Binaural vs. bilateral
- In reference to the auditory system, we use the term binaural or monaural
- In reference to hearing aids themselves, we use the terms bilateral or unilateral
What are the 8 benefits of hearing with both ears?
- Reduction of the head-shadow effect
- Squelch effect
- Binaural summation
- Sound localization
- Redundancy
- Ease of listening/balancfe
- Reduced risk of late-onset auditory deprivation in unaided ear
- Tinnitus suppression
What is the head shadow effect?
- Frequency-specific decrease in SPL occurs when sound is presented to the contralateral side of the skull
- Greatest decrease occurs at the high frequencies (particularly above 1500 Hz!)
What is the squelch effect?
The ability of the auditory system to combine the information from both ears in order to distinguish speech from noise. This process is due to the CNS evaluating timing, amplitude, and spectral difference between incoming information from both sides
What is binaural summation of loudness?
Not as much power/gain needed, summation gain is approximately 3dB (can be upwards of 6 dB)
What is sound localization?
The ability to locate sound is highly dependant of perceiving sound with both ears simultaneously with slight inter-aural timing differences
What is redundancy?
The brain having essentially two chances of extracting correct information
What is the unaided ear effect?
- Auditory deprivation of an unaided ear manifests as a decrease in word recognition scores (but not necessarily change in pure tone thresholds)
- Long term unilateral hearing aid users with bilateral hearing loss can have a significant reduction in speech recognition in the ear that is not aided
- Auditory deprivation can occur over a period of years
- Speech recognition scores with aided ear stay stable, but with an unaided ear, may degrade over time
____ - can word recognition improve with amplification?
Acclimatization
- Learning-induced reorganization within the CNS can occur post hearing aid fitting (Munro, 2008)
- Hearing aids change the sensory environment by stimulating a deprived auditory system therefore, they may be capable of inducing change within the central auditory system
What are 3 reasons why people might just chose one HA?
- Financial resources
- Personal choices
- Expectations/biases prior to coming to appointment
What are 2 reasons why not to aid both ears?
- One ear is not aidable (audiological or medically)
- Audiologic: no residual hearing
- Medical: examples may be atresia, microtia, significant stenosis of the canal, significant/chronic infections - Binaural Interference
What is binaural interference?
- Seen in degraded performance of WRS
- When the performance of the poor ear degrades the performance of the better ear
What is the prevalence of binaural interference?
Between 8-10% of the elderly population
Give an example of binaural interference
- One ear is good WRS (92%)
- Other is poor (40%)
- Binaurally, the score is 70% (the poor ear is pulling down the score of the good ear)
- We do not want to degrade the performance of the better ear
Guidelines of unilateral fittings (1)
Fit the ear with the best ____ because…
WRS (gives better overall clarity)
Which ear should be aided?
Left (better WRS score)
Guidelines of unilateral fittings (2)
Fit the ear with the ____ audiometric configuration (unless…)
Flattest, the WRS is poor (but flat typically has better WRS anyway)
Which ear should be aided?
Right (flat configuration)
Guidelines of unilateral fittings (3)
Fit the ear with the widest ____
Dynamic range
Which ear should be aided?
Right ear
- If the left was fit, we would have to compress all speech information in a smaller range
Guidelines of unilateral fittings (4)
If the thresholds are ____, fit the better ear
45 dB or worse bilaterally (fit the ear with the better thresholds)
Which ear should be aided?
Right (better thresholds)
Guidelines of unilateral fittings (5)
If the better ear, ____, is able to contribute to speech intelligibility, fit the ____ ear
Unaided, poorer
Which ear should be aided?
Here, the right ear is contributing more to speech without a HA, fit the left ear as it needs more “help”
