Download Self assessment for using the Hearing Aid Selection (HAS) stack to

Self assessment for using the Hearing Aid Selection (HAS) stack to assist with
judgments in hearing aid fitting.
Go through the following steps. At each step document very carefully what you have
done, so that another person could replicate your findings. You lose points if I
cannot verify your results. You can document your work in whatever way is most
efficient: writing it down, printing an HAS card, printing from the Fonix 6500, etc.
Begin with HAS in its default state (normal hearing, speech at ACL, normal REUG,
vents closed, etc.).
1. You need to begin with a hearing loss. Also, write a brief history for your patient.
Choose a typical sensorineural hearing loss and enter it into HAS.
Questions:
•Are you testing with supra-aural headphones or insert earphones?
•What is the REDD? Change the REDD for a couple of frequencies and
observe/document the effect on the audiogram. When you are finished, reset the
REDD to normal.
•What is the effect, in percent correct for words and sentences, of this hearing loss
on the patient's ability to hear ACL speech? Speech that is faint (55 dB SPL)?
•Does this patient need a hearing aid?
2. Determine real-ear targets for gain and output.
Questions:
•What procedure did you use for selecting a target gain curve? What effect does this
have on improving speech intelligibility? Your answer should be in percent correct.
What is your target REIG?
•What method did you use to estimate the LDL? What values did you obtain for
LDL? What is the RESR?
3. Convert the real-ear targets to 2-cc coupler targets. You need to select a type of
hearing aid (i.e., BTE, ITE, ITC, etc.).
Questions:
•What is the target 2-cc coupler use-gain and FOG? Use 15 dB of reserve gain for a
BTE, otherwise use 10 dB.
•Is the coupler use-gain greater or less than the REIG? What are the four major
reasons why real-ear gain is different from coupler gain?
•What happens to the target REIG as you change the type of hearing aid? What
happens to the 2-cc coupler gain as you change the type of hearing aid. Document
what the effect is from changing from an ITE to a CIC. Why is there a difference?
•What is the target OSPL90? Does this change with type of hearing aid? What is the
change?
•Do you want the target OSPL90 to equal the OSPL90 predicted from the LDLs? Or,
do you want the OSPL90 to be less? If so, how much less, and why?
4. Measure the REUG; enter it into HAS to customize your targets. You can use the
Fonix 6500 to measure an REUG, either your own or a friend's.
Questions:
•How does the measured REUG differ from average?
•Does changing REUG change the target REIG? Does it change the target 2-cc
coupler use gain or FOG? What is the difference?
5. Measure the RECD; enter it into HAS to customize your targets again. You can
use the Fonix 6500 to measure an RECD, either your own or a friend's.
Questions:
•How does the measured RECD differ from average?
•Does changing RECD change the target REIG? Does it change the target 2-cc
coupler use-gain or FOG? What is the difference?
•How does changing the RECD affect the relationship between RESR and OSPL90?
6. Select a hearing aid for the purpose of matching the target 2-cc use-gain and
OSPL90. Adjust the VCW and trim pots until you obtain a reasonable approximation
to the targets.
Questions:
•How close were you able to come to the target 2-cc use-gain and OSPL90 curves?
•Compare the peak use-gain with the peak FOG to determine the reserve gain.
What was the reserve gain?
7. Determine the REIG and RESR of the hearing aid. Keep the hearing aid VCW in
the use-gain position you selected to match the coupler target. You can measure the
hearing aid in your own ear, or you can recruit a friend. Use a custom earmold. If
you don't have a custom earmold, try an alternative: a Comply earmold, Doc's
Promold, or you can fabricate one from a silicone ear impression (or use Insta-Mold).
Questions:
•How closely did your predicted REIG and RESR match you measured REIG and
RESR?
•Were you able to modify the hearing aid/earmold to achieve a closer match? How
closely were you able to come to matching the target REIG and RESR?
8. Compression. Use HAS to determine target compression ratios and input-output
functions.
Questions:
•Select the "Compression" menu item from the "Other…" menu to observe calculated
compression ratios. Describe the logic behind how these compression ratios were
calculated.
•Select the "Input-Output Function" menu item from the "Other…" menu. Use the
capabilities of this card to match the target input-output function for a frequency.
How was the target you are trying to match obtained? Assume that you are trying to
match the target in the test box. What settings did you choose for the compression
amplifiers?
•Place the hearing aid in the test box and run an input-output function. Compare
your measured input-output function with the ideal input-output function. Its likely
that there are differences. How will these differences affect the patient's perception
of loudness at different input levels?
9. Earmold venting. Use HAS to predict the effects of venting. Select different vent
lengths and diameters.
Questions:
•How do the venting changes affect the REIG? The 2-cc coupler use-gain?
•Choose one particular vent and describe how (compared to the closed mold) the
vent affects the audibility of the speech spectrum. What is the difference in
intelligibility between the vented vs. unvented condition.
10. Special earmolds. Use HAS to predict the effects of earmold modification.
Select different earmolds and observe the effect of each on the REIG and RESR.
Questions:
•Choose an earmold that will increase the high frequency response for the listener.
What is the effect upon the REIG and RESR? The 2-cc use-gain?
•Identify an earmold that might help with reducing feedback. Hint: Feedback is
related to high frequency gain.