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What are the four steps that get a sound to your brain?
- creation of a sound source
- vibration of air particles
- reception by the ear
- comprehension by the brain
What is sound?
- the movement or vibration of air particles
- air molecules bump into each other so that the vibration is propagated
What is acoustics?
the study of sound
How do air molecules move?
- the swing back and forth but don't move far (ripples in a puddle)
- disturbed molecules bunch close together causing areas of compression, then spread apart to return to their original locations, causing areas of rarefaction
How can we graph sound transmission?
- waveforms show the position of air molecules responding to a sound source
- X axis = time
- Y axis = displacement from resting point
How do we measure sound?
- the rate of vibration of the sound source is the frequency of sound
- it is the number of complete cycles of to-and-fro motion that occur in one second
What is period?
- the time between successive high or low pressure points
- period = 1/frequency (seconds per cycle)
What is frequency?
- how fast air particles move back and forth (cycles per second)
- frequency = 1/period
How do we measure sound?
- frequency is measure in Hertz (Hz)
- higher frequency sounds have more vibratory cycles per second than low frequency sounds
If a period was .10 seconds, what would frequency be?
- 10 Hz
- the shorter the period, the higher the frequency
What range of frequencies can we hear?
- 20 to 20,000 Hz
- the notes on a piano range from 20 to 4,000 Hz
What are the most important frequency ranges for speech?
500 to 4,000 Hz
What is fundamental frequency?
the predominant frequency in a complex waveform
What happens when the fundamental frequency is doubled?
it increases by one octave
What is a pure tone?
- a vibration at only one frequency
- also called a sine wave
What is a complex wave?
- vibration with multiple frequencies produced by the source
- most things including our speech are complex waves
What does periodic mean?
a sound repeats itself at regular intervals
What does aperiodic mean?
- sound has no repetitive pattern
- white noise is aperiodic
What is intensity?
- the pressure produced by the vibrating motion is intensity
- how far apart the particles move when going back and forth
What is sound pressure leve (SPL) measured in?
- decibels (dB)
- 0 dB SPL is the perfect hearing threshold
What results in higher sound intensity?
greater air molecule displacement
What does a spectrogram do?
helps to analyze frequency, intensity, and timing of sounds
What are the 3 major sections of the ear?
- outer ear
- middle ear
- inner ear
What is the outer ear?
- entry point for sound waves
- the visible part of the ear
What does the outer ear do?
- gathers and funnels sound waves and channels them inward
- protects the interior of the hearing apparatus from being damaged
What is the pinna (auricle)?
the visible part of the outer ear
What are the parts of the pinna?
- lobule- fleshy skin hanging from bottom of pinna
- tragus- hard, cartilaginous triangle that protrudes over the entrance to the auditory canal
- helix- outer body of the pinna
What is the external auditory canal (EAC)?
- a short tube shaped as a loose "s" curve leading to tympanic membrane
- conducts sound waves inward
What is cerumen?
earwax produced by the EAC that traps intruding matter and prevents it from reaching the inner ear
What is the middle ear?
- an air-filed, bony cavity
- transforms acoustic energy to mechanical energy
What are the parts of the middle ear?
- tympanic membrane- ear drum
- ossicles- malleus, incus, stapes
What is the tympanic membrane?
- boundary between outer and middle ears
- air-filled, bony cavity
What is the eustachian tube?
runs from the middle ear to the pharynx and serves as a pressure equalizing tube for the middle ear space
What is the inner ear?
- fluid filled cavity residing in the temporal bone behind the eye socket
- it is a complex system of canals and cavities, somtimes called a labyrinth
- converts mechanical energy to hydraulic energy
What is hydraulic energy?
power created by compressive force or movement of liquid in a confined area
What are the 3 major cavities of the inner ear?
- semicircular canals
Where does the vestibule sit?
between the cochlea and semicircular canals
What are the semicircular canals?
open off one side of the vestibule and consist of three canal systems that serve as the organs of balance
What is the cochlea?
- opens off the other side of the vestibule and consists of a single, fluid filled canal that serves as the organ of hearing
- it is a bony, coiled canal in a snail shape and hard walled and fluid filled
What sets the fluid in the vestibule in motion?
- movement of the stapes on the oval window
- the fluid waves carry the auditory info into the cochlea and stimulate the basilar membrane
What is tonotopic organization?
different places on the membrane are put into vibration with different frequencies of sounds
What is the difference between the base and apex of the basilar membrane?
- the apical end is wider and less stiff
- the apex vibrates mostly to lower frequency sounds and the base to higher frequency sounds
What is the organ of Corti and where is it located?
- a long row of hair cells
- sits on the basilar membrane
What do hair cells of the organ of Corti do?
- they are stimulated by the vibrations of the basilar membrane
- they turn auditory information into neural energy that is transported along the auditory nerve of the brain
What is the auditory nerve?
