Exam 1 Part 1 Flashcards
Describe how frequency resolution changes with SNHL. Why does reduced frequency resolution make it difficult to understand speech in noise?
Auditory filters (critical bandwidth) must be intact to efficiently process complex signals the cochlea needs
The cochlea analyzes signals using a bank of overlapping band-pass filters
These filters allow regions of the cochlea to “pay attention” to a specific frequency region while ignoring frequencies outside of the band
In normal hearing, sharp tuning curves allow for precise frequency discrimination & perception of sounds
w/ HL, the curve is broader and noise can easily affect perception of the desired signal
Noise energy peaks around 250 Hz but upward spread of masking impacts audibility up to about 1500 Hz
can amplification fix frequency resolution changes?
no
PT will face this problem and make them aware of this - do not give the impression that premium amp can make it all better
If you do not have a sharp tuning curve, the signal gets masked making it difficult to hear in noise
Define temporal resolution and the auditory processes which support it.
The ability of the auditory system to detect time related changes in the acoustic stimuli over time
Needed in order to understand speech in noise
Time related Cues
Phonemic duration - can vs cant
Gap detection - soon vs spoon
Can we hear the small brief pauses between words, syllables etc.
Temporal ordering (boots; boost)
Suprasegmentals
Provides us with meaning (is it a question, a demand, etc.)
If there is a temporal resolution hearing problem, can a standard hearing aid fix this? What is a non amplification method to improve understanding with temporal issues
It will not fix it
Talk slower, enunciate
Just as effective as amplification can be
If we cannot hear and distinguish timing differences, makes it hard to untangle speech in the sea of noise and makes the issue PT have with hearing in noise more prevalent
what cues allow us to localize where sound is coming from
ILD
ITD
Describe the benefits spatial hearing supplies
Spatial hearing allows us to
Determine location of a sound source
Unmask sounds otherwise masked by noise
Brain combines and analyzes info arriving from both ears for improved signal detection & identification of speech in noise
Shift our attention and focus on one sound source while ignoring another
Feel connected with the environment
what is spatial hearing
Localizing where sound is coming from by using ILD & ITD between ears
Explain binaural loudness summation. Its suprathreshold benefits and how this benefit supports hearing aid fitting strategies.
Results in PT perceiving greater loudness w/ bilateral devices
Less gain is needed to reach comfortable listening levels
Can fit a PT with less loudness in order for them to hear the words
@ threshold increase only around 2-3dB
@ suprathreshold increase around 6-8dB
Explain binaural squelch and the benefit this auditory process supplies
ability of the auditory system to combine the information from both ears centrally and segregate the speech from the noise by the differences in sound between both ears.
Leads to improved intelligibility in noise & ability to focus on 1 signal while ignoring others by taking advantage of these differing SNRs
Which frequencies supply the most information on interaural level differences?
High frequencies (>3 kHz) to identify ear to ear head shadow level differences
Which size receiver maximizes HF output
Small - because the aperture is able to move faster and quicker
HF signals need rapid diaphragm movements
This is done w/ smaller receiver because it makes the diaphragm smaller and stiffer
Severe HL that needs high frequency output
Dual receiver - gives benefit of both & has a big receiver so you need a custom receiver (embedded) or a larger BTE that has the larger receiver
2 receiver system that sums both receivers before reaching the ™ where one is optimized for LF and the other HF which reduces battery drain, gives a good EHF output w/out compromising a lot in LF and minimizes saturation distortion potential
Difference bw WDRC & FDRC
Initial TK is lower (10-15) in FD than in WD
Which needs lower tk?
Consonants - HF, less energy, softer
expansion
needed when someone complains about some of soft sounds they do not need to hear are too loud
Lower output with very very soft sounds
0-20 dB input
Really low CR (lower than linear; <.9:1);
WDRC
needed to get soft sounds louder & expand dynamic rang
manages incoming signals
Input compression (AGC-i: amp electric signal comes in & will )
-Engages BEFORE volume control
-activates at the pre-amplifier when TK is low input level & signal is louder than this (bw 20-50)
LOW tk
LOW CR - 1.1:1-4:1 (almost linear)
Slow AT & RT
-Slower AT = temporal fine structure preserved in speech signal
-Slower RT = reduces times of inaudibility to very soft consonant sounds after compressor releases
temporal fine structure preserved in speech signal
Slower AT
reduces times of inaudibility to very soft consonant sounds after compressor releases
slower RT
OLC
Output compression (AGC-o)
-LOUD SOUNDS
need this to protect the ear
Engages AFTER VC
Hight TK: >/= 80dB SPL
High CR: >/= 5:1
Attack time is fast to protect ear from loud sounds
-Release time is variable
-Sudden noises = fast
-Sustained loud noises = slow
Differentiate those services Medicare will and will not reimburse
No
Anything that relates to HA’s
Yes
Anything medically necessary
what are 3 methods used to reduce external feedback
Adaptive Digital Feedback Suppression (DFS)
reduce external loop
digital notch filtering
digital feedback cancellation
Describe 3 methods used to reduce external feedback
Reduce external feedback loop
Increase snugness of mold to reduce size of slit leaks
Or decrease vent size to stop feedback path
Limitation: both increases OE
Digital notch filtering
Removes frequencies around the noise - reduces gain around 2-4 kHz where feedback occurs
HA between this range with notch creates a notch in frequency response so we don’t amplify sound in those regions -
reduction in gain from 2-4 kHz and if you don’t turn the volume up it won’t cause feedback
Limitation 35% of intelligibility comes from this range alone so you stop feedback but stopped audibility of important speech sounds so reduced speech intelligibility
Digital feedback cancellation
When HA detects feedback (identified due to steady state noise bw 2-4 kHz) an algorithm creates an out of phase clone of the signal (duplicate of the feedback) and this causes the clone to be subtracted from the amp path and in turn attenuates the feedback
what is the purpose of frequency lowering
tries to improve HF audibility by shifting it down to LF
used with someone that has residual hearing and loss in HF makes it impossible to reach hf amplification (cannot get them to ever hear these sounds again)
Frequency lowering: describe the 3 types, their uses and limitations
Linear Frequency Transposition
Improves HF audibility by moving HF band one octave down to LF region
CUT AND PASTE into LF, takes the highs and shoves it into the lows
Nonlinear Frequency Compression
HF range is compressed into a LF range; squishes it down into the audible region
maintain tonotopic order more, lowered all the frequencies, squished into lower frequency space, close to each frequencies close to their original spot
Spectral Envelope Warping
Leave the HF where it is but also COPY and PASTE into LF
