Auditory Impairment and Assistive Hearing, 1st Ed.

By Omnigraphics

15 percent of American adults live with some form of auditory impairment and 2 to 3 of every 1 thousand infants born in the U.S. has a detectable level of auditory impairment. This book provides information about auditory impairments and treatment and assistive-technology options, along with resources and information about living with an auditory impairment.

• Language: English
• Publisher: Omnigraphics
• Release date: Nov 1, 2020
• ISBN: 9780780818255

Book preview

Preface

ABOUT THIS BOOK

An auditory impairment may be caused by various physical conditions (e.g., childhood illnesses, pregnancy-related illnesses, injury, heredity, age, excessive or prolonged exposure to noise), and result in varying degrees of hearing loss. Generally, auditory impairments are categorized as mild, moderate, severe, or profound. An individual with a moderate hearing impairment may be able to hear the sound, but have difficulty distinguishing specific speech patterns in a conversation. Individuals with a profound hearing impairment may not be able to hear sounds at all. An estimated 48 million Americans older than 12 years had hearing loss in at least one ear. The National Health Interview Survey (NHIS) found that in 2014, an estimated 21.0 percent of adults aged ≥18 years had difficulty following a conversation amid background noise, 11.2 percent had ringing in the ears (tinnitus), and 5.9 percent had sensitivity to everyday sounds.

Auditory Impairment and Assistive Hearing Sourcebook, First Edition begins with an overview of auditory impairment and explains how auditory problems impact people. It discusses the types of impairment and related disorders and explains about the auditory impairment caused by genetics and infections in detail. It also provides information on diagnosis, intervention, and treatment for people with auditory impairment. Information about assistive hearing and disability rights for people with auditory impairment is provided. The book concludes with a directory of resources for further help and information.

HOW TO USE THIS BOOK

This book is divided into parts and chapters. Parts focus on broad areas of interest. Chapters are devoted to single topics within a part.

Part 1: Introduction to Auditory Impairment describes the basics of auditory system, its types along with information on auditory loss in infants, children, and older adults. It also discusses about communication disorders and the impact of auditory loss on the quality of life.

Part 2: Impact of Noise on Hearing Loss discusses the impact of noises in auditory impairment. This part gives information on various types of noises such as occupational noise exposure, timber, and chemicals responsible for hearing loss along with a brief note on noise exposure limits and its effects on reproductive health.

Part 3: Auditory Impairment: Diseases and Related Disorders gives information on infections responsible for hearing loss along with other factors that affect hearing such as hearing loss due to certain childhood cancers, balance disorders, age-related hearing loss, otosclerosis, and Ménière disease.

Part 4: Auditory Impairment Caused by Genetics explains the autosomal recessive and dominant nonsyndromic auditory impairment, autosomal dominant and recessive syndromic auditory impairment along with maternally inherited diabetes mellitus.

Part 5: Diagnosis, Prevention, and Treatment for Auditory Impairment is about the screening and auditory tests such as newborn hearing screening, balance tests and the instruments used in measuring hearing loss, their preventive measures along with intervention and treatment options such as medical and surgical solutions, gene therapy, and steroid injection for sudden deafness.

Part 6: Assistive Hearing for People with Auditory Impairment lists rehabilitative and assistive technology aids that can help people with auditory impairment in their daily life.

Part 7: Disability Rights for Auditory Impairment provides information about disability discrimination and disability rights for employment, public places accommodations, communication, and education. It also talks about service animals, filing complaints, and testing accommodations.

Part 8: Additional Resources includes a directory of resources that can provide help and support for people with auditory impairment.

BIBLIOGRAPHIC NOTE

This volume contains documents and excerpts from publications issued by the following U.S. government agencies: Administration for Community Living (ACL); Centers for Disease Control and Prevention (CDC); Early Childhood Learning and Knowledge Center (ECLKC); Federal Communications Commission (FCC); Genetics Home Reference (GHR); National Cancer Institute (NCI); National Institute of Neurological Disorders and Stroke (NINDS); National Institute on Aging (NIA); National Institute on Deafness and Other Communication Disorders (NIDCD); National Institutes of Health (NIH); Occupational Safety and Health Administration (OSHA); U.S. Department of Health and Human Services (HHS); U.S. Department of Justice (DOJ); U.S. Equal Employment Opportunity Commission (EEOC); and U.S. Food and Drug Administration (FDA).

