HIS 140 - Hearing and Understanding - the Physiologic and Psychoacoustic Differences

Hearing & Understanding—the Physiologic & Psychoacoustic Differences

Decipher Code

When we travel to a country where an unfamiliar language is used, we have difficulty communicating, because we do not know how to “decipher” the language.


Decipher Code

When one attempts to hear with a damaged cochlea, the brain continues to try to decipher the “new/modified language”.


Decipher Code

As the active amplification of the cochlea begins to be reduced (dead outer hair cells), its ability to provide frequency analysis and perceive proportional loudness begin to modify the brain’s responses. (auditory deprivation)


Loudness Perception

Loudness is a perceived sensation. The ear picks up the sound and the brain interprets how loud the sound is.


Loudness Perception

We have learned that the cochlea is an amplifier. When the outer hair cells become damaged, its loudness efficiency is reduced thus, the brain receives information differently and processes loudness differently.


Loudness Perception

When we introduce loudness to the brain via amplifiers, we must understand how the damaged cochlea is modifying the loudness sensation to the brain.


Understanding

Speech is a complex frequency signal presented to the ear with multiple loudness levels by frequency. The brain processes sound information based upon the amount of time the signal has received the provided stimulation.


Understanding

The time of stimulation contributes significantly to the temporal resolution of speech information. When this time component is modified (due to damaged hair cells) the speech signal becomes less clear i.e. only limited components of the speech signal are stimulating the brain.


Understanding

As we have also learned, each ear canal has its characteristic resonant peak frequency (between 2K & 5K) which provides unique gain by frequency properties to the cochlea.

This provides perceptual loudness for each ear by frequency.


Understanding

When masking noise from whatever source is presented with the speech signal, understanding becomes much more difficult. This may be due to the reduced binaural redundancy performance of the central pathways.


Understanding & Binaural Redundancy

We learned that much auditory/sound information crosses over to the opposite hemisphere of the brain. This creates a lot of opportunities for the brain to summate sound loudness, differentiate speech from noise, and even understand speech in quiet more clearly.


Signal to Noise Ratio & Speech Understanding

This ratio shows how much stronger the desired signal is than the surrounding noise. A healthy auditory system uses its various mechanical advantages to separate the signal we wish to hear from the unwanted noise i.e. better speech understanding.


Noise & Safe Exposure

Environmental noise is the #1 cause of cochlear damage. The mechanical advantages of noise separation diminish with increasing cochlear damage. The cochlear mechanical advantages become modified when sound levels reach 85 decibels SPL.



As we learned in Zemlin earlier this week, once the cochlea begins to receive sound with greater than 85 dbSPL, the hair cells become defeated in their activity as mechanical frequency analyzers. Also, when they are exposed to longer periods of the greater sound pressure, they can become damaged.



The United States and most industrialized countries have determined that eight hours of exposure to 90dbSPL will result in permanent hearing loss. The “halving rate” for time exposure occurs with each 5dbSPL increase.



The “halving rate” simply means that the time of exposure should be cut in half with each 5dbSPL increase of sound intensity.

(Eight hours for 90dbSPL to four hours for 95dbSPL, etc)

Ref. Vonlanthen pg #240

Date post:	31-May-2015
Category:	Health & Medicine
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HIS 140 - Hearing and Understanding - the Physiologic and Psychoacoustic Differences

Health & Medicine