Each child who is deaf or hard of hearing is unique in what they can and cannot hear, and what they may or may not understand. It is therefore important to be aware of some basic information about the technical aspects of the hearing process to guide understanding of a child’s hearing abilities as they relate to spoken language and communication development. This includes understanding a) the various components of a typically functioning ear, b) what to take into consideration when the hearing mechanism is not functioning, c) the implications of varying levels and patterns of hearing, and d) other associated factors which impact a child’s hearing abilities.
The process of hearing depends on sound being transmitted through the ear to the brain. To understand the hearing abilities of a child who is deaf or hard of hearing, it is first helpful to understand the four major components of the hearing mechanism and their purpose.
- Outer Ear: The outside of the ear, plus the ear canal up to the eardrum or tympanic membrane.
- Middle Ear: The cavity behind the tympanic membrane which houses three small bones that help conduct sound waves to the inner ear.
- Inner Ear: The cavity behind the middle ear which houses a series of channels known as the labyrinth, and a snail-shaped structure called the cochlea. The labyrinth is integral to the human balance system. The cochlea contains the thousands of hair cells responsible for sensing sound and transmitting it to the brain for processing.
- Auditory Nerve (8th): The eighth cranial nerve, which is the pathway of sound from the ear to the brain.
Implications: When the hearing mechanism is not functioning
Hearing may be impacted in various ways depending on which component(s) of the hearing mechanism are not functioning. Below is a description of what occurs when there is an interruption to sound transmission as it travels through the ear to the brain; and what this may indicate for a child who is deaf or hard of hearing.
A. Outer and/or Middle Ear: When there is an interruption to sound as it moves through the outer and/or middle ear to the inner ear and auditory (8th) nerve, this is referred to as a "conductive hearing loss." Common causes are excess wax in the outer ear, or fluid behind the eardrum in the middle ear. Many circumstances are temporary and can be resolved with medical treatment. Some children, however, may have long-term or permanent conditions which are more difficult to remedy, such as malformations of the outer and/or middle ear.
Implications: When there is a "conductive hearing loss," this typically causes sound to be muffled or quiet. Moving closer to, or increasing the loudness of, the sound source may be helpful in improving the ability to hear and understand. The duration and nature of a conductive loss will influence a student's hearing ability. If the condition is brief and not frequently recurring, it should not affect language or academic development. If the blockage is chronic or repeated, it may negatively influence speech, language, and educational performance and require intervention strategies. Use of a hearing aid or other assistive listening device may help some students experiencing a long-term "conductive hearing loss."
B. Inner Ear/Eighth Nerve: When the hair cells in the cochlea, responsible for sensing the pitches of sound, and/or the auditory (8th) nerve, responsible for conveying sound to the brain, are non-existent, malformed, or not functioning, this is referred to as a "sensorineural hearing loss." The outer and middle ears are functioning. There are many different causes of "sensorineural hearing loss," some developing before or during birth, and others having a later onset. These conditions are usually permanent and typically cannot be remediated through medical interventions. One category of a neural loss is referred to as Auditory Neuropathy Spectrum Disorder (ANSD). This condition is related to a breakdown in transmission of sound from the inner ear to the brain. Students with ANSD may be aware of sounds, but experience challenges in decoding and understanding what they hear. For more information about ANSD, see NIDCD's page.
Implications: The nature and extent to which the hair cells in the cochlea and/or the auditory (8th) nerve are impacted, will influence a student's ability to hear and understand spoken language. In addition to causing listening challenges related to the loudness of sound, these conditions may also cause distortion in the hearing system. Each student is unique in how they may benefit from amplification (e.g. hearing aid, cochlear implant, or other assistive listening device) to understand spoken language, and the language and communication approaches appropriate for each child.
C. Mixed: A combination of both a conductive and a sensorineural loss.
Implications: The overlap of a conductive and a sensorineural loss presents a cumulative listening challenge related to the extent of each condition. The sensorineural component typically remains stable, however, depending on the cause of the conductive component (i.e. fluid in the ear, excess wax), a child may experience a fluctuation in hearing levels. When hearing levels fluctuate, it can impact day-to-day listening and attending as well as the effectiveness of a hearing aid(s).
