Speaker identifies as a speech-language pathologist (SLP) with a Ph.D. focused on speech and hearing sciences.
Clarification that they are not a clinical audiologist and will reference external materials for specialized depth.
Inclusion of short instructional videos to provide visual modeling of audiological procedures and anatomical processes.
Chapter Four: Pure Tone Audiometry and Masking
Overview of Pure Tone Audiometry
The Testing Environment: Conducted in a sound-treated booth designed to minimize ambient noise.
Audiology Schematic: Includes an audiologist controlling the audiometer from a separate workspace and the patient receiving stimuli.
Patient Participation: Detection of pure tones across a frequency range (typically 250 Hz to 8000 Hz).
Developmental Considerations:
Adults: Typically provide a physical response (button press or hand raise) and may participate in speech testing (repeating words).
Children: Responses are often conditioned through play or visual reinforcement to maintain engagement.
Equipment Used in Audiometry
Audiometers: Devices used to deliver precise frequencies and intensities. Modern clinics increasingly utilize computer-based audiometers for automated data collection and integration with Electronic Health Records (EHR).
Transducers: Components that convert electrical energy into sound, including supra-aural headphones, insert earphones, and bone oscillators.
Air Conduction Audiometry
Pathways: Sound travels through the outer ear, middle ear, and finally to the inner ear and auditory nerve.
Objective: To determine the Threshold, defined as the lowest intensity level in decibels (dB HL) where a patient can detect a sound 50\% of the time.
Transducer Options:
Supra-aural earphones: Placed over the pinna; standard but can cause ear canal collapse in some patients.
Insert earphones: Placed inside the canal; better at reducing ambient noise and preventing ear canal collapse.
Limitations: Results identify the degree of hearing sensitivity but cannot distinguish the specific site of lesion (outer/middle vs. inner ear).
Interpretation of the Audiogram
Audiometric Zero: The level at which a healthy young adult can just barely hear a sound (0 dB HL).
Classification of Hearing Loss (Adults):
Normal: -10 to 25 dB HL
Mild: 26 to 40 dB HL
Moderate: 41 to 55 dB HL
Moderately Severe: 56 to 70 dB HL
Severe: 71 to 90 dB HL
Profound: > 90 dB HL
The Air-Bone Gap (ABG): The numerical difference between air conduction and bone conduction thresholds. An ABG greater than 10 dB suggests a conductive component.
Bone Conduction Audiometry
Mechanism: A bone oscillator (placed on the mastoid process or forehead) vibrates the skull to stimulate the cochlea directly, bypassing the outer and middle ear.
Diagnostic Utility:
Conductive Hearing Loss: Bone thresholds are normal (\le 25 dB HL), while air thresholds are abnormal, indicating the problem is in the outer/middle ear.
Sensorineural Hearing Loss: Both air and bone thresholds are equally abnormal (within 10 dB of each other), indicating damage to the cochlea or auditory nerve.
Mixed Hearing Loss: Both air and bone thresholds are abnormal, but bone is significantly better than air (ABG exists).
Masking in Audiometry
The Necessity of Masking: Prevents "cross-hearing," where a sound presented to the test ear is loud enough to vibrate the skull and be detected by the non-test ear.
Clinical Rules for Masking:
Interaural Attenuation (IA): The loss of energy of a sound as it travels from one side of the head to the other.
For supra-aural headphones, IA is 40 dB; for insert earphones, IA is roughly 60 dB.
Procedure: Narrowband noise is introduced to the non-test ear to "keep it busy" while the test ear is evaluated.
Behavioral Responses in Audiometry
Behavioral Observation Audiometry (BOA)
Target Group: Infants from birth to approximately 6 months.
Responses: Passive reflexive behaviors, such as the sucking reflex changes, startle responses (Moro reflex), or eye-widening.
Limitations: High variability; thresholds are often higher than true hearing sensitivity.
Visual Reinforcement Audiometry (VRA)
Target Group: Toddlers between 6 months and 2 years.
Method: The child is conditioned to turn their head toward a sound source; upon doing so, a visual reward (flashing toy or video) is activated.
Effectiveness: Provides highly reliable ear-specific thresholds if performed with insert earphones.
Conditioned Play Audiometry (CPA)
Target Group: Children aged 2.5 to 5 years.
Method: The child performs a motor task every time they hear a sound (e.g., dropping a block in a bucket, putting a peg in a board).
Engagement: Relies on social reinforcement and turning the test into a repetitive game to ensure cooperation.
Conclusion
Audiological assessment is a multifaceted process requiring different strategies depending on the patient's age and developmental level.
Integration of air conduction, bone conduction, and behavioral observations allows the SLP and Audiologist to form a comprehensive picture of a client's hearing health.