Hearing Measurement 2

• Lecture 2 covers Pure-Tone Audiometry by Dr. Steve J. Aiken, Dalhousie University, 2025.
• It addresses why thresholds are measured, the strange nature of speech perception, and the role of detail in hearing.

Measuring Thresholds

• Measuring thresholds helps understand the softest sounds audible at different frequencies.
• This is important because speech perception relies on subtle details within a broad spectrum.
• Hair cells in the inner ear respond to specific frequencies.
• On the loudness graph, 5 mm is equal to an octave.
• One mm is equal to one band.

Frequency Specificity

• Frequency-specific tones and low sound pressure levels are both important for accurate place specificity in hearing tests.
• Place specificity is only possible if frequency specific tones and low sound pressure levels are used

Importance of Audiometry

• Audiometry is important, shown with an audiogram sample with reference to right and left ear frequencies and hearing levels
• Audiometry can reveal various issues, from ear canal problems to brain tumors.
• Performance in real-life listening environments depends on auditory processing and cognitive factors.

The Audiogram

• An audiogram displays hearing thresholds across different frequencies, indicating hearing sensitivity
• The audiogram includes a graph of familiar sounds and where they fall in relation thresholds

Role of Outer and Middle Ear

• The average pressure gain of the external ear is related to ear canal acoustics
• Acoustic gain components include the spherical head, torso and neck, concha, pinna flange, and the ear canal/eardrum.
• The outer and middle ear amplify sound pressure, with specific gain limits for stiffness and mass.

dB SPL to dB HL

• dB SPL is transformed to dB HL (Hearing Level)
• RETSPL is the reference equivalent threshold sound pressure level and refers to the level of average threshold.
• The average is subtracted so that average is zero.

Thresholds

• Threshold is the level at which a tone is heard 50% of the time, indicating the softest audible sound.
• Hit rate is calculated by #hits / #tones

Audiometer Components

• An audiometer includes a presentation control, attenuator, singal router, oscillator, and noise generator
• Also includes talk forwar level: level of your voice when talking to the patient
• Buttons include a talk forward button and an interrupt button
• Test Selection: allows the user to choose the stimulus type, adjust intensity levels, select masking options, and route signals for testing.
• Monitoring and Adjustment
• Routing and Masking
• Madsen Astera and GSI AudioStar are examples of clinical audiometers, while Shoebox Audiometry is an example of automated equipment

Testing Environment

• The testing environment also matters
• Important to control ambient noise
• Permissible ambient noise sound pressure levels in octave bands for audiometric testing are provided for both supra-aural and insert earphones.

Air Conduction Audiometry

• Air conduction audiometry assesses hearing through earphones
• Transducer choices include TDH 49/50 headphones and ER-3A/ER-3C insert earphones.

Transducer Choice

• Speakers are used to test sound field hearing

Dial Readings

• Dial readings provide information about the patient's hearing levels
• KEMAR Manikin is a dummy head used for testing

Bone Conduction Audiometry

• Bone conduction audiometry is completed with a Bone Oscillator
• Bone conduction stimulates the cochlea via fluid inertia and osseotympanic mechanisms

Types of Hearing Loss

• AC measures earphone of speaker, BC measures with Bone Oscillator
• AC-BC calculates the Air-Bone Gap
• The Air-Bone Gap helps distinguish between conductive, sensorineural, and mixed hearing losses.
• Conductive hearing loss occurs in the outer or middle ear.
• Sensorineural hearing loss occurs in the inner ear.

Describing Hearing Loss

• Degree: Normal, Mild, Moderate, Moderately Severe, Severe, or Profound.
• Configuration: describes the shape of the hearing loss across frequencies (e.g., sloping, rising, flat, notched).
• Onset: Congenital (present at birth), Acquired (happens after birth), Adventitious (external source, not innate)
• Time course: Acute, Chronic, Sudden, Gradual, Fluctuating
• Describing Loss: Percentages (AMA)
• Describing Loss: Pure Tone Average

Audiogram Procedures and Symbols

• Audiogram Symbols red=right ear, round. Blue = left ear x
• Bone symbol looks like ears from your perspective
• VT Is vibrotactile and S is soundfield

Testing Arrangement

• Testing Arrangement can be screening or diagnostic
• Transducer Placement by a trained professional is important during audiometry

Test Protocol: Obtaining AC Audiogram

• Begin in better ear first, check levels to see if similar, and if they are use 40-60 dB HL to bgein
• Start at 1000Hz for 1-2 secs
• If no response, increase by 20dB until 80db
• Follow "down 10 up 5" rule
• 50% detection (2/4 or 3/6 repsonses) determines threshold level
• See if improvements
• Test each frequency and compare results
• If >20db difference between frequencies, test frequency between intervals
• Test other ear. Then test bone conduction
• False Responses: patients have false positives, false negatives. Be vigilient for appropriate actions.

Patient Reponses

• Causes tinnitus, equipment error, tester error
• It is important for the patient to present stimuli rhythmically
• Give patient A WAY OUT to help with tester error

Explore audiological tests like Weber, Rinne, and Bing to diagnose hearing loss. Understand the significance of test results in identifying conductive or sensorineural hearing impairments. Also learn about importance of frequency-specific tones and low sound pressure levels in audiology.