Hearing Changes Hearing Changes Throughout the LifespanThroughout the Lifespan

Ashley Webb

HearingHearingIs a primary sense that allows us

to communicate with the world around us.

Human hearing ranges from 20 to 20,000 Hz, with greatest sensitivity at 1 to 4 kHz.1

Hearing Development in Hearing Development in InfantsInfantsThe development of the auditory

system begins to develop at conception.

However, throughout the first half of the pregnancy the fetus is unresponsive to sound

Infants cont.Infants cont.The first elicited response to

sound occurs around 24 to 25 weeks of gestation

Response to sound can be found consistently at 28 weeks.

They concluded that hearing is established as a functionally interactive sensation by the start of the third trimester

It is also thought that with this information gross deafness can be diagnosed in the womb

How We HearHow We Hear44……Sound waves travel through the air and

enter the external auditory canal. They make contact with the tympanic

membrane, which begins to vibrate. The vibrations are then amplified through

the ossicles of the middle ear to the cochlea.

The vibrations create a wave within the fluid in the cochlea.

The mechanical energy of the wave is then transmitted to the hair cells, which turn the mechanical energy into electrical impulses

they then travel through the cochlear nerve to the brain.

Parts of the Human EarParts of the Human Ear55

Waves into Language….Waves into Language….Central Auditory Pathway is

involved in complex processing of sound into recognizable language and music.

Cochlear nerve -> moves through the cochlear nuclei, -> superior olivary complex, -> inferior colliculus,-> through the medial geniculate body-> before finally ending in the auditory cortex

Hearing LossHearing LossHearing loss can start as young

as the 4th decade.

However, it is much more common to see changes in the 6th & 7th decades.

By 2050, more than 86 million adults in the United States (20.7% of the population) will be age 65 and older.4

PresbyacusisPresbyacusis4,64,6

Hearing loss that is gradual and progressive and that accompanies age

most common cause of acquired sensorineural hearing loss in adults

Usually diagnosed by the fact it is gradual, bilateral, and symmetric hearing loss

Effects of PresbyacusisEffects of Presbyacusisdiminishes an individual’s ability

to communicate effectively

presents a safety concern

jeopardizes autonomy

increased incidence of clinical depression and social isolation

3 types of hearing loss3 types of hearing loss77

Sensorineural

Conductive

Mixed

To Test for Hearing LossTo Test for Hearing LossAir conduction (sound waves

traveling to the tympanic membrane)

Bone conduction (sound transmitted via the vibration of the skull).

Rinne Test

Weber Test

Hearing Loss due to the Outer Hearing Loss due to the Outer EarEar

All hearing loss related to the outer ear is by nature a conductive hearing loss.

Congenital

Trauma

Tumors

Middle Ear Hearing LossMiddle Ear Hearing LossMiddle ear consists of: the tympanic

membrane, the ossicular chain, and the middle ear space.

*Just as in the outer ear, all hearing loss is conductive hearing loss.

CongenitalInfectionTympanic Membrane Perforation

Hearing Loss due to Inner Hearing Loss due to Inner EarEarDisorders of the inner ear normally cause a

sensorineural hearing lossassociated with the cochlea, eighth cranial

nerve, internal auditory canal, or brain

Congenital◦ Mondini malformation-the normal 2.5 turns of

the cochlea are replaced by 1 to 1.5 turnsPresbyacusis InfectionNoise ExposureBarotrauma Iatrogenic

Aging and speech-on-Aging and speech-on-speech maskingspeech masking99

Study by Helfer & Freyman

Compared a group of younger normal hearing individuals, and a group of older adults with varying degrees of hearing sensitivity

4 types of maskers: two-talker masker consisting of voices of

the same sex as the target voice, voices of the opposite sex as the target a signal-envelope-modulated noise derived

from the two-talker complexspeech-shaped steady noise

ResultsResultsolder adults had significantly poorer

performance in the presence of all four types of maskers, with the largest absolute difference for the same-sex masking condition.

“A number of age-related cognitive changes have the potential to adversely affect older adults' ability to resolve such complex listening situations”

“ample evidence that aging brings about a reduced ability to ignore irrelevant information (e.g., Hasher & Zachs, 1988; Kausler, 1982; Wright & Elias, 1979); and/or difficulty discriminating relevant from irrelevant information”

Age-related differences in Age-related differences in auditory evoked responses auditory evoked responses during rapid perceptual during rapid perceptual learning learning 1010

Perceptual learning occurs when two stimuli that at first appear identical become differentiated with practice.

In some instances, young and older adults perform a task with equal proficiency but use different networks of brain regions.

This suggests that older adults’ brains undergo large-scale neuroplastic alterations to compensate for age-related changes.

ResultsResultsthe learning rates did not differ

significantly between young and older adults.

Although age-related decline in hearing thresholds likely contributes to the overall difference in performance, it does not prevent older adults from learning

auditory perceptual learning was not significantly affected by age

aging appeared to have only a minor impact on listeners’ ability to quickly learn how to separate and identify concurrent sounds

Application to PT PracticeApplication to PT PracticeKnowing normal development

milestones for infants includes full hearing capability at birth

Realizing hearing changes can take place anytime during the lifespan

However, especially being aware of hearing and brain processing changes in geriatric patients

Knowing how to test for air conduction and bone conduction hearing loss

ConclusionConclusion Hearing is developed while still in utero and is identifiable

by 28 weeks gestation so hearing is completely formed by birth

Hearing changes can occur throughout life if due to trauma or other events

However, overall childhood through middle adulthood (40 years old) hearing is usually intact, individuals are considered to have hearing in the normal ranges of frequency

Starting around the 4th-6th decades of life hearing loss starts occurring with loss in the higher frequencies usually first, this is known as Presbyacusis

Whenever a hearing loss is suspected, an audiogram is essential.

Knowing different hearing changes and how it effects our patients can help make us better clinicians.

ReferencesReferences1 Lasky, R, Williams, A. The Development of the auditory

system from conception to term. NeoReviews. 2005; 6: 3:e141.

2 Birnholz , JC, Benacerraf, BR. The development of human fetal hearing. Science, 1983; 222: 4623: 516-518.

3 Uziel, A. Non-genetic factors affecting hearing development . Acta Oto-Laryngologica. 1985; 99:421: 57-61.

4 Huang, T. Age-related hearing loss. Minnisota Medical. 2007;90(10):48-50.

5 www.humanillnesses.com. May 13, 2008. 6 Bouccara, D, et al. Presbyacusia. American Journal of Otology.

2000;21(6):819-825. 7 Weber,K, Klein, A. Hearing loss. EMC- Oto-rhino-laryngologie.

2005; 2:4: 329-342. 8 Tremblay,K, Ross, B. Effects of age and age-related hearing

loss on the brain. Medical Clinics of North America. 1999; 83:1: 125-137.

9 Helfer, K, Freyman, R. Aging and speech-on-speech masking. Ear Hear. 2008;29(1):87-98.

10 Alain, C, Snyder, S. Age-related differences in auditory evoked responses during rapid perceptual learning. Clinical Neurophysiology. 2008;119(2):356-66

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