Title: Unit 2 Lecture
Course: 14SP-HIS-150-GWB2-HEAR. INSTRU. FITTING METHODS > Section: Lessons

Unit 2 Lecture

It’s hard to believe it is already the start of the second week!  I’m sure you are already finding that the information in this course is a lot to take in each week.  It will be especially important that you log into the course several times a week and keep up with the work.  Some it of will take some time to think through and understand how you will be applying it as you begin to understand that fitting hearing instruments includes both science and art.  As you have already seen in Unit 1 you will have two attempts for the unit quiz and your best grade will be kept.  While you may use your textbooks and notes to take quizzes, you will find that keeping up with the assignments and coursework will better prepare you for the quiz.  In addition, if you are starting to master the information and don’t need your textbooks and notes you will be better prepared for the midterm and final.  Remember all the information is cumulative.  It isn’t that your instructors are trying to be difficult.  We want you to be prepared for the state exam in Missouri or any other state you choose to become a licensed hearing instrument specialist.

A few tips before we look at this week’s information:

- Make sure you have reviewed the Syllabus and put the midterm and final dates on your calendar.  You are required to complete the Syllabus review assignment in Unit 1.  The instructions for Unit one asked you to review the Syllabus first and do the review before moving on to the Unit 1 material.  I see in the grade center three people have not completed the Syllabus review yet.  If you are one of the three please make sure you get this done.
- Make sure you know where you will be taking your proctored exams, the location’s procedures and the hours it is open.  Please don’t wait until the last minute to make arrangements for your midterm and final exams.  Extensions will not be given for lack of planning ahead.
- I have been reading your discussion posts this weekend.  Well done.  Please remember that the details matter here!  In the other courses I have taught this year I saw the initial posts were good but the response posts lacked meaningful information in a lot of cases.  Response posts that say “good post” or “I didn’t think of that” are not adequate.  The response post must contain meaningful information to continue the discussion started by the author’s initial post.  Including references from your text or especially outside of your course textbooks in all of your posts will increase your discussion score.

Fitting Methods

As you read this week’s assignment in your Venema textbook and review the PP information I’m sure you will be asking “how can there be so many ways for calculating gain and compression?” and “after all this time hasn’t one formula or one method for calculating gain and compression proved through research to be the best method for providing audibility for sensorineural hearing loss?”  As you will see from the history of linear hearing aids and then moving to hearing aids that provided compression, we have learned a lot but there isn’t one perfect method.  As much as you have already learned about the cochlea there is still a lot we don’t know.  We do know that there are two components to senorineural hearing loss “loss of sensitivity” and “distortion”.  Although we can measure the loss of sensitivity we don’t have a good way of measuring the distortion component.  A lot of research was done over the years looking for the best way to provide audibility even though we know there is a lot of variation among clients and their abilities.  You will also have the experience at some point of see two different people with essentially the same audiogram and discrimination but who end up having very different experiences with amplification.  In this course we will focus on the history of how we got to where we are with fitting formulas and the two most common independent fitting rationales- NAL and DSL.  The historical background is important.  You need to understand where we came from to have an appreciation for where we are today.  I think it will also help you better understand compression in general and the types of compression used in the past and today.  Compression is one of those concepts all fitters of hearing instruments struggle with at first.  Some continue to struggle with it for a long time.  It is somewhat like masking.  At first it seems impossible to understand and then all of a sudden the light bulb goes on and it makes sense.  Think of fitting rationales and compression the same way.  At some point it will all make sense!

What is a rationale?  Or fitting method?  Think of them as formulas for calculating gain and compression.  While we are focusing on the main two independent rationales in this course you will see from manufacturer’s fitting software and at your practicum sites that many manufacturers’ have their own proprietary fitting rationale.  So why don’t they all use NAL or DSL for all their products.  While many manufacturer’s offer these rationales they have their own as well.  Your textbook talks about these a little.  Any rationale whether it is proprietary or independent is based on a philosophy.  It is up to you as the hearing care professional to learn that philosophy and how the rationale calculates gain and compression for various configurations of hearing loss.  Then it is also up to you to determine if that rationale stands up to scrutiny.  Does it follow the philosophy it said it did and how well does it provide audibility.  Unfortunately there isn’t one way of calculating gain and compression that will work for every single person you fit but we do know a lot about how to use the rationales that have been developed and can provide good audibility for a lot of clients with sensorineural hearing loss.  So why do manufacturer’s have their own fitting formula?  In the early days there were a lot of researchers in independent labs working on this idea and why kind of signal processing was best in a hearing instrument.  As hearing aid technology developed, many of these researchers were hired by the hearing aid manufacturers.  As the manufacturers added other technologies such as directional microphones and noise management they knew all these technologies and providing good audibility had to live together in the hearing instrument.   Because of this they wanted good signal processing research going on in their own facilities rather than only in independent labs.  You will find as you look at the proprietary rationales in addition to the independent ones we will review, not all are created equal.  There are good and not so good.  It will be up to you to determine how they live up to the philosophy they were created from and how well they provide audibility.

Dead regions- This is another topic you see in your reading this week.  While we know they exist and you see a way of determining dead regions (the TEN test) we are still learning what to do with this information as well.  You will find there is a lot of discussion in this area and not everyone agrees on every point.  Some more recent research indicates that dead regions can be very isolated.  A narrow frequency area rather than a broad one.  You won’t see the TEN test done on a regular basis in most clinics and other researchers are not all in agreement about its validity.  Based on this idea of dead regions and inner hair cell damage you will read about some people with SNHL not being able to make use of amplified sound.  Again you will see a lot of variation in the discussions of this concept.  You will start to learn there are various opinions about how much high frequency amplification should be given and other considerations for gain and compression.

The two rationales we will focus on in this unit are NAL and DSL.  NAL is the one you will become most familiar with as hearing instrument specialists because you will be fitting adults.  DSL was originally created for the needs of children.  While there is an adult version, most hearing care professionals don’t use it.  NAL is by far the most popular fitting method of the two for adults.  They are based on two very different philosophies and have significant differences in their gain and compression calculations.  Both have gone through several revisions.  In this unit we will focus on the background of the two philosophies and how they have developed.  I will add more information later about the current version of each one.

Have a great week of learning!  Remember you can post questions for the class or for me in the discussion board.  This week I will be attending the American Academy of Audiology convention in Orlando Florida.  I know it’s terrible to have to go to Florida.  I will be able to check e-mail and Blackboard most days except Thursday and Friday.  I will do my best to log in those days even if it is only for a few minutes to check messages.

Dr. Senay

Attached Files: | - HIS 150 Unit 2 Lecture.docx