MEDICAL REVIEW

Omnigraphics contracts with a team of qualified, senior medical professionals who serve as medical consultants for the Disability Series. As necessary, medical consultants review reprinted material for currency and accuracy. Citations including the phrase Reviewed (month, year) indicate material reviewed by this team. Medical consultation services are provided to the Disability Series editors by:

Dr. Vijayalakshmi, MBBS, DGO, MD

Dr. Senthil Selvan, MBBS, DCH, MD

Dr. K. Sivanandham, MBBS, DCH, MS (Research), PhD

ABOUT THE DISABILITY SERIES

At the request of librarians serving the one in four Americans who live with a disability and those seeking the information needed to understand, navigate, and manage a disability, the Disability Series was developed as a specially focused set of volumes within ­Omnigraphics’ Health Reference Series. Each volume deals comprehensively with a topic selected according to the needs and interests of these patrons. The volumes provide the authoritative health information that librarians rely on to arm consumers with the facts they need to take control of their well-being and address and inform themselves about health challenges that they or a family member or loved one are facing. Patrons seeking this information will find answers to their questions in the Disability Series. The Series, however, is not intended to serve as a tool for diagnosing disability, in prescribing treatments, or as a substitute for the healthcare provider–patient relationship. All people concerned about medical symptoms or the possibility of disability or illness are encouraged to seek professional care from an appropriate healthcare provider.

An accessible Disability Resource Center portal will serve as a companion product for this series.

If there is a topic you would like to see addressed in a future volume of the Disability Series, please write to:

Managing Editor

Disability Series

Omnigraphics

615 Griswold St., Ste. 520

Detroit, MI 48226

A NOTE ABOUT SPELLING AND STYLE

Disability Series editors use Stedman’s Medical Dictionary as an authority for questions related to the spelling of medical terms and The Chicago Manual of Style for questions related to grammatical structures, punctuation, and other editorial concerns. Consistent adherence is not always possible, however, because the individual volumes within the Series include many documents from a wide variety of different producers, and the editor’s primary goal is to present material from each source as accurately as possible. This sometimes means that information in different chapters or sections may follow other guidelines and alternate spelling authorities. For example, occasionally a copyright holder may require that eponymous terms be shown in possessive forms (Crohn’s disease vs. Crohn disease) or that British spelling norms be retained (leukaemia vs. leukemia).

Part 1 | Introduction to Auditory Impairment

Chapter 1 | What Is Auditory System?

Section 1.1 | Basic Principles of Sound

Section 1.2 | Basic Principles of Audition

Section 1.1 | Basic Principles of Sound

This section includes text excerpted from Audiometry Procedures Manual, Centers for Disease Control and Prevention (CDC), January 15, 2016. Reviewed September 2020.

Sound can be defined in the physical sense as a series of pressure waves caused by a vibrating object and propagated through an elastic medium. In other words, sound is initiated when an object begins to vibrate. As the object moves back and forth, it bumps into molecules in the surrounding area, forcing them to move also. These displaced molecules in turn put pressure on other molecules and thus the sound wave is propagated. Because the molecules return to their original resting position following displacement, sound is said to occur in an elastic medium.

In the physiological sense, sound can be defined as the sensation evoked in the auditory system by these pressure changes.

Sound may be characterized along three main parameters: frequency, intensity, and complexity. Frequency is the rate of the sound pressure waves, or how often the molecules are displaced in a given period of time. Frequency is measured in Hertz (Hz), or cycles per second, and is perceived as pitch. Lower-pitched sounds (such as the rumble of traffic or a man’s speaking voice) are lower in frequency; higher-pitched sounds (such as a whistle or a baby’s cry) have higher frequencies.

Intensity refers to the amplitude of the pressure waves, or how far the molecules are displaced from their original position. Amplitude is measured in decibels and is perceived as volume, or loudness. Low amplitude sounds (in which the molecules are displaced only a little bit) are perceived as quiet and high amplitude sounds (in which the displacements are larger) are perceived as loud.

