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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4612_Библиотеки_им_академика_М_И_Перельмана
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Audiology Review: Preparing for the Praxis and Comprehensive Examinations
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TABLE 3–1. Binaural Advantage Table
BINAURAL TASK ADVANTAGE AUTHORS
Loudness summation (noise) Doubling Marks (1980)
Absolute threshold (noise) 2–3 dB Pollack (1948)
Absolute threshold (tonal stimuli) 2–3 dB Shaw et al. (1947)
Threshold in noise 0–2 dB Hirsh (1948)
Intensity discrimination ~60% improvement Jesteadt and Wier (1977)
Frequency discrimination ~60% improvement Jesteadt and Wier (1977)
Speech (speech recognition threshold) ~2.5 dB Shaw et al. (1947)
it arrives to both ears at the same intensity; however, if the signal moves off to one side or
the other (even by 1°), these higher-frequency sounds will arrive at a higher intensity to the
ipsilateral ear. The contralateral ear will receive a lower-intensity signal (as much as 20 dB
lower at 6 kHz and higher) due to the absorption and reflection of sound around the head
and torso (i.e., shorter wavelengths deflect away from the contralateral ear while longer
wavelengths will “wrap around” the head and torso). Across different frequencies and stimuli,
humans are able to detect IID/ILDs as little as 0.5 to 3 dB.
n
Lower-frequency information (<1500 Hz) will be affected by ITD/IPDs for localization.
These occur because of the time (maximum of 600 µs between ears) it takes for the signal
to reach the contralateral ear, which also translates into a different phase of the signal
arriving to the contralateral as opposed to the ipsilateral ear. A difference in the cochlear
and central transmission of the auditory signal can help a listener identify the location of a
sound source.
Greatest ITD/IPDs are present at approximately 90° and 270° (directly to the right or left,
respectively).
AUDIOLOGY NUGGET
Most, if not all, prescriptive HA formulae (i.e., NAL-NL2, DSL, IHAFF, and
manufacturer specific) prescribe increased gain in cases of monaural fittings.
This is accounts for the lack of binaural input and reduced loudness perception
associated with a monaural fitting. An additional amount of gain (ranging from
3 to 10 dB depending on the input level) is often prescribed in these instances.
Newer HA technology has begun taking advantage of binaural cues by pairing
the aids together and transferring data between them to help in gain adjustments, localization cues, and speech in noise enhancements.
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MAF vs. MAP Curves
Human auditory sensitivity varies by frequency and method of presentation (headphones or speakers).
When auditory sensitivity is evaluated through a speaker, the results are referred to as the minimum
audible field (MAF) curve. Signals presented through headphones provide what is known as the
minimum auditory pressure (MAP) curve. These curves were derived many years ago by measuring
auditory sensitivity (by frequency) for thousands of otologically normal listeners. Figure 3–15 provides
an example of the sensitivity by frequency of the MAF and MAP.
n
Sensitivity shown on the MAF curve is approximately 6 dB better than that shown on
the MAP curve. This is often referred to as the “missing 6 dB.” However, in practical
terms, this is most likely to be a 2 to 3 dB difference at maximum when accounting
for specific recording parameters and accounting for the reflective effects of the head
commonly referred to as the head-related transfer function (Yost, 2013). As such, about
half of the 6 dB difference is related to the binaural advantage and the remainder created
by calibration effects.
Effects of Frequency and Amplitude on Loudness Perception
The perception of loudness varies across the range of audible frequencies. These are visualized via
phon curves and are often referred to as equal loudness contours (Figure 3–16). Horizontal lines
along the equal loudness contours visually represent each phon level (10–120 phon). At any point
along a single curve, the perceived loudness of that tone will be judged to be of equal loudness to
a 1000 Hz tone on that same curve. Of note, at higher intensities, the phon curve is flatter, suggesting more equal perception of loudness across frequencies at higher intensities than at lower
intensities.
FIGURE 3–15. MAP vs. MAF curve. Source: Adapted from Hearing Science
Fundamentals, Second Edition (pp. 1–370) by Lass, N. J., & Donai, J. J.
Copyright © 2023 Plural Publishing, Inc. All rights reserved.
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FIGURE 3–16. Equal
loudness contours
(phon curves).
Source: Adapted
from Hearing
Science Fundamentals, Second Edition
(pp. 1–370) by Lass,
N. J., & Donai, J. J.
Copyright © 2023
Plural Publishing, Inc.
All rights reserved.
