"Audiograms Made Easy"

Pure-tone audiometry

• – behavioral test measure used to determine hearing sensitivity
• – tests peripheral and central auditory systems
• – Pure-tone thresholds (PTT’s) indicate:
• • softest sound audible to an individual at least 50% of the time
• • plotted on an audiogram

Audiogram

Chart of hearing sensitivity

• abscissa ⇔ frequency (range 250–8000 Hz)
• - represents most of speech spectrum
• - human ear can detect frequencies from 20–20,000 Hz
• - children can detect even higher frequencies
• ordinate ⇔ intensity

Intensity: level of sound power measured in decibels; loudness is the perceptual correlate of intensity.

Hearing level (HL): measured in decibels (based on the standardised average of individuals with normal hearing sensitivity).

Air Conduction

Signal is transmitted through the outer, middle, and inner ear and then through the brain to the cortex. May be performed using headphones, insert earphones, or sound fields.

Bone Conduction

Assesses sensitivity when the signal is transmitted through the bones of the skull to the cochlea and then through the auditory pathways of the brain. Bypasses the outer and middle ear.

Bone-conduction oscillator:

• – small oscillator is placed on mastoid.
• – stimulates the bones of the skull, which in turn stimulates both cochleae.

Masking

Masking presents a constant noise to the nontest ear to prevent crossover from the test ear. The purpose of masking is to prevent the nontest ear from detecting the signal, so only the test ear can respond.

Speech Discrimination

Ability to repeat correctly an open set of monosyllabic words at suprathreshold intensity. Word lists are phonetically balanced (PB), i.e., the speech sounds used occur with the same frequency as in the whole language.

Types of Hearing Tests

Pure Tone Audiometry – Adults

• • Hearing is measured with pure tones through headphones.
• • Loudness of each tone is reduced until the patient can just hear the tone.

Hearing Tests for Young Children

Behavioral Observation Audiometry (BOA)

• - infants < 7 months of age
• - noisemaker testing

Visual Reinforcement Orientation Audiometry (VROA)

• • children between 7 months and 3 years
• • altering frequency and intensity of sounds ⇒ assesses ability to hear across a range of frequencies

Play Audiometry

• • children > 3 years of age
• • child listens to sounds and is taught to make a response every time a sound is heard

Hearing Levels

• 10–20 dB = Normal range
• 21–40 dB = Mild hearing loss
• 41–55 dB = Moderate hearing loss
• 56–70 dB = Moderately severe hearing loss
• 71–90 dB = Severe hearing loss
• > 90 dB = Profound hearing loss

Types of Hearing Loss

Conductive hearing loss ("mechanical")

• blockage or damage to outer +/- middle ear
• – perforated tympanic membranes
• – fluid in the middle ear system
• – scarring of tympanic membrane

Sensorineural hearing loss ("electrical")

• damage or malfunction of the sensory part (cochlea) or the neural part (auditory nerve)
• congenital or acquired

Mixed hearing loss

• problem in both conductive pathway (outer or middle ear) and nerve pathway (inner ear or nerve)
• – e.g., CHL due to a middle-ear infection combined with a SNHL due to aging

Abbreviations

Tympanometry

Measures compliance of middle ear

• Normal (Type A)
• Hypermobile TM (high peak – Ad)
• Decreased TM mobility (shallow peak – As)
• Flat (Type B) – OME or perforation
• Negative middle ear pressure (Type C)

Other Tests

Oto-acoustic Emission Testing (OAE)

Measures function of outer hair cells in the cochlea. They respond to sound by producing a very soft sound of their own called oto-acoustic emission.

Brainstem Evoked Response Audiometry (BERA) / Auditory Brainstem Response (ABR)

Provides information on electrical activity generated in response to sound stimulus along the nerve pathway, brainstem, and cerebral cortex. < 6 months old (may be carried out in natural sleep); > 6 months old (under sedation in hospital).