By Marlee Henderson and Heather Schieffler

How Do We Hear?

In order for us to hear, sound waves travel through the ear canal and vibrate the eardrum which passes those vibrations through small bones in the middle ear to the cochlea, a snail-shaped structure of the inner ear¹. The cochlea then translates the vibrations into electrical signals that are transmitted up the auditory (hearing) nerve to the brain.

What is Sensorineural Hearing Loss?

There are two main types of hearing loss - Conductive and Sensorineural. Conductive
hearing loss occurs when sound is unable to be transmitted through the ear canal to the eardrum
and small bones of the middle ear². Sensorineural Hearing Loss (SNHL) is a hearing impairment caused by damage to the cochlea or auditory nerve³. As explained in the following video, tiny hair cells in the cochlea of the inner ear perceive sound and transmit it to the auditory nerve, which then carries the
information to the brain to be processed and understood⁴.

Causes of Sensorineural Hearing Loss

SNHL has a variety of causes and can be either congenital, meaning present during pregnancy or at the time of birth, or acquired at any time in one’s life after birth⁵.

Congenital Causes:

• Infections during pregnancy such as rubella, toxoplasmosis, syphilis, and
• cytomegalovirus among others
• Genetic syndromes including (but not limited to) Alport, Waardenburg, and Usher syndrome
• Prenatal drug exposure
• Oxygen deprivation during birth
• Trauma to the head during birth
• Prematurity⁵.

Acquired Causes:

• Chronic Ear Infections
• Meningitis
• Measles
• Mumps
• Inflammation of the brain (encephalitis)
• Chickenpox
• Influenza (the flu)
• Exposure to loud noise for prolonged periods of time
• Side effects of some medications
• Head injury⁵.

Levels of Hearing Loss

Hearing is evaluated by measuring the sound intensity level (loudness) that can be heard using the units decibels Hearing Level (dB HL)⁶. For children, the degrees of hearing loss are categorized as follows:

-10 to 15 dB HL normal hearing range
16 to 25 dB HL slight or borderline hearing loss
26 to 45 dB HL mild hearing loss
50 to 65 dB HL moderate hearing loss
70 to 90 dB HL severe hearing loss
91+ dB HL profound hearing loss⁶

The following video simulates hearing at each degree of hearing loss. Make sure you do not adjust the volume on your speakers once it begins:

Click HERE for the video: “What Hearing Loss Sounds Like”

Identifying Children with Hearing Loss

Approximately 3 infants per 1,000 are born with moderate, profound, or severe hearing loss making it one of the most frequently occurring birth defects⁷. Hearing loss is even more common in infants admitted to intensive care units at birth⁸. Because hearing examination data is lacking for children 0-5 years old, newborn hearing screening data was used to estimate congenital hearing loss at a prevalence of 30,000 children under the age of six⁸.

Undetected and/or untreated hearing loss can delay speech, language, and cognitive development and can result in significant educational costs and learning difficulties⁷. The National Center for Hearing Assessment and Management (NCHAM) has reported that detecting and treating hearing loss at birth for one child can saves $400,000 in special education costs by the time that child graduates from high school⁷.

Louisiana legislation dictates that all newborn infants are required to receive a hearing screening prior to discharge from the hospital⁷.

The Effects of Hearing Loss on Speech

SNHL limits the capability to hear faint sounds and can also distort sounds so they are not heard correctly⁹. Children with profound hearing loss or deafness will have insufficient development of auditory skills including:

• Auditory speech perception - the ability to perceive and understand speech
• Speech production - the ability to produce speech
• English Language skills - the ability to use and understand reading, writing, and speaking, as well as the ability listen¹⁰

Without the assistance of a hearing aid or cochlear implant, residual hearing, which is the small amount of hearing remaining in the presence of SNHL, is typically insufficient due to the effect of distortion on speech sounds, and the lack of acoustic cueing--the ability to differentiate sounds³. Some children with profound hearing loss are able to acquire practical communication skills by using conventional aids, but most do not¹⁰.

What are Cochlear Implants?

According to ASHA¹¹, “a cochlear (koe-klee-er) implant is a device that provides direct electrical stimulation to the auditory nerve in the inner ear” (para.1). Implantation of a cochlear device allows sound to bypass damaged inner hair cells and directly stimulate the auditory nerve¹¹. Cochlear implants may help children with SNHL that do not benefit from hearing aids that amplify and direct sound through the ear canal.

Who Can Get Cochlear Implants?

Cochlear implants have been approved by the U.S. Food and Drug Administration for use in children with severe to profound SNHL in both ears and who get limited benefit from hearing aids starting at 12 months of age⁸. Generally, a hearing loss measured at 90 dB HL or above indicates candidacy for cochlear implantation¹⁰. As of 2012, approximately 38,000 children in the United States were implanted with cochlear devices, with 324,000 children registered with implants worldwide⁸.

Benefits of Cochlear Implants

Research has shown that speech perception, speech production, and speech intelligibility (the “understandability” of speech) improve in children with cochlear implants as compared to their non-implanted peers who use hearing aids¹⁰. Children who receive cochlear implants between 6 to 12 months typically demonstrate significant progress in vocabulary development, and receptive and expressive spoken language abilities¹⁰. In those children deafened before developing language skills (pre-lingually), continual progress in speech recognition and speech production has been shown after the cochlear implants are received¹⁰. Overall, sound detection and auditory perception improve after receiving cochlear implantation¹⁰.

Citations

¹U.S. Department of Health and Human Services, National Institutes of Health, National Institute
on Deafness and Other Communication Disorders. (2015). How do we hear?. Retrieved
from https://www.nidcd.nih.gov/health/how-do-we-hear

²American Speech-Language-Hearing Association. (n.d.). Conductive hearing loss. Retrieved
from http://www.asha.org/public/hearing/Conductive-Hearing-Loss/

³Halliday, L. F., Tuomainen, O., & Rosen, S. (2017). Auditory processing deficits are sometimes
necessary and sometimes sufficient for language difficulties in children: Evidence from
mild to moderate sensorineural hearing loss. Cognition, 166 139-151. doi:10.1016/
j.cognition.2017.04.014

⁴[Siemens]. (2014, August 5). Hearing loss [Video File]. Retrieved from https://
www.youtube.com/watch?v=2rhRo73F324&feature=youtu.be

⁵American Speech-Language-Hearing Association. (n.d.). Causes of hearing loss in children.
Retrieved from http://www.asha.org/public/hearing/Causes-of-Hearing-Loss-in-Children/

⁶DeBonis, D. A., & Donohue, C. L. (2008). Survey of audiology: Fundamentals for audiologists
and health professionals (2nd ed.) Boston, MA: Pearson Education, Inc

⁷National Conference of State Legislatures. (2011). Newborn hearing screening laws. Retrieved
from http://www.ncsl.org/research/health/newborn-hearing-screening-state-laws.aspx

⁸U.S. Department of Health and Human Services, National Institutes of Health, National Institute
on Deafness and Other Communication Disorders. (2005). Statistical report: Prevalence
of hearing loss in u.s. children. Retrieved from https://www.nidcd.nih.gov/workshops/
statistical-report-prevalence-hearing-loss-us-children/2005#sup3

⁹Nelson, W. N. (2010). Language and literacy disorders: Infancy through adolescence. Boston,
MA: Pearson.

¹⁰American Academy of Audiology. (n.d.). Cochlear implants in children. Retrieved from https://www.audiology.org/publications-resources/document-library/cochlear-implants-children

¹¹American-Speech Language-Hearing Association. (n.d.-b). Cochlear implants. Retrieved from
http://www.asha.org/public/hearing/Cochlear-Implant/