AUDIOLOGY NUGGET
The ability to discern minimal differences in intensity is often measured using a
just noticeable difference (JND) task that involves comparing loudness or pitch
between two sounds (a standard sound and comparison sound). The outcome
is often referred to as the difference limen for intensity (or difference limen for
frequency if measuring JND for frequency). Weber’s law is relevant to discussions of the detection of changes in perceived loudness. In short, Weber’s law
(or applied as the Weber fraction) states that a change in a perceived attribute
(e.g., brightness, weight, loudness) is directly proportional to the magnitude of
the original stimulus or object. In other words, if the magnitude of the original
stimulus or object is low (e.g., a dull light, soft sound, or light [weight] object),
a small change in magnitude is discernible between the two. If the magnitude
is high (e.g., a bright light, loud sound, or heavy object), a larger change in
magnitude is required to detect a change. Imagine a classroom with the lights off
(low number of lumens). When someone turns on a flashlight in the front of the
room, the increased light from flashlight is easily detected because the original
magnitude is low. Imagine the same situation with the lights on (higher number
of lumens), with the same flashlight lit. It is likely that the extra light due to
the flashlight will go undetected because the original magnitude of the light is
high. Similarly, a change from 20 to 21 dB SPL is typically discernible, whereas
a change from 80 to 81 dB SPL is not.
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Auditory Recruitment and Outer Hair Cell (OHC) Function
Recruitment is characterized by an abnormal growth of perceived loudness. Due to a loss of OHC
function (the active mechanism/cochlear amplifier), soft sounds are inaudible and thus require increased
intensity to reach threshold; loud sounds are perceived to be approximately as loud as they would be
to individuals with normal hearing or at levels reported prior to hearing loss. The perceptual result of
recruitment is a reduced dynamic range, which is often described as the intensity difference between a
listener’s threshold and his or her uncomfortable listening level. These values are often obtained using
a process called loudness scaling commonly used during the fitting of HAs or CIs.
n
Reductions in dynamic range cause specific problems for fitting HAs. Listeners with
recruitment require more gain for low-level sounds, due to the loss of the OHC active
mechanism, and less gain for moderate to loud sounds.
n
One processing feature in current HAs to account for this need is called wide dynamic range
compression (WDRC). WDRC attempts to account for the loss of OHC function associated
with sensory hearing loss by quickly providing more gain for soft inputs and less gain for
increasingly louder signals. This reduces the need for the patient to consistently increase and
decrease the volume of the HA.
n
WDRC adjusts the gain of the device automatically once the HA is programmed to account
for differences in input levels and the patient’s loudness needs.
KNOWLEDGE CHECKPOINT
Recall that WDRC provides increased gain for lower-level inputs and less gain as
input levels increase. While this is beneficial for maintaining comfort and more
normal perception of loudness, this difference distorts the natural interaurallevel differences present without amplification. Imagine the level of sound at
the right ear being 55 dB SPL and due to the head shadow effect, the level of
the same sound being 45 dB SPL at the left ear (a 10 dB difference). WDRC
will provide more gain for the sound arriving at the left ear (where the sound is
45 dB, i.e., 10 dB less than the right ear). Less gain is provided for the sound
at the right ear (due to a higher input level of 55 dB). Thus, the original 10 dB
interaural difference will be reduced (to 5 dB, for example), thus providing an
unnatural and less pronounced interaural cue for the listener. However, current
technology allows communication and the sharing of information between the
two HAs, thus ameliorating this potential issue to some degree.
Perception of Pitch and Timbre
Human listeners continuously make perceptual judgments regarding the pitch (perceived on a scale
from low to high) and timbre (a qualitative description of complexity or quality) of sounds in their
auditory environments. From recognizing the sex of a talker (which often relies on voice pitch typically
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associated with fundamental frequency [F0]) to recognizing musical instruments in a musical selection,
these perceptual tasks are completed with minimal effort or attention. For a comprehensive review
of the process of pitch perception and evidence regarding how human listeners perceive pitch, please
review Yost (2009).
Theories of Pitch Perception
There are two generally accepted theories of pitch perception related to tonal stimuli: spectral (place)
and temporal theory. Spectral theory posits that pitch is derived based on place of maximum basilar
membrane excitation for tonal stimuli and multiple locations of basilar membrane excitation for
complex signals. Temporal theory posits that pitch is extracted from the temporal patterns of neural
impulses evoked by the signal. In general, it is accepted that spectral theory allows for the perception
of pitch for high-frequency signals and temporal theory produces pitch sensation for low-frequency
signals due to better phase locking (i.e., the synchronicity of neural firing with the frequency of the
stimulus) of the auditory nerve below 1 kHz (see Figure 3–17 for a visual adapted from Palmer &
Russell, 1986).