- a bundle of nerve fibers that exits the cochlea and travels to the brain
- it is part of cranial nerve VIII (vestibulocochlear nerve)
What does the auditory nerve do?
transports auditory information, in the form of neural energy, from the cochlea to the brain stem, the midbrain, and the cerebrum
What does Heschl's gyrus do?
receives speech and language stimuli
What does Wernicke's area do?
involved in linguistic comprehension
What is the auditory cortex?
- processes incoming auditory info that includes both speech and nonspeech
- left = speech and lang. processing within Heschl's gyrus
What is the first 3 steps in the physiology of hearing?
- sound waves are directed by the pinna into the ear canal
- waves strike the eardrum and cause it to vibrate
- the eardrum is connected to the malleus, which moves the ossicles back and forth (this is the mechanical part of the process)
What are the last 4 steps in the physiology of hearing?
- the movement of the footplate of the stapes makes waves in the fluid of the cochlea (this is the sensory part of the process)
- pressure of the waves causes the basilar membrane to vibrate, moving the hair cells in the organ of corti
- the movement of the hair cells generates nerve impulses
- the nerve impulses are passed on to the 8th nerve and transmitted to the auditory area of the brain
What is air conduction?
sound waves travel through the air to the outer ear (starting at the pinna) and are transmitted through the middle ear to the cochlea
What is bone conduction?
- vibrations of bone cause movement in the fluids of the inner ear
- the larger bones of the skull conduct sound because they vibrate in response to airborne sound waves
- we normally hear our own voice through a combination of air-bone conduction sounds
What is pediatric hearing loss?
when a child or adolescent is unable to detect or distinguish the range of sounds normally available to the human ear
How does hearing loss vary?
- location of damage
- which ear(s) are damaged
- time of onset
What are the locations of the ear that can be damaged?
- auditory nerve
What does chronicity refer to?
- short term (ear infection, after a concert)
- long term (grows worse over time)
What does origin refer to?
- could be due to genetics
- or acquired (illness, injury, trauma)
Tim of onset?
- congenital (present at birth)
- prelingual (soon after birth but before a child has developed language)
- postlingual (after language skills are well established)
What happens if HL is not detected early?
- it will result in delayed receptive and expressive speech, and language development (vocab development, use of grammatical morphemes, pragmatic skills, phology can all be negatively impacted)
- children with HL may achieve one to four grade levels less than peers with normal hearing, and the gap may widen over time
How can hearing loss be classified according to severity?
- using the decibel (dB) system
- normal, mild, moderate, moderately severe, severe, profound
What is an audiogram?
- hearing level in decibels plotted on a graph
- Y axis = dB and loudness perception
- X axis = frequency range
What is the speech banana?
- it shows where different speech sounds are located perceptually for different dimensions of pitch and amplitude
- you need to have a hearing threshold of below 25 dB SPL at 4,000 Hz to hear fricatives
What is conductive hearing loss (CHL)?
- a condition in which sound is not "conducted" efficiently through the outer or middle ear, resulting in attenuation of outside loudness
- exaggerates the loudness of the individual's own voice because of bone conduction of sound vibrations
How serious is CHL?
- does not typically result in severe HL because sounds still travel to the brain via bone conduction
- often temporary because it is amenable to surgical or medical intervention
What is otitis media?
- a viral or bacterial infection of the middle ear space characterized by eustachian tube dysfunction, fluid buulid up, middle ear swelling, and perforated TM
- most common cause of CHL in children
What can be used to fight an ear infection?
- pressure equalizing tubes can be inserted through the eardrum to equalize pressure in middle ear and release fluids
Why is otitis media so common in children?
- the angle and short length of the eustachian tube makes it easier for organisms to enter and move through the tube
- some environmental allergens
- group child care children are at higher risk (3x more likely)
- cerumen blockage, foreign objects, swimmer's ear, malformations of outer or middle ear
What is sensorineural hearing loss (SNL)?
- a HL resulting from damage to the cochlea or auditory nerve that travels from the cochlea to the brain
- results in a decrease in loudness as well as a decrease in speech perception and decreased ability to distinguish speech from background noise
What can SNHL result from?
- causes related to genetics, pregnancy, postbirth disease or injury
- often the cause is unknown (50%)
How is SNHL treated?
hearing cannot usually be restored, but it can be treated through amplification and other interventions
What is mixed hearing loss (MHL)?
- occurs when both conductive and sensorineural loss occurs simultaneously
- MHL includes a permanent reduction in sound, as well as an additional temporary loss
- for example, a child with a congenital SNHL may acquire a CHL from a bout of otitis media
How is pediatic HL identified?
- aural habilitation evaluation
- hearing aid evaluation
- comprehensive audiological evaluation
- infant hearing screening (or) conventional hearing screening
- newborn screenings are completed at birth before the child leaves the hospital
What are the components of a comprehensive audiological evaluation?
- case history and interview
- other interviews and observation
- otoscopic examination
- objective measures
What is an otoscope?
- a lighted magnifying device used to evaulate the structure of the outer and middle ear
- the audiologist inspects the auditory canal and tympanic membrane with an otoscope
- can reveal if there is negative pressure behind the TM, whether the ME is infamed, and if there is fluid in the ME
What happens when the TM is rectracted?
