Sunday, February 15, 2015

Understanding Audiograms, The Speech Banana and It's Impact of Speech

Today's blog  was reposted from Source: Leah Lefler, 2011

Understanding Hearing Loss Levels

Hearing is not an all-or-nothing proposition: the levels of hearing loss can vary immensely from person to person. The levels of hearing loss are typically defined as:
15dB-25dB Hearing Loss: This level of hearing loss applies only to children. Children who have hearing in this range are defined as having a "slight" hearing loss. These children will not need hearing aids, but should be monitored on a frequent basis to verify the hearing loss is not progressing.
25dB-40dB Hearing Loss: This is a mild hearing loss. For children, a "mild" hearing loss is not a slight difficulty: a mild hearing loss can cause major difficulties with articulation and some language acquisition skills. People with a mild hearing loss often miss the softer consonant sounds like s, t, th, and f. Hearing becomes even more difficult in the presence of background noise. Children with hearing in this range benefit from the use of hearing aids.
41dB-55dB Hearing Loss: This is a moderate hearing loss. The newborn hearing screening program is designed to pick up hearing losses in the moderate range (or greater). Individuals with hearing loss in this range will require hearing aids for conversational speech, and children will need intervention with auditory therapy to obtain age appropriate speech and language skills.
56-70dB Hearing Loss: This is a moderately severe hearing loss. Individuals with this level of hearing loss cannot hear any of the sounds of speech at typical conversational levels without hearing aids. Children will require auditory therapy and hearing aids to obtain age appropriate speech and language skills.
71-90dB Hearing Loss: This is a severe hearing loss. Hearing aids begin to lose effectiveness as the degree of hearing loss increases, due to sound distortion (caused by the amplified signal and the missing inner hair cells in the cochlea). Powerful hearing aids are beneficial to some individuals, while others will use cochlear implants to obtain access to sound. Hearing aids or cochlear implants, along with auditory rehabilitation therapy are necessary to develop age-appropriate speech and language skills in children. If an auditory-oral pathway is not selected, children can develop language through the use of sign language (such as American Sign Language, among others).
Greater than 91dB Hearing Loss: This is a profound hearing loss. Hearing aids are generally not effective for obtaining all of the sounds of speech with this level of hearing loss. Some young children will wear hearing aids to stimulate the auditory nerve until a cochlear implant is obtained. Cochlear implants are able to provide access to all of the sounds of speech, so that many children who obtain implants and have early auditory rehabilitation therapy are able to develop age-appropriate speech and language skills. If an auditory-oral pathway is not selected, children can develop language through the use of sign language (such as American Sign Language, among others).

Audiograms: Charting Hearing Ability

An audiogram: the lower frequency sounds are on the left, and the higher frequency sounds are on the right. Sound volume increases down the vertical axis
An audiogram is a graph of an individual's hearing ability.
  • The frequency, or pitch of the sound, is along the horizontal axis. Lower pitched sounds are on the left-hand side of the chart, and higher frequency sounds are along the right-hand side of the chart. A deep, bass drum would be a low frequency sound, while a shrill, chirping bird would be a high frequency sound. For the purposes of human speech, the important frequencies are from 250Hz - 8,000Hz. For reference purposes, Middle C on a piano is at 250 Hz.
  • The volume of the sound is along the vertical axis. Sound volume increases down the length of the chart. Sound is measured in decibels (dB), which does not increase in a linear fashion. 50dB is much, much louder than 10dB. 
  • The "speech banana" is the figurative area on an audiogram where individual speech sounds take place. The speech banana superimposed on the audiogram on the right is an English speech banana: each language has its own sounds of speech, and its own speech banana. Low frequency sounds like "M" and "Z" are on the left, and high frequency sounds like "F" and "S" are on the right. 


Example of an Audiogram

An example of a person's hearing loss charted on an audiogram.
This individual cannot hear the sounds highlighted in red.

The audiogram on the right is of a typical sloping moderate hearing loss. This person can hear low frequency sounds better than high frequency sounds: men would seem to have clearer voices than women or children for this individual.
This person can hear the soundsbelow the line: sounds like "J" and "B" are audible. This person cannot hear sounds above the line (highlighted in red). Sounds like "P," "CH," "F," and "S" are not audible. This person would have difficulty hearing birds chirping and vacuum cleaners, but could hear lawn mowers, dogs barking, and babies crying.
As this audiogram indicates, hearing levels can vary across the different frequency ranges. A person might have a mild hearing loss at one frequency, and a more severe hearing loss at another frequency. 

The Best Hearing Loss Simulator

Hearing loss simulations are very useful for educating parents, teachers, and friends about what a hearing loss "sounds" like. The NIOSH hearing loss simulator is extremely helpful, as it allows a person to input any audiogram and listen to what the hearing loss sounds like. The user can select a woman's voice or a man's voice to hear the difference in sound quality for a specific hearing loss. This simulator is also capable of running a simulation of hearing ability based on a person's age or for years of noise exposure (noise-induced hearing loss).

Types of Audiograms

Each person with a hearing loss has an individual hearing profile, but audiograms can be classified into general groups based on the shape:
The various types of audiograms . Source: Leah Lefler, 2011
Sloping: This is the most common audiogram. A person can hear low frequency sounds better than high frequency sounds.
Reverse-Slope: This is a rarer type of audiogram. People with conductive hearing losses often have a rising audiogram, though it is possible for sensorineural hearing losses to have a rising shape, too. In a very rare type of reverse-slope hearing loss (extreme reverse-slope), an individual may not be able to hear thunder, but can hear whispers across the room!
Cookie-Bite: This audiogram looks like someone took a bite right out of the middle of the graph. A person with this hearing loss hears low and high frequency sounds better than the mid-frequency sounds. This type of hearing loss is usually genetic, and may progress over time.
Tent-Shaped: This type of hearing loss is not very common. The individual with this type of hearing loss can hear the middle frequencies the best, but has difficulty with the high and low frequencies. Sometimes a tent shaped hearing loss develops when a person with a reverse-slope loss ages and begins to lose the high frequency sounds due to presbyacusis (age-related hearing loss).
Flat: The person with this type of hearing loss hears at about the same level across the speech frequencies. Both conductive and sensorineural hearing losses may take this shape.
Corner: When a person has a small amount of residual hearing in the low frequencies, but no recordable hearing on the rest of the audiogram, the person has a corner audiogram. A person with this type of audiogram would be a candidate for a cochlear implant.

The Flintstones Simulate Hearing Loss Levels

Other Hearing Loss and Cochlear Implant Simulations

The Effects of Noise Induced or High Frequency Hearing Loss

Hearing Loss Simulation By Frequency

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