D. Unilateral: Typical hearing in one ear and reduced hearing in the other ear.
Implications: The experience of each child with unilateral hearing is unique. They may face varying levels of social, academic, or behavioral challenges related to locating the source of a sound, listening with background noise or at a distance, or attending in the classroom. A child may or may not need special accommodations in the classroom, such as preferential seating for maximum accessibility to auditory information or use of a sound-field FM system. Individuals with unilateral hearing should be monitored closely for linguistic, educational, or social gaps. For more information about unilateral hearing see: http://www.asha.org/public/hearing/Unilateral-Hearing-Loss-in-Children/.
Implications: Varying levels and patterns of hearing
It is next important to understand the implications of an individual's hearing levels related to their ability to use their listening to understand spoken language. While some children who are deaf do in fact have no residual (remaining) hearing, most children have some degree of measureable hearing. Hearing levels are documented on a graph called an audiogram. The audiogram charts the intensity (loudness level) at which a student is aware of various frequencies (pitches) of sound.
Some of the terms used when describing hearing levels include:
- Hertz (Hz): The frequency or pitch of sound.
- Decibel (dB) - The terminology used to describe the intensity or loudness of a sound. Zero dB is usually the quietest sound measured on an audiogram. The loudest sound typically measured is 120 dB.
- "O" and "X" - The symbols used to record thresholds on an audiogram. "O" represents the right ear and "X" represents the left ear.
- Pure Tone Average (PTA) - The average of the thresholds at 500 Hz, 1,000 Hz, and 2,000 Hz for each ear. The PTA is often used to describe an individual's degree of hearing loss (see below). For example, when a hearing loss is described as an 80 dB loss, that number probably represents the PTA. Hearing should not be described in percentages.
The hearing levels typically described within an audiological report are as follows:
Hearing within normal limits: 0 to 15 dB
Slight: 16 to 25 dB
Mild: 26 to 40 dB
Moderate: 41 to 55 dB
Moderately severe: 56 to 70 dB
Severe: 71 to 90 dB
Profound: 91dB +
Based on the American Speech-Language and Hearing Association: http://www.asha.org/public/hearing/Degree-of-Hearing-Loss/
Patterns (Configurations) of Hearing
During an audiological evaluation, an individual's hearing levels are charted on an audiogram from the low frequencies (250 Hz) through the high frequencies (8,000 Hz). Speech sounds have energy in different parts of the frequency range. For example, vowels have most of their energy in the low frequencies, while many consonants have energy in the higher frequencies.
Speech understanding is related to how many parts of the listening "puzzle" are available for someone to make sense of words, phrases, or sentences. The more parts that a person can hear, the easier it is to understand what is heard. Some sounds are more important than others for speech understanding. In general, consonants provide more information and are therefore more important for speech understanding than vowels. For example, "SP_C__L" is easier to understand than "__E_IA_."
When looking at an audiogram, some typical patterns of hearing emerge that have the following impact on an individual's ability to understand speech.
- Flat: Can hear both the low and high pitches at the same level. With a flat pattern, a student is aware of most speech sounds which makes it is easier to understand speech than when a student cannot hear all of the pitches.
- Sloping: Can hear more in the low pitches than in the high pitches. An individual may miss many of the consonant sounds critical to understanding speech. For example, a student may miss sounds such as "s" and "d" which are important to distinguishing plural and past tense.
- U-shaped (or cookie bite): Can hear more in the low and high pitches, than in the middle pitches. With this pattern, individuals can often fill in the gaps and understand spoken language, because they hear both the high- and the low-pitched speech sounds.
- Rising: Can hear more in the higher pitches than the lower pitches. This provides an individual with many of the consonant sounds beneficial to speech understanding. Even without fully hearing the low-pitched vowels, access to most consonants facilitates the ability to understand spoken language.
Other Associated Factors
It is important to keep in mind that there is no single description or profile of "deaf" or "hard of hearing" that fits all. An individual's ability to understand spoken language is influenced by many factors in addition to hearing levels and patterns of hearing. Even if two individuals have the same audiogram, it does not mean they will hear and understand in the same way.
Some of these factors include:
- Age when an individual first became deaf or hard of hearing
- Age when an individual was first identified as deaf or hard of hearing
- Age when hearing aids were first fitted
- Level of benefit obtained from a hearing aid for understanding spoken language
- Level of benefit from a cochlear implant (for children who are candidates)
- Consistency of amplification use (hearing aid, cochlear implant, FM system)
- Educational and communication approaches used
- Quality of auditory, speech, and spoken language habilitation
- Valuing and use of spoken language in the child's environment
For more information about hearing aids, see: Info to Go/Hearing Aids
For more information about cochlear implants, see: Info to Go/Cochlear Implants
For additional resources about hearing, see:
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