Hearing Aids: Standards, Options, and Limitations
RATING: (5 of 5 ears) for students;
(3 of 5 ears) for established audiologists
EDITOR: Michael Valente
PUBLISHER: Thieme, New York
REVIEWER: Melanie Herzfeld, Au.D., ProHealth, Lake Success, New York
SYNOPSIS: Dr. Valente has gathered well known experts in the field of amplification to provide explanations of diverse subject matter pertaining to hearing aids in this second edition. Changes from the first edition are rampant; three chapters have new authors and four chapters have been exchanged. The nine chapters include information on probe microphone measurements, detailed information on telecoils, microphones and receivers, amplifiers and circuit algorithms, adjustments to hearing aids, information on nonlinear hearing aids, speech in noise improvement strategies, a chapter on research in digital processing, and auditory rehabilitation. The information is to the point and timely and still includes direction for future concerns.
REVIEW: In the first edition of this book, Chapter One was concerned with standards groups and while certainly interesting and important, the change to a more practical chapter was a definite plus. This new chapter by George Frye is a good introduction to the book, enticing the reader to continue, rather than a stand-alone chapter.
In order for an audiologist to competently address the needs of the hearing impaired population, understanding the microphone, telecoil, and receiver is vital. Chapter Two written by Stephen Thompson provides basic information on microphone performance, directionality, and limitations. Similar treatment is given to telecoils and receivers. This chapter seems to be a good starting point to learning about these important components.
Dr. Jeremy Agnew presents two chapters; he starts in Chapter Three by providing a quick overview of amplifiers and circuit algorithms, touching briefly on the different classes of amplifiers and introducing a neat flow chart of the digital hearing aid fitting process. In Chapter Four, adjustments are explained, again in a brief manner. From this chapter, one can be introduced to the concepts of filtering, various limiting options, potentiometers and remote controls, and end the chapter hopefully wishing for more information.
For those audiologists who do not understand compression, Dr. Francis Kuk explains compression kneepoints and ratios in a clear and concise manner. He offers explanations of attack and release times, the impact of various noise reduction algorithms, the differences between the various types of devices, and the impact that each change has on the verification and validation procedure. In an era when documentation is so critical, the importance of verification and validation is a timely concern and one that must be addressed by each audiologist.
Once one has a hearing aid, the plumbing becomes critical and Chapter Six written by Dr. Michael Valente, Maureen Valente, Jane Enrietto, and Karen Layton, presents information on "Earhooks, Tubing, Earmolds and Shells". Here one can read about the benefits of silicon impression materials, the characteristics of Libby Horn tubing, the effect of venting on gain as well as find a troubleshooting guide to hearing aid/ear mold problems, to name just a few.
Directional mics have been shown to provide a nice speech to noise advantage and Dr. Todd Ricketts and Andrew Dittberner present information on directivity, directional patterns and their calculations along with problems impacting directivity. The formulas actually enhance the presentation, although few will actually run the calculations.
"Review of Research on Digital Signal Processing", written by Drs. Craig Newman and Sharon Sandridge, provides a quick overview of how an evidence-based approach can be used to justify a hearing aid decision. A review of the literature is presented and findings are reported that compare analog and DSP circuits as they existed between 1998 and 2001. These findings show that while both types of hearing aids provide improvement in audibility and speech recognition in noise, the only clear advantage of DSP over analog was in the judgment of the users. It is made clear that while differences may actually be greater than what is now demonstrated, the tools to identify the advantages might still not be available.
Drs. Carl Crandall and Joseph Smaldino, along with M. Samantha Lewis and Brian Kreisman present Chapter Nine, "Auditory Rehabilitation Technology: Improving Communication for Individuals with Hearing Loss". This chapter addresses room noise and reverberation, use of assistive devices and communicative repair strategies. Hearing aids alone are not the answer and these pages include a brief overview of many necessary assistive devices that should be understood by every audiologist as well as a short checklist of ways to reduce room noise and reverberation.
CRITIQUE: Having recently reread the first edition of this book, I actually was looking forward to finding out if the new edition met all my criticisms of what now needed to be included. I am pleased to say it did and that the new edition is more enjoyable and, of course, timely.
Clearly, the intended audience for this introductory book is the graduate student taking his or her first or perhaps second course in amplification. For that audience the book is a must. For those audiologists whose training was long ago and who have not yet ventured back into the academic world or for those who feel intimidated by hearing aids and their peripherals, this book serves a definite purpose on their bookshelves. It is a well written, easily read introductory book.
For those in the field who understand hearing aids, reading this might serve to fill in some gaps. Just to see how to use probe mic systems to check a CROS hearing aid might be a valuable asset. Or perhaps one might benefit from knowing a bit more about FM systems for those who do not handle FMs regularly. Perhaps for this group, it is a great book to have in the library.