Introduction to Clinical Masking in Audiology
Channel: Greg O'Beirne
Date: 2022-05-05

This is an introductory lecture for undergraduate speech therapy students on Clinical Masking in Audiology. By the end of this session, you should:
• understand the mechanisms of cross hearing, how the size of this effect (interaural attenuation) differs with different transducers, and the problem this poses for the measurement of hearing thresholds.
• understand the use of masking to prevent the non-test ear from responding, the stimuli used for this, and how it is calibrated (as "dB effective masking").
• understand the terms undermasking, the masking plateau between the minimum and maximum masking levels, and overmasking.
• be able to describe the occlusion effect and how to avoid it.
• be able to describe how a shadow curve may arise in pure-tone audiometry.
• understand the underlying rationale for the masking rules for air, bone, and speech.
• understand the masking dilemma and how we can sometimes address it.

0:00 Introduction
1:21 Refresher on bone conduction mechanisms
4:34 Bone conductors stimulate the test ear *and* the non-test ear
5:45 Cross hearing with bone conduction
8:23 Cross hearing with air conduction
10:21 Interaural attenuation
11:49 Impact of cross hearing on audiometric testing
14:13 Advantages of using insert earphones
15:25 Interaural attenuation of insert earphones
18:29 Why do we need masking?
20:35 Masking definitions
23:10 Clinical masking using an audiometer
27:42 Effective masking level (dB EM)
29:07 Undermasking, masking plateau (minimum and maximum levels), overmasking
33:56 Masking procedures (quick overview)
35:27 Bone conduction masking example
40:50 The occlusion effect
42:39 Avoiding the occlusion effect
44:00 Shadow curves
46:21 Masking rule #1 - When to mask for air conduction
49:31 Masking rule #2 - When to mask for bone conduction
52:03 Masking rule #3 - When to mask for speech
54:52 The masking dilemma

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