as 130 dB in the larynx). Todd and colleagues Frederick Cody and Jon Banks have conducted experiments and gained saccular responses to sounds by measuring neck muscle tension (i.e., responses for head posture). Saccular sensitivity was found to range from 50-1000 Hz with peaks between 300-350 Hz.

The researchers point out that middle-C is 261 Hz, and male and female voice frequencies range up to 200 and 400 Hz respectively. Thus, large groups of people singing in choirs, chanting in churches or listening at a rock concert may be triggering extremely ancient responses that are vestiges of our evolutionary past.

(Editor’s Note: Information on the function of the sacculus as it relates to ultrasonic hearing devices can also be found in Staab et al.’s article (Feb. ‘98 HR) on “audible ultrasound” and Lenhardt’s article (March ‘98 HR) on the potential danger of ultrasonic signals.)

New Scientist
2/19/00, No. 2226: 11

Listen Up

By Neil Boyce

This article describes research being done by Ashley Harkrider at the Univ. of Tennessee in Knoxville relative to the effects of nicotine on hearing. In recent years, contradictory research about the effects of nicotine on hearing and sound processing have been published, with some studies suggesting that smoking increases auditory sensitivity and other studies indicating that it decreases the effectiveness of signal processing.

Harkrider had 20 non-smoker volunteers wear a nicotine patch and monitored their auditory brain impulses as they were listening in different types of noise. Her data indicates that nicotine may enhance the activity of neural pathways that helps the brain filter out unimportant repetitive sounds: “It may end up that the controlled use of nicotine will be beneficial in some types of hearing loss or diseases of the auditory system,” states Harkrider.

But before anyone rushes out of the office to light up a cancer-stick to better cope with adverse signal-to-noise ratios, Harkrider cautions that her study only applies to nicotine; the other nasty compounds found in cigarettes may very well be detrimental to a person’s hearing.

New Scientist
6/3/00, No. 2241: 11