Background: Automatic DSP (digital signal processing) features, widely available in hearing aids
today, are useful because they alleviate the need for the hearing aid wearer to manually
adjust the hearing aid as listening conditions change. Although the theoretical basis
for the design of these features may be sound, little is known about their behavior
in the real world. Data logging offers a glimpse into the life of the individual hearing
aid wearer, but there are no published data to date that provide a frame of reference
for the interpretation of this information. Further, data logging in hearing aids
provides only aggregate summaries for individual features, ignoring complex interactions
including the differences between the left and right sides of a bilateral pair.
Purpose: The purpose of this study was to determine the typical behavior of three automatic
DSP hearing aid features—expansion, directionality, and noise management—in daily
life.
Data Collection and Analysis: Ten individuals with hearing impairment were fitted bilaterally with BTE (behind
the ear) hearing aids. The hearing aids were programmed for the individual's hearing
loss with expansion, directionality, and noise management set to activate automatically.
A PDA (personal digital assistant) logged the input level and status of expansion,
directionality, and noise management from both devices at 5 sec intervals. Data were
gathered in this manner over a period of 4–5 wk.
Results: A total of 741 hr of hearing aid use were logged, 50% of which were spent in environments
no louder than 50 dB SPL. Expansion, directionality, and noise management were active
45, 10, and 21% of the time, respectively; the median amount of gain reduction for
noise management was ˜1 dB. Although expansion and noise management were always active
at the low and high input levels, respectively, activation of directionality never
exceeded 50%. Expansion and noise management were sometimes active simultaneously,
as were directionality and noise management. Bilateral agreement in feature activation
typically exceeded 80%, except when the input level was at the cusp of a threshold
for activation of a specific feature and at high input levels.
Key Words
Bilateral agreement - data logging - digital noise reduction - directionality - expansion
- hearing aids - noise management
