There are three common types of hearing losses. They are (1) conductive, (2) sensorineural, and (3) mixed (i.e. conductive and sensorineural). There are two other hearing losses that have to deal with interpretation of sound (refer to Section 2 of this module). They are (1) a central auditory processing loss, and (2) a functional hearing loss.

Conductive, Sensorineural, and Mixed Hearing Losses

The first three losses primarily are concerned with the perception of sound. Sound perception is determined by the degree and severity of the hearing loss. Typically a hearing loss is measured by the frequency and intensity of the sound. The frequency of sound is called hertz (Hz). The intensity of the sound is called decibel (dB). The severity of the hearing loss depends on where the hearing loss occurs, the age of onset, age of discovery, location of the hearing loss (i.e. unilateral or bilateral), and the type of condition that the learner has (e.g., syndrome, medication, etc.).

Central Auditory Processing and Functional Hearing Losses

The other two hearing losses primarily are concerned with the interpretation of sound. A central auditory processing loss means that the sound waves travel through the appropriate channels, are transmitted to the brain by the VIIIth Auditory Nerve to the auditory cortex. This is where the sound may get mixed up as the brain receives the message.

The functional hearing loss is similar in that the sound is transmitted through the sections of the ear, transforms mechanical energy to electrical impulses as it passes along the VIIIth Auditory Nerve to the auditory cortex. Once it reaches the auditory cortex there is some difficulty with interpretation of the message. What makes a functional hearing loss so controversial is that little research has been conducted to verify what a functional hearing loss is and there is no standardized measurement in which to detect this type of hearing loss.

The following information describes in greater detail the types of hearing losses, the range of hearing losses, and the severity of the hearing losses. The remaining questions in this module will address the causes of hearing loss, medical and educational assessments, and environmental adaptations, modifications, and supports to help learners who are deaf or hard of hearing participate in their home, school and community environments.

Hearing Losses of Conduction, Perception, and Interpretation

As mentioned at the beginning of this question, there primarily are three types of hearing losses that effect the conduction, perception, and interpretation of sound. They include:

Conductive. A conductive hearing loss occurs in the outer or the middle sections of the ear. It effects the conduction of sound. A conductive hearing loss impedes sound waves from traveling to the inner ear. This type of hearing loss can be caused by:

(1) malformation of the outer ear structures (e.g., ear canal) and middle ear structures (e.g., oscicle bones),

 

(2) wax in the ear canal,

 

(3) scar tissue around the tympanic membrane (i.e. ear drum),

 

(4) infections (e.g., chronic otitis media-ear infections), or

 

(5) age (e.g., otosclerosis). It usually is an acquired type of hearing loss that generally can be corrected surgically.

 

The following illustrations are various examples of ear infections and ear anomalies.

Source: Google Images, http://www.google.com

Symptoms of a learner who has a conductive hearing loss will have a tendency to speak softly. He may complain of tinnitus (i.e. ringing in the ears). A learner with a conductive hearing loss usually does not have difficulty with speech discrimination even when conversation occurs in a large amount of environmental noise. Since a learner with a conductive hearing loss generally hears better when others increase the volume of their voices, he can discriminate speech sounds without being affected by environmental noise. On occasion, high frequency sounds are easier for the learner to hear than low frequency sounds.

Sensorineural. A sensorineural loss occurs in the inner ear. It primarily affects the perception and interpretation of sound. A sensorineural loss prevents the transformation of sound waves from mechanical energy to electrical energy as it travels along the VIIIth Auditory Nerve to the auditory cortex in the brain. Additionally, a sensorineural loss also can affect balance if there is a malformation of the vestibular apparatus or the semicircular canals.

A learner with a sensorineural hearing loss often will speak louder than necessary to the point that it is uncomfortable for other people to hear her. A typical learner hears her own speech through bone conduction (e.g., middle ear). However, a learner with a sensorineural loss does not hear her voice through bone conduction since the problem is in the inner ear or the VIIIth Auditory Nerve. Additionally, a sensorineural loss can cause a loss of speech discrimination of sounds. Typically, a learner with a sensorineural loss hears the lower frequency sounds better than the higher frequency sounds.

Mixed. A mixed hearing loss means the learner has both types of hearing losses; conductive and sensorineural. The learner with a mixed loss has some difficulty with bone conduction, but he has greater difficulty with air conduction. A mixed loss often occurs in older adults, but occasionally can be found in younger learners. For example, an older adult may have presbycusis (e.g., hairs in the Organ of Corti become stiff with age) and otosclerosis (e.g., bones in the middle ear become less flexible with age). A younger learner who has a mixed hearing loss may have chronic otitis media in the middle ear (e.g., middle ear infection) and distortion of the cochlea in the inner ear (e.g., misshapen).

