LING 209 Auditory System Diseases

• Diseases of the auditory system are covered in Diagnostic Audiology as part of LING 209.
• The presentation date is March 24, 2025.

Typical Hearing

• In a typical hearing assessment, "O" marks the right ear, "X" indicates the left ear, and "S" denotes a speaker.
• It is estimated that ~7% of American adults have normal audiograms but experience challenges with speech in noise.

Hearing Loss

• 15% of individuals over 18 in the USA have a hearing loss
• 90-95% of those with hearing loss could be helped with hearing aids.
• Hearing loss can lead to academic, workplace, and psychological-social challenges like loneliness, depression, and anxiety.
• 0.2 - 0.3% of infants are born with hearing loss.
• 7.4% of 29-40 year-olds have hearing loss.
• 14.6% of 41-59 year-olds have a hearing problem.
• Hearing loss affects 30% of people over 60.

Audiologists

• According to the American Academy of Audiology, audiologists provide services in the auditory identification, assessment, diagnosis, and treatments.
• They assist with the vestibular function of people with impairments and act as clinicians, therapists, teachers, consultants, researchers, and administrators.
• Audiology uses technology, and audiologists must be technologically skilled.

Assessing Hearing

• Assessment include behavioural, psychoacoustic, and electrophysiologic measures of peripheral and central auditory system.
• The vestibular system is assessed via behavioural and electrophysiologic tests of equilibrium (balance).

Vertibular Assessment

• Maintaining posture, coordinating movements, and tracking visual targets involves integrating the vestibular, visual, somatosensory (touch, temperature, body position), and cerebellar systems.

Vertigo

• Vertigo indicates a peripheral vestibular disorder.
• Dizziness or balance issues arise from central nervous system problems, medication, or psychological factors.
• Around 35% of adults and 5.3% of children experience dizziness and/or balance problems.

Vestibular System Assessments

• Vestibulo-ocular reflex (VOR) connects the brainstem's vestibular neural pathway to neurons controlling eye muscles. It helps maintain a clear visual image during head movement.
• Vestibulospinal reflex (VSR) connects the vestibular nuclei in the brainstem to motor neurons that control skeletal muscles. This helps control the body when unexpected changes in position occur relative to gravity.
• VNG detects balance by infrared video tracking eye movements. An individual's rapid eye movements (nystagmus) are measured.
• Individuals are strapped to a chair in a dark room, like an "amusement ride", in a process called rotary chair.
• Rotary chair measures rapid eye movements using VNG.
• Data from both VNG and rotary chairs are compared to standard data.
• Differences in eye movement gain, phase, and symmetry are examined.
• Posturography assesses balance by changing vestibular, visual, and somatosensory inputs while standing on a platform that measures weight distribution.
• VEMPs measure myogenic potentials from high-intensity low-frequency tones recorded from the neck or ocular muscles. This gauges the vestibulo-collic (VCR) and vestibulo-ocular reflexes (VOR).

Hearing Evaluation

• Steps include case history with the patient, otoscopy, immittance, acoustic reflex threshold, audiometric testing, and physiological responses.

Otoscopy

• Otoscopy detects cerumen (ear wax), foreign objects, and disorders of the outer and middle ear.

Immittance

• It indicates opposition to sound, provided by the acoustic and mechanical properties of the outer and middle ear.
• A middle ear with fluid has greater impedance than a healthy ear.
• Admittance measures energy flow through the middle ear. This is part of the conductive hearing system.
• Tympanometry determines immittance with a 226 Hz tone usually presented at 85 dB.
• During tympanometry, the ear canal is pressurized, and in a healthy ear maximum admittance occurs at 0 daPA.

ART

• Acoustic reflex threshold (ART) employs the same equipment as tympanometry.
• ART measures the contraction of the stapedius muscle in response to loud sounds to decrease admittance.

Otoacoustic Emissions

• Otoacoustic Emissions is a common hearing screening tool for newborns that tests cochlear function.
• In a functioning cochlea, outer hair cell movement creates pressure fluctuations, creating otoacoustic emissions. During the test, a plug in the ear presents sound and records the emitted sound

Auditory Brainstem Response (ABR)

• It presents broadband clicks to the ear, and separates the neural response from electrical noise.

Frequency Following Response (FFR)

• Measures the brainstem's response to frequency.
• Speakers of tonal languages have more accurate FFRs.

Audiometric Testing

• It is the "mainstay" for testing includes pure tone audiometry (thresholds for pure tones) and speech audiometry (thresholds for spoken language).
• Frequencies from 250 – 8000 Hz are used.
• The goal is identifying the softest intensity for a particular tone heard 50% of the time.
• An audiometer generates sine waves from 125 Hz to 8000 Hz in octave or half-octave steps.
• The air conduction is when sound is presented with earphones or ear inserts. Bone conduction sound presented via a bone oscillator that vibrates the skull to access the cochlea
• The air-bone gap size can be used to identify conductive hearing loss.

Speech Audiometry

• It establishes speech reception threshold and measures speech recognition ability above threshold.
• These tests use pre-recorded speech.
• Speech reception threshold finds the lowest intensity that provokes a response.
• Familiarized spondee words are used.
• Spondee words are two syllable words with roughly equal stress on each syllable.

Word Recognition

• Single syllable words reflect the rate of occurrence.
• Patients repeat words out loud. Higher level above audiometry thresholds means patient has better word recognition skills.

Speech in Noise

• Most audiometry tests are done in quiet conditions.
• SNR or signal-to-noise ratio is tested.

Masking

• Energetic masking occurs when frequencies of noise overlap frequencies in the signal.
• Informational masking occurs if the background noise is understandable.

Summary

• A range of tests and tools in an audiologists arsenal assess:
  • The vestibular system
  • Hearing through air conduction
  • Hearing through bone conduction
  • Sensorineural encoding of auditory stimuli
  • Performance with tones and speech