Complexity refers to the interaction of the various frequencies and intensities that make up a sound. For example, a pure tone is a sound that is made up of only one frequency and one intensity. Most sounds are made up of many frequencies at different intensities combined to make a very complex signal. Complexity is perceived as sound quality or timbre. If a flute and violin are playing the same note at the same volume, complexity is the parameter of sound that allows us to distinguish between the two instruments.

Within the context of National Health and Nutrition Examination Survey (NHANES), the CDC is concerned primarily with the frequency and intensity of signals. The human ear is responsive to frequencies from about 20 to 20,000 Hz, but not equally so. It is most sensitive from about 1000 to 3000 Hz; and the frequencies most necessary for the understanding of speech are 500 to 4000 Hz. Audiometry conducted as part of the NHANES will include test frequencies from 500 to 8000 Hz.

Test frequencies in audiometry are derived from the musical scale, and are generally octave intervals. An octave is a tone with a frequency that is exactly twice that of a reference tone. Therefore, the basic audiometric test frequencies are 500, 1000, 2000, 4000, and 8000 Hz. In addition, testing is often done at 3000 and 6000 Hz (sometimes called the inter-octave frequencies) because these frequencies are useful in identifying hearing losses due to noise exposure.

Intensity is a little more complicated. Remember that intensity refers to amplitude, or how far the molecules are displaced from their resting position by the vibrating object that is creating the sound. The farther the molecules are displaced, the greater pressure they place on neighboring molecules. Thus, intensity is measured in units of pressure; the higher the pressure, the louder the sound.

However, the difficulty is that the human ear is responsive to a very wide range of pressures. The pressure of a sound that is just barely audible to a young, normal-hearing listener is approximately 20 μPa. (The μPa—micropascal—is a unit for measuring pressure.) The pressure of a sound that is painfully loud could be about 200,000,000 μPa. Because it is a bit cumbersome to use such a large range to quantify intensity, we convert the pressure measurements to decibels. In decibels, the human ear is responsive to intensities from 0 dB to 140 dB—a much more manageable range.

The decibel scale is logarithmic rather than linear; this means that the difference in actual sound pressure from one decibel to the next increases as the decibel level increases. For example, the increase in pressure from 20 to 40 dB is not the same as the increase in pressure from 40 to 60 dB. Pressure increases by 1800 μPa from 20 to 40 dB, but pressure increases by 18,000 μPa from 40 to 60 dB. Because of the logarithmic nature of the scale, decibels cannot be added and subtracted in the usual way. Two independent sound sources that each have an intensity of 90 dB produce a sound level of about 93 dB when they are put together, not 180 dB.

There are several different decibel scales used in measuring sound and hearing. When measuring sound levels at different frequencies in the environment, the sound pressure level (SPL) scale is used; results are recorded in dB SPL. When measuring an individual’s hearing thresholds, the hearing level (HL) scale is used; results are recorded in dB HL. A measurement of 30 dB SPL is not the same as a measurement of 30 dB HL.

Finally, it is important to note that a measurement of 0 dB does not mean that there is no sound at all—just like a temperature of 0 °F does not mean that there is no heat at all. There are sounds that are quieter than 0 dB, and these sounds are measured in negative decibels in the same way that temperatures colder than 0° are measured in negative degrees.

Section 1.2 | Basic Principles of Audition

This section includes text excerpted from Audiometry Procedures Manual, Centers for Disease Control and Prevention (CDC), January 15, 2016. Reviewed September 2020.

When you think of the ear, you probably think primarily of the two most visible portions of the auditory system that are located on either side of the head. However, the ear is much more than this. The ear actually has four main parts: the outer ear, the middle ear, the inner ear, and the auditory neural system.

The outer ear consists of the auricle (sometimes called the pinna) and the ear canal (also called the external auditory meatus). The outer ear functions primarily to funnel sound into the ear, and to modify, to some extent, the acoustic signal. The shape and size of the ear canal cause it to amplify signals with frequencies of approximately 2000–3000 Hz; this is the main reason that human hearing is most sensitive in this frequency range.

