Binaural Hearing Impairment
Frequencies Used
5, 1000, 2000, 3000
why it is important to mask correctly (5)
1. rules out NTE participation
2. ensures the TE responds
3. masking errors lead to inaccurate results, incorrect tx, and poor outcomes
4. physicians make decisions on ear surgery based on audio results
5. recommendations about management are based on results
when to mask for supra-threshold speech testing
PL te - best BC NTE @ 500, 1000, 2000 is greater than or equal to IA
undermasking
insufficient masking to effectively mask in NTE
IA
reduction in sound energy as it is transmitted between ears
low fence information
25 dB HL, starting point for compensable HL, below this is 0% binaural impairment
crossover
perception of sound in one ear that has crossed over the head via BC transmission of a sound presented through an earphone to the opposite ear
how much to mask for supra-threshold speech (simplified and non-simplified)
simple: dB EM: PL te - 20 dB ONLY IF no ABG and if speech is presented at moderate SL (30-40 dB SL re:SRT)
regular: PL te - 25 + avg. ABG NTE @ 500, 1000, 2000
plateau
pt's response level remain the same, as masking level is increased, and this is the masked threshold
IA levels for supra-aural, inserts, and bone
40, 60, 0
high fence information
92 dB HL, level at which binaural impairment is 100%
when to mask for AC
AC threshold TE - best BC NTE is greater than or equal to IA
or
AC thresholds of TE - AC thresholds of NTE is greater than or equal to IA
when to mask for SRT
- SRT te - IA is greater than or equal to BC NTE @ 500, 1000, 2000
- SRT te - best BC NTE @ 500, 1000, 2000 is greater than or equal to IA
- SRT te - SRT NTE is greater than or equal to IA
- if NTE has AC and BC thresholds that differ, compare SRT in te to best BC in NTE
overmasking
masking level so intense that noise crosses over and is heard in TE (masking level of NTE exceeds IA)
crosshearing
when NTE hears stimulus presented to TE (if stimulus level to TE equals or exceeds IA)
Better ear and worse ear weighting
5:1, weights importance of HL in better ear vs. poorer ear
better ear is the lower number
initial masking level for AC testing
AC threshold of NTE + SF + CF
SF = 10 or 15 dB
CF on audiometer
when to start masking for SRT
PL te - 35 dB + avg. ABG NTE
masking is needed for BC
ABG 15 dB or greater
Occlusion Effect
a low frequency BC phenomenon, improvement in LF BC thresholds when ear is occluded since intensity received at cochlea is increased due to inability of LF energy to escape out of ear canal
How to calculate
1. calculate 4 frequency average in each ear
2. determine percent of monaural impairment in each ear (PTA-25) * 1.5
3. calculate percent of binaural impairment 5 (better ear impairment) + (worse ear impairment) /6
initial masking level for BC testing
AC threshold NTE + SF + CF + OE
OE = 20 at 250, 15 at 500, 5 at 1000
use plateau method
SF is 10-15 dB
CF if necessary
when is a masking dilemma most likely
-significant ABG is present in NTE
---if NTE has ABG, initial masker level will exceed max permissible masking
-bilateral CHL or significant bilateral MHL
masking steps
5 or 10 dB
central masking effect
elevation in hearing sensitivity of TE, on the order of 5 dB, as a result of introducing masking noise into NTE due to influence of masking noise in central auditory function and may occur during AC, BC, or speech testing