HIS Pure Tone & Speech Audiometry 2 — Questions and Answers

Question 1: What is a bone conduction audiogram used to determine?

The patient's ability to discriminate speech
The cochlear and neural reserve of the auditory system, bypassing the outer and middle ear (Correct answer)
The hearing aid gain required
The tympanic membrane compliance

Correct answer: The cochlear and neural reserve of the auditory system, bypassing the outer and middle ear

Bone conduction testing delivers sound vibrations directly to the cochlea via a bone oscillator placed on the mastoid or forehead, bypassing the outer and middle ear to assess sensorineural reserve.

In bone conduction audiometry, a bone oscillator placed on the mastoid process vibrates the skull and directly stimulates the cochlear fluids. Comparing air conduction (AC) and bone conduction (BC) thresholds reveals the type of hearing loss: if AC equals BC (no air-bone gap), the loss is sensorineural; if AC is worse than BC (air-bone gap of 10 dB or more), there is a conductive component. This distinction is critical for differential diagnosis and referral decisions.

Question 2: A patient's audiogram shows air conduction thresholds of 50 dB HL and bone conduction thresholds of 15 dB HL at 2000 Hz. What type of hearing loss does this indicate?

Sensorineural hearing loss
Conductive hearing loss (Correct answer)
Mixed hearing loss
Normal hearing

Correct answer: Conductive hearing loss

An air-bone gap of 35 dB (50 dB AC minus 15 dB BC) with normal bone conduction indicates a conductive hearing loss, meaning the outer or middle ear is impeding sound transmission to an otherwise functional cochlea.

When bone conduction thresholds are within normal limits (25 dB HL or less) but air conduction thresholds are elevated, the difference (air-bone gap) reveals a problem in the outer or middle ear. A 35 dB air-bone gap at 2000 Hz strongly suggests a conductive pathology such as otosclerosis, otitis media with effusion, or ossicular chain disruption. This patient should be medically referred before hearing aid fitting.

Question 3: What does the Speech Recognition Threshold (SRT) measure and how does it relate to the pure tone average (PTA)?

The ability to understand speech in noise; it should be 20 dB better than PTA
The lowest level at which the patient can correctly repeat 50% of spondee words; it should agree within 10 dB of the PTA (Correct answer)
The maximum speech intelligibility score; it is unrelated to PTA
The loudness discomfort level for speech; it is 30 dB above PTA

Correct answer: The lowest level at which the patient can correctly repeat 50% of spondee words; it should agree within 10 dB of the PTA

SRT is the hearing level at which a patient correctly identifies 50% of spondee (two-syllable, equal stress) words. It should agree within 10 dB of the PTA (average of 500, 1000, 2000 Hz thresholds) as a validity check.

The Speech Recognition Threshold (SRT) uses spondee words (e.g., baseball, hotdog, airplane) because their equal syllable stress makes them predictable. A correctly conducted SRT should agree within plus or minus 10 dB of the pure tone average (PTA). If the SRT is significantly better than the PTA, it may indicate functional or non-organic hearing loss where the patient is exaggerating their thresholds on the pure tone test. This discrepancy flags the need for additional testing.

Question 4: What is the purpose of masking in audiometry?

To reduce patient anxiety during testing
To prevent the non-test ear from responding to sounds presented to the test ear, ensuring thresholds reflect only the test ear (Correct answer)
To calibrate the audiometer
To test hearing in background noise conditions

Correct answer: To prevent the non-test ear from responding to sounds presented to the test ear, ensuring thresholds reflect only the test ear

Masking introduces a noise (usually narrowband noise) into the non-test ear to prevent it from detecting cross-heard sounds intended for the test ear, ensuring that thresholds reflect only the ear being tested.

Sound presented to one ear can cross the skull and stimulate the opposite cochlea—this is called cross-hearing or transcranial transmission. Without masking, if the test ear has a severe loss, the non-test ear may respond, giving falsely better thresholds for the poor ear. Interaural attenuation for insert earphones is about 70-80 dB for air conduction and approximately 0 dB for bone conduction, meaning masking is almost always required for bone conduction testing.

Question 5: What pure tone average (PTA) threshold range defines a moderate hearing loss?

16-25 dB HL
26-40 dB HL
41-55 dB HL (Correct answer)
56-70 dB HL

Correct answer: 41-55 dB HL

According to standard audiometric classification, moderate hearing loss falls in the 41-55 dB HL range. Patients in this range typically have significant difficulty understanding speech without amplification.

Standard audiometric severity categories classify hearing loss as: normal (25 dB HL or less), mild (26-40 dB HL), moderate (41-55 dB HL), moderately severe (56-70 dB HL), severe (71-90 dB HL), and profound (91+ dB HL). Patients with moderate loss struggle with conversational speech, especially at distance or in noise, and almost universally benefit from hearing aid amplification.

Question 6: Which test is used to assess the acoustic reflex and can help identify middle ear pathology or auditory nerve dysfunction?

Pure tone audiometry
Speech in noise testing
Acoustic immittance testing (tympanometry and acoustic reflex testing) (Correct answer)
Distortion product otoacoustic emissions (DPOAEs)

Correct answer: Acoustic immittance testing (tympanometry and acoustic reflex testing)

Acoustic immittance testing includes tympanometry (middle ear pressure and compliance) and acoustic reflex testing (stapedius muscle contraction in response to loud sounds), helping identify middle ear pathologies and retrocochlear disorders.

Acoustic immittance testing is a battery of objective tests. Tympanometry measures the compliance of the tympanic membrane as ear canal air pressure is varied, revealing middle ear conditions such as negative pressure, effusion, ossicular discontinuity, or perforation. The acoustic reflex tests stapedius muscle contraction triggered by loud sounds; absent reflexes can indicate facial nerve lesions, retrocochlear pathology, or middle ear problems. These tests do not require patient behavioral responses.

HIS Pure Tone & Speech Audiometry 2

What is a bone conduction audiogram used to determine?