Figure 1.1. Principles of Audition (Source: Ear Infections in Children, National Institute on Deafness and Other Communication Disorders (NIDCD))

The middle ear consists of the eardrum (or the tympanic membrane); three tiny bones (or ossicles) called the malleus, the incus, and the stapes; and two small muscles. The primary function of the middle ear is to transform the acoustic signal into mechanical vibration. The middle ear muscles form part of a reflex arc (known as the acoustic reflex), which provides some small amount of protection against loud sounds. The middle ear also houses an opening to the eustachian tube, which connects this part of the ear to the back of the throat. The eustachian tube permits ventilation of the middle ear space, which maintains a balance in air pressure on either side of the eardrum; this balance is necessary in order for the eardrum to respond to sound most efficiently.

The inner ear consists of the cochlea, which is contained within a spiral opening in the temporal bone of the skull. The cochlea is divided into three parallel, fluid-filled ducts. The upper and lower ducts are connected at one end; and a wave is set up in them as the ossicles vibrate in response to sound. The middle duct contains rows of tiny hair cells. These hair cells are bent as the wave comes to a peak; the bending of the hair cells stimulates the auditory nerve. The inner ear, therefore, serves to transform the mechanical vibrations from the middle ear into neural impulses.

The auditory neural system consists of the auditory nerve and the auditory areas of the cortex. This system carries the neural impulses to the brain and interprets them.

The auditory system is complete and possesses normal adult sensory function approximately half-way through prenatal development. The ability of the auditory neural system to process signals, however, continues to develop for several years. Newborns are able to discriminate sounds on the basis of frequency, intensity, and type of stimulus. (They prefer human speech!) Over the first few months, infants learn to localize, associate hearing with their own vocal productions, and gradually to better and better imitate the vocal sounds of others. By 1 year of age, they are able to process the meaning of approximately 50 words. By age 4, children can process and understand just about everything they hear.

Auditory sensitivity reaches its peak at adolescence and then begins a very gradual decline. Barring any insult that would accelerate the decline (such as noise or disease), the reduction in sensitivity is not generally clinically measurable until at least the third decade of life. After about age 60, hearing sensitivity decreases by an average of about 10 dB per decade. The decrease in hearing sensitivity begins at the highest frequencies and gradually progresses to include the middle and low frequencies. Hearing loss due to age-related changes is called presbycusis.

There are a number of other age-related changes that occur in the ear. The cartilage in the outer ear and the ear canal begins to deteriorate, causing the auricle and canal opening to become very soft; this can cause a condition known as canal collapse, which can affect hearing test results. Additionally, the ear canal narrows and cerumen becomes drier; these conditions combine to impede the natural expulsion of wax from the ear canal. Cerumen becomes more easily trapped, potentially partially or completely blocking the ear canal and causing a temporary loss of hearing. The tympanic membrane may become less flexible and there can be slight degenerative changes in the joints between the bones in the middle ear; however, these issues are typically not significant enough to affect hearing sensitivity.

Chapter 2 | Hearing Loss: An Overview

Section 2.1 | Basics of Hearing Loss

Section 2.2 | Types of Hearing Loss

Section 2.3 | Auditory Loss in Infants and Children

Section 2.4 | Older Adults

Section 2.1 | Basics of Hearing Loss

This section includes text excerpted from Audiometry Procedures Manual, Centers for Disease Control and Prevention (CDC), January 15, 2016. Reviewed September 2020.

Dysfunctions anywhere along the auditory pathway can cause hearing loss. Hearing losses may be divided into several categories based on where in the ear the impairment is located (the type of hearing loss), how severely the impairment affects a person’s hearing sensitivity (the degree of hearing loss), and which ears are affected (the laterality of the hearing loss).

Hearing losses that are caused by a problem in the external or middle ear are called conductive hearing losses, because the difficulty lies in the conduction of sound to the cochlea. For example, excessive wax in the ear canal, fluid in the middle ear brought on by an infection, or a discontinuity between the ossicles would prevent sounds from reaching the inner ear efficiently. These types of hearing losses are often medically or surgically correctable.

Hearing losses that are caused by a problem in the inner ear or along the auditory nerve are called sensorineural hearing losses, because the difficulty lies in the ability of the cochlea to sense the sound or the ability of the nerve to carry the signal to the brain. Damage to the cochlear hair cells due to age-related deterioration, repeated noise exposure, or a tumor on the auditory nerve are examples of etiologies that would lead to sensorineural hearing impairment. These types of hearing losses are not usually medically correctable. Often, sensorineural hearing loss can be remediated to a certain extent with hearing aids. However, while hearing aid technology has improved immensely, they do not restore normal hearing in the same sense that eyeglasses restore normal vision.