What happens when the TM appears red?
What happens when the line of fluid is discernable through the transparent membrane?
fluid in the ME
What is audiometry?
- also called pure-tone testing
- provides objective information about hearing acuity
What does audiometry involve?
- the child to respond to tones, requiring the child's cooperation and participation
- thresholds are obtained for each frequency and are graphed on an audiogram
What can air conduction tests do?
provide info about the functioning of the outer and middle ear
What can bone conduction tests do?
provide info about the functioning of the cochlea and the auditory nerve
What determines if somebody has a CHL?
- bone conduction thresholds are normal but diminished air conduction thresholds
- there is a significant air-bone gap (air thresholds problematic but bone thresholds are ok)
- cochlea and auditory nerve are still functioning
- abnormality in outer or middle ear
What determines if somebody has a SNHL?
- decresase in hearing threshold in both air and bone conduction as frequency increases
- no air-bone gap
What determines a mixed HL?
- combination of sensorineural and conductive loss
- both air and bone conduction thresholds are diminished AND there is a significant air-bone gap
- bone conduction testing problematic, but better than air conduction
What is tympanometry?
- examines tympanic membrane movement or vibration
- evaluates hearing without requiring infant or child to respond
What is otoacoustic emissions (OAE's)?
- detected and recorded in ear canal
- when cochlea is impaired, OAEs are abnormal or absent
What is evoked auditory potentials (EAPs)?
provide information about the auditory pathway
How is pediatric HL treated?
- ASL or spoken English choices
- education (mainstream or hearing impaired school?)
- amplification devices (hearing aids, assistive listening devices, cochlear implants)
Types of hearing aids
- behind the ear- most common for kids
- in the ear
- in the ear canal
What are assistive listening devices (ALDs)?
- FM systems- can be used in noisy situations or with distant speakers
- improve a person's hearing ability in difficult listening situations
- surgically placed device that provides electrical stimulaion to the auditory nerve
- 12% use cochlear implants
How do cochlear implants work?
- microphone converts acoustic to electrical signal
- signal transmitted through skin to an internal receiver implanted in mastoid bone
- signal is transmitted to electrodes in the cochlea which then deliver sound to the auditory nerve
What is aural habilitation?
- required for children with HL learning to use oral language
- ensuring an appropriate listening environment by minimizing auditory distractions
- maximize audition by maintaining the quality of the ALD
- adults should enhance the acoustic signal to provde more audible cues during interactions
- support listening development by coupling auditory and visual cues and gradually increasing auditory demands
What is early intervention?
- single most important factor in determining long-term achievement for children with HL
- intervention for infants, toddlers, and preschoolers
What are interventions for infants, toddlers, and preschoolers?
- parental involvement to expose children to language learning opportunities
- naturalistic environments to facilitate carryover
- support development within the context of authentic social interactions
- develop capacity for functional communication in everyday contexts
What are interventions for school-age children?
- an effective means of communication must be established (signs with oral language or cochlear implant)
- self-advocate outside home
- consistent and intensive support to achieve literacy and literate thought
What are auditory processing disorders (APDs)?
- neurological problem that adversely affect an individual's processing, or interpretation, of auditory messages, even though hearing acuity is intact
- little difficulty with speech production, but vocab development, pragmatics, listening, and academic achievement may be affected
- amplification is not an option becaus difficulties are not related to hearing acuity
How many Americans have HL?
- more than 31 million
- 10% of the population
- over 1/4 of the adult population will experience a HL in their lifetime
- 90% of persons over the age of 80 have hearing loss
Why do adults often resist seeking treatment for HL?
- perception that HL is not severe enough
- costs for treatment
- negativity about hearing aids
- hearing screenings occur infrequently at routine medical visits
What is the most common HL in adults?
- cochlea and auditory nerve most affected by aging, noise exposure, illness, disease, and injury
What is presbycusis?
HL that occurs as a result of age
What other effects can hearing loss have on a person?
- social-emotional (higher rates of depression, etc)
What are the most common causes of adult HL?
- noise exposure/damage
- head trauma
- ototoxic drugs
What are the severity ranges of HL?
- mild (26-40 dB)
- moderately severe
- profound (>91 dB)
- normal hearing is -10-25 dB)
What are cause of conductive HL in adults?
- cerumen blockage
- foreign objects in ear canal
- otitis media
- damage to outer or middle ear
- otosclerosis (abnormal bone growth around ossicles)- 2:1 ratio of women to men
What sounds are most affected by hearing loss?
- consonants, particularly voiceless fricatives
What are causes of SNHL in adults?
- noise-induced HL results from exposure to damaging level of noise (greater than 85 dB)
- meniere's disease and tinnitus
- acoustic neuromas- tumors on the auditory nerve
- meningitis, cerebral-vascular disease, diabetes, etc
What is ototoxicity?
taking ototoxic drugs can damage the hearing mechanism
How is adult HL treated?
- a comprehensive plan combining:
- fitting of amplification devices
- aural rehabilitation
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