Clinical Masking in Audiology

Comprehensive vocabulary flashcards covering the core concepts, transducer values, formulas, symbols, and clinical rules for air-conduction and bone-conduction audiometric masking.

Clinical Masking

The use of noise delivered to the non-test ear to accurately obtain ear-specific hearing test results, often required in cases of unilateral or asymmetric hearing loss.

Test Ear (TE)

The ear for which the clinician is attempting to establish true hearing thresholds, specifically isolating its cochlea.

Non-Test Ear (NTE)

The ear that must not hear the stimulus presentation; it receives masking noise to prevent its cochlea from responding to sound intended for the test ear.

Cross Over

The acoustic phenomenon where sound presented to one ear travels across the head to the opposite cochlea, occurring either through skull bone vibrations (bone conduction pathway) or sound leakage around the transducer seal.

Interaural Attenuation (IA)

The loss of acoustic energy that occurs when sound crosses over from one side of the head to the opposite ear, which depends on the transducer type.

Interaural Attenuation for Supra-Aural Headphones

The conservative energy loss across the head when using standard headphones, established at $40\,\text{dB}$.

Interaural Attenuation for Insert Earphones

The conservative energy loss across the head when using insert earphones, established at $60\,\text{dB}$.

Interaural Attenuation for Bone Conduction

$0\,\text{dB}$, because the bone oscillator vibrates the entire skull, stimulating both cochleas simultaneously with theoretically no energy loss.

Shadow Curve

A false audiogram configuration where the unmasked air-conduction thresholds of a poorer ear falsely mirror the shape of the better ear at an intensity separated by the interaural attenuation value.

Narrow Band Noise (NBN)

The specific type of masking noise used during pure-tone audiometry, centered around the test frequency and presented via the same transducer.

Effective Masking Level

The amount of noise sufficient to raise the non-test ear's threshold above the level of crossover so responses are guaranteed to be from the test ear, without crossing back over to the test ear.

Overmasking

A state where excessive masking noise is presented to the non-test ear such that it crosses back over the skull to the test ear, falsely worsening the threshold being tested.

Masking Dilemma

A situation where the minimum effective masking level needed to isolate the test ear is high enough to cause overmasking, typically seen in bilateral conductive hearing losses.

General Masking Delivery Rules

Masking noise is ALWAYS delivered to the non-test ear (NTE) and is ALWAYS delivered via air conduction.

When-to-Mask Rule for Air Conduction

Masking is required whenever the air-conduction threshold of the test ear minus the bone-conduction threshold of the non-test ear exceeds the interaural attenuation ($\text{AC}_{\text{TE}} - \text{BC}_{\text{NTE}} > \text{IA}$).

Minimum Masking Level Formula (Air Conduction)

$$\text{Presentation Level}_{\text{TE}} - \text{IA} + \text{ABG}_{\text{NTE}}$$

Maximum Masking Level Formula

$$\text{BC}_{\text{TE}} + \text{IA}_{\text{masking transducer}} - 5\,\text{dB}$$

When-to-Mask Rule for Bone Conduction

Masking is required whenever the air-conduction threshold of the test ear and the unmasked bone-conduction threshold show an air-bone gap of $15\,\text{dB}$ or greater ($\text{AC}_{\text{TE}} - \text{Unmasked BC} \ge 15\,\text{dB HL}$).

Occlusion Effect (OE)

The artificial improvement of bone-conduction thresholds, primarily at low frequencies, caused by trapping and amplifying reverberating sound energy inside a closed ear canal when occluded by headphones or inserts.

Occlusion Effect Values for Headphones

$20\,\text{dB}$ at $500\,\text{Hz}$ and $10\,\text{dB}$ at $1000\,\text{Hz}$.

Occlusion Effect Values for Insert Earphones

$10\,\text{dB}$ at $500\,\text{Hz}$ and $0\,\text{dB}$ at $1000\,\text{Hz}$.

Minimum Masking Level Formula (Bone Conduction)

$$\text{BC Presentation Level}_{\text{TE}} + \text{ABG}_{\text{NTE}} + \text{OE}$$

Masked Air Conduction Symbol (Right Ear)

A triangle (red, $\Delta$), denoting that the right ear was the test ear and the left ear received masking noise.

Masked Air Conduction Symbol (Left Ear)

A square (blue, $\Box$), denoting that the left ear was the test ear and the right ear received masking noise.

Masked Bone Conduction Symbol (Right Ear)

A bracket opening to the right ($[$).

Masked Bone Conduction Symbol (Left Ear)

A bracket opening to the left ($]$).