Classifying degree of hearing loss is much more complex. The severity of the handicap due to abnormal hearing thresholds depends on a number of interrelated factors, such as the age of the individual, the age at which the impairment was first sustained, the point of damage within the auditory system, the individual’s communicative environment and needs, the presence or absence of other illnesses or sensory deficits, etc. For example, a person who has had significant hearing loss since birth is affected differently than someone who acquires a similar hearing loss after reaching adulthood. A person with a conductive hearing loss (which causes simply a reduction in the audibility of sounds) is affected differently than someone with a sensorineural hearing loss (which often causes a reduction in the intelligibility as well as the audibility of sounds), even if their thresholds are the same. And a person whose only sensory impairment is hearing loss is affected differently than someone with the same hearing thresholds but who also has significant visual or mobility impairments.

Nevertheless, some basic scheme for classifying severity of hearing loss is necessary. Although there is no one universally accepted method of defining degree of hearing loss, the following system is generally representative of the various schemes currently in use:

0–25 dB (Normal hearing)

26–40 dB (Mild hearing loss)

41–55 dB (Moderate hearing loss)

56–70 dB (Moderately severe hearing loss)

71–90 dB (Severe hearing loss)

91+ dB (Profound hearing loss)

Quite often, an individual has different degrees of hearing loss at different frequencies. For example, normal hearing in the low frequencies and gradually worsening hearing sensitivity in the high frequencies is typical of age-related and noise-related impairments. In cases such as these, the classification scheme may be applied to each test frequency individually (e.g., normal hearing sensitivity through 1000 Hz, gradually sloping to a moderately-severe hearing loss at the highest test frequencies); or thresholds at various frequencies may be averaged and an overall hearing loss rating may be assigned. Here again, however, there is little agreement as to which frequencies ought to be averaged. The American Speech-Language-Hearing Association (ASHA) and the National Institute for Occupational Safety and Health (NIOSH) classify hearing impairment according to the average hearing threshold at 1000, 2000, 3000, and 4000 Hz. Other recommendations include average thresholds at 500, 1000, and 2000 Hz or an average of 1000, 2000, and 3000 Hz. Some schemes even involve weighting the various frequencies included in the average. Audiometric results obtained in the National Health and Nutrition Examination Survey (NHANES) will be reviewed by an audiologist who will determine the scheme to be used in classifying degree of hearing loss.

Finally, hearing losses may be classified as either unilateral (affecting only one ear) or bilateral (affecting both ears). Bilateral hearing losses may be symmetric (approximately the same in each ear) or asymmetric (worse in one ear than the other). Hearing losses from environmental causes (such as noise, ototoxic chemicals, and aging) are generally bilateral and symmetric. Hearing losses from medical causes (such as ear infections, mumps, and acoustic tumors) are often unilateral or asymmetric. A substantial difference in hearing sensitivity between ears can, therefore, be indicative of a medically significant condition.

Section 2.2 | Types of Hearing Loss

This section includes text excerpted from Types of Hearing Loss, Centers for Disease Control and Prevention (CDC), June 8, 2020.

A hearing loss can happen when any part of the ear or auditory (hearing) system is not working in the usual way.

Outer Ear

The outer ear is made up of:

The part we see on the sides of our heads, known as pinna

The ear canal

The eardrum, sometimes called the tympanic membrane, which separates the outer and middle ear

Figure 2.1. Inside of the Ear

Middle Ear

The middle ear is made up of:

The eardrum

Three small bones called ossicles that send the movement of the eardrum to the inner ear

Inner Ear

The inner ear is made up of:

The snail-shaped organ for hearing known as the cochlea

The semicircular canals that help with balance

The nerves that go to the brain

Auditory (Ear) Nerve

This nerve sends sound information from the ear to the brain.

Auditory (Hearing) System

The auditory pathway processes sound information as it travels from the ear to the brain so that our brain pathways are part of our hearing.

Four Types of Hearing Loss

Conductive Hearing Loss

Hearing loss caused by something that stops sounds from getting through the outer or middle ear. This type of hearing loss can often be treated with medicine or surgery.