Functional Hearing Losses

As discussed earlier in this section, there are two types of hearing losses that affect interpretation of sound. They are:

Central auditory processing loss. A central auditory processing loss is a disturbance between the auditory pathways after the information travels along the VIIIth Auditory Nerve to the auditory cortex. Sometimes there is not a disturbance in the pathways as the information travels to the auditory cortex. However, once the information reaches the auditory cortex, the brain has difficulty interpreting the information that was sent. Some of the more common causes of central auditory processing losses occurs by abscess, vascular changes, or tumors in that area of the brain.

Functional hearing loss. Controversy surrounds the definition of what factors determine a functional hearing loss. In traditional audiological texts, a functional hearing loss is central to psychological functioning (e.g., pseudohypacusis). However, to those educators who work with learners with deafblindness, functional hearing loss does not have a psychological component. Many educators believe that a functional hearing loss is synonymous with learners who have a cortical visual impairment.

As with learners who have cortical visual impairments, in learners with functional hearing losses, sound travels through the outer, middle, and inner ear with full functioning of all of the bones and structures of the inner ear, and then travels along the VIIIth Auditory Nerve to the auditory cortex of the brain. When the information reaches the auditory cortex, it does not know how to interpret the information that has been received most of the time. However, it may be able to interpret the information some of the time.

There are several factors that influence the interpretation of sound when it reaches the auditory cortex. The factors are the differences in skills to detect sounds and to discriminate sounds. This is due to the complexity of sounds since they occur at different frequencies using different levels of energy. Essentially, if the brain can not hear all aspects of energy in sounds, it will have difficulty in differentiating between sounds as well as difficulty in discriminating sounds. Some learners are able to fill in the blanks that occur when they are not able to differentiate or discriminate between sounds based on the context of the conversation and the experience the learner has with speech and language.

The Kansas Project for Children and Youth who Are Deaf-Blind Guidelines for Certifying Infants, Toddlers, Children, and Youth (2001) define functional hearing loss as,

. . . "functionally deaf," "cortically deaf," or "central auditory processing loss" - the hearing structures are present and working; however, the student does not attend, respond, localize, or process hearing to receive information from the environment or accurately interpret information about the environment on a consistent basis (p. 5).

Other states identify functional hearing in terms of the remaining residual hearing instead of considering it as a loss. For example, a learner who has functional hearing means that his or her residual hearing with amplification is sufficient to understand auditory information.

Currently, research is being conducted by the Texas Tech University and Louisiana State University on what constitutes a functional hearing loss and how a functional hearing loss for learners who are deafblind is tested. For more information about functional hearing loss and the testing of functional hearing loss refer to Section 5 in this module.

The Severity of Hearing Losses

The severity of a learner with a hearing loss varies across different sources in the literature. Essentially the severity of a learner with a hearing loss is determined by degree of the loss and understanding speech and/or environmental sounds. As stated previously in this section, the intensity or loudness of sounds is measured in decibels and across frequencies. The tables listed below illustrate the variance among different measurements and descriptions of hearing loss based on the intensity of sounds.

Table 1

Severity and Degrees of Hearing Loss

Heller, K. W., & Kennedy, C. R. (1994). Etiologies and characteristics of deaf-blindness. Monmouth, OR: Teaching Research.

Table 2
Intensity of Sound Expressed in Decibels

Whaley, L. F., & Wong, D. L. (1989). Nursing care of parents and children. St. Louis, MO: Mosby Year Book, Inc.

To gain a better understanding of the effects that hearing losses have on a learner's ability to perceive and interpret speech and environmental sounds, refer to the audiogram below. This audiogram depicts the intensities and frequencies of which different sounds are heard and understood. Additionally, speech sounds are located in the area that looks like a banana. This area frequently is referred to as the speech banana. (Refer to section five for information about audiograms.)

The Speech Banana

info@gohear.org

Task for Completion and Discussion #3:

Find two additional resources that depict the severity, degrees, and levels of hearing losses. Compare those resources with the above listed resources. Describe the similarities and the differences between the degrees and levels from the additional resources to the ones in the above listed tables. Then, describe how the severity and degree of hearing loss impacts the learning of a learner who is deafblind. (Hint: Refer to the online module Introduction to Learners Who are Deaf-Blind.)

For More Information:

If you would like further information about the types and severity of hearing losses, some of the below listed resources may be useful to you.

AudiologyNet

http://www.audiologynet.com/index.html

Click on the link that is associated with your topic.

American Speech Language Hearing Association: Types of Hearing Loss

http://www.asha.org/public/hearing/disorders/types.htm

Click on the link that is associated with your topic.

The Kansas Project for Children and Youth Who are Deaf-Blind:

Infants, Toddlers, Children, and Youth Certification Guidelines

http://www.ksde.org

Scroll down the menu on the left to Special Projects.

Click on the link that is associated with your topic.

DB Link

http://www.tr.wou.edu/dblink/lib/topics/topics.cfm

Click on DB Library.

Click on the link that is associated with your topic.

Hearing Loss

http://www.dizziness-and-balance.com/disorders/hearing/hearing.html

Click on the link that is associated with your topic.