Sensorineural Hearing Loss

Hearing loss that occurs when there is a problem in the way the inner ear or hearing nerve works.

Mixed Hearing Loss

Hearing loss that includes both a conductive and a sensorineural hearing loss.

Auditory Neuropathy Spectrum Disorder

Hearing loss that occurs when sound enters the ear normally, but because of damage to the inner ear or the hearing nerve, sound is not organized in a way that the brain can understand.

Degree of Hearing Loss

Mild Hearing Loss

A person with a mild hearing loss may hear some speech sounds but soft sounds are hard to hear.

Moderate Hearing Loss

A person with a moderate hearing loss may hear almost no speech when another person is talking at a normal level.

Severe Hearing Loss

A person with severe hearing loss will hear no speech when a person is talking at a normal level and only some loud sounds.

Profound Hearing Loss

A person with a profound hearing loss will not hear any speech and only very loud sounds.

Other Ways to Describe Hearing Loss

Unilateral or Bilateral

Hearing loss is in one ear (unilateral) or both ears (bilateral).

Prelingual or Postlingual

Hearing loss happened before a person learned to talk (prelingual) or after a person learned to talk (postlingual).

Symmetrical or Asymmetrical

Hearing loss is the same in both ears (symmetrical) or is different in each ear (asymmetrical).

Progressive or Sudden

Hearing loss worsens over time (progressive) or happens quickly (sudden).

Fluctuating or Stable

Hearing loss gets either better or worse over time (fluctuating) or stays the same over time (stable).

Congenital or Acquired/Delayed Onset

Hearing loss is present at birth (congenital) or appears sometime later in life (acquired or delayed onset).

Section 2.3 | Auditory Loss in Infants and Children

This section includes text excerpted from What Is Hearing Loss in Children? Centers for Disease Control and Prevention (CDC), June 8, 2020.

Hearing Loss in Children

Hearing loss can affect a child’s ability to develop speech, language, and social skills. The earlier children with hearing loss start getting services, the more likely they are to reach their full potential.

Signs and Symptoms

The signs and symptoms of hearing loss are different for each child. If you think that your child might have hearing loss, ask the child’s doctor for a hearing screening as soon as possible. Do not wait!

Even if a child has passed a hearing screening before, it is important to look out for the following signs.

Signs in Baby

Does not startle at loud noises

Does not turn to the source of a sound after 6 months of age

Does not say single words, such as dada or mama by 1 year of age

Turn her or his head when she or he sees you, but not if you only call out her or his name. This sometimes is mistaken for not paying attention or just ignoring, but could be the result of a partial or complete hearing loss.

Seems to hear some sounds, but not others

Signs in Child

Speech is delayed

Speech is not clear

Does not follow directions. This sometimes is mistaken for not paying attention or just ignoring, but could be the result of a partial or complete hearing loss.

Often says, Huh?

Turns the TV volume up too high

Babies and children should reach milestones in how they play, learn, communicate, and act. A delay in any of these milestones could be a sign of hearing loss or other developmental problem.

Screening and Diagnosis

Hearing screening can tell if a child might have hearing loss. Hearing screening is easy and is not painful. In fact, babies are often asleep while being screened. It takes a very short time—usually only a few minutes.

Babies

All babies should have a hearing screening no later than 1 month of age. Most babies have their hearing screened while still in the hospital. If a baby does not pass a hearing screening, it is very important to get a full hearing test as soon as possible, but no later than 3 months of age.

Children

Children should have their hearing tested before they enter school or any time there is a concern about the child’s hearing. Children who do not pass the hearing screening need to get a full hearing test as soon as possible.

Treatments and Intervention Services

No single treatment or intervention is the answer for every person or family. Good treatment plans will include close monitoring, follow-ups and any changes needed along the way. There are many different types of communication options for children with hearing loss and for their families. Some of these options include:

Learning other ways to communicate, such as sign language

Technology to help with communication, such as hearing aids and cochlear implants

Medicine and surgery to correct some types of hearing loss

Family support services

Causes and Risk Factors

Hearing loss can happen any time during life—from before birth to adulthood.

Following are some of the things that can increase the chance that a child will have hearing loss:

A genetic cause.