Spectral (Place) Theory
Spectral (place) theory of pitch originated in the fact that the auditory system acts as a frequency
analyzer and performs a Fourier analysis (frequency analysis along the basilar membrane) of the
incoming stimulus. The pitch of a signal is thought to be associated with the point at which maximum
basilar membrane displacement occurs.
n
A spectral (place) mechanism is thought to allow for the perception of high-frequency signals
due to an inability of the auditory system to efficiently phase lock to signals above 1 kHz and
a complete inability to phase lock to signals above 5 kHz (Palmer & Russell, 1986). Note
the decrease in synchronization strength (synchronization index) of auditory nerve firing
with increasing frequency in Figure 3–17. As such, because phase locking is poor for highfrequency signals (above approximately 1–5 kHz), the place of auditory excitation provides the
perceptual information to discern signal pitch.
Temporal Theory
Temporal theory of pitch proposes that individual nerve fibers synchronize (fire) to the periodic (phase)
properties of a signal at low frequencies (below approximately 1 kHz). As frequency increases, individual neurons are unable, due to refractory periods and other neural processes, to fire to each phase
of a periodic signal.
n
When this occurs, neighboring frequencies fire at alternating phases, commonly referred to
as the volley principle (Wever & Bray, 1937). This process allows for the encoding of signal
frequency due to a pooled neural response (from which pitch is derived).
Residue Pitch and Case of the Missing F0
While it is the case that F0 plays a role in the perception of pitch, it is also true that pitch can be
preserved in the absence of the F0. Commonly referred to as residue pitch or the case of the missing
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FIGURE 3 –17. Phase locking strength by frequency. Source: Adapted
with the permission of Elsevier, from Palmer, A. R., & Russell, I. J. (1986).
Phase-locking in the cochlear nerve of the guinea-pig and its relation to
the receptor potential of inner hair-cells. Hearing Research, 24(1), 1–15;
permission conveyed through Copyright Clearance Center, Inc.
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fundamental, this phenomenon lends support to the temporal theory of pitch perception as the
removal of frequency component(s), F0 in this case, does not significantly alter the perception of pitch
(although it is possible that the signal may not evoke as strong a sensation of pitch). In this phenomenon, the relative distance between adjacent harmonics in frequencies above F0 creates a periodicity
(pitch period) in the signal associated with F0, and from that, pitch is preserved and extracted.
Q & A
Question: What is a real-world example of residue pitch?
Answer: Historically, the effective bandwidth of most telephones ranged from
approximately 300 to 3400 Hz. As such, spectral energy at F0 for most adult
male and female speakers was outside of the bandwidth of most telephones, and
therefore information at this frequency was not available to listeners. Because the
temporal information (period) associated with F0 is preserved in the signal, the
listener on the other end could determine the sex of the talker (F0 being a salient
cue for talker sex) with little difficulty.
Perception of Timbre
The perception of timbre is a qualitative judgment regarding sound quality or complexity. Timbre is
derived from the spectral envelope of a signal. In other words, two identical harmonic complexes (i.e.,
signal with F0 with subsequent harmonics) with varying harmonic peak energy (e.g., peak energy of
one signal is the second harmonic and peak energy of the other signal is at the sixth harmonic) will have
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similar pitch but will vary in timbre. As such, spectral envelope differences (peak harmonic energy)
among these types of signals provide salient acoustic information for the perception of timbre. Timbre
perception allows listeners to detect two different musical instruments simultaneously playing the same
musical note.
Cochlear Dead Regions and Perceptual Considerations
When cochlear damage becomes severe and involves both the OHCs and inner hair cells (IHCs),
cochlear dead regions occur. A cochlear dead region is a portion of the cochlea void of functioning
OHCs and IHCs. Perceptual consequences of cochlear dead regions commonly include (but are not
limited to):
n
Loss of sensitivity: particularly to low-level sounds, damaged hair cell areas may still be able to
detect sounds at high sound levels due to the vibration of the basilar membrane at frequencies
near the signal frequency (referred to as off-frequency listening). These tonal signals are often
described as having a “scratchy” or noise quality versus a tonal quality.
n
Loudness recruitment: damage to the OHCs resulting in an abnormally rapid growth in loudness,
due to change in slope of the response of the basilar membrane (becoming more linear)
n
Reduction in frequency selectivity: the damaged cochlea results in a reduced ability to
separate or resolve the different frequency components in sounds, leading to poorer frequency
discrimination and speech perception abilities
n
Effects on pitch perception: reduction in the precision of neural phase locking and neural
representation of the temporal fine structure of sounds
AUDIOLOGY NUGGET
The threshold-equalizing noise (TEN) test is a clinical behavioral test for cochlear
dead regions wherein a wideband noise is spectrally shaped to give a constant
masked threshold for a pure tone presented in the noise. The primary purpose of
the TEN test is to determine if the obtained response is representative and being
elicited by the frequency of interest or a result of excitation of a neighboring
frequency (or off-frequency listening). If the frequency of the tone falls within a
dead region, then the threshold will be higher (≥10 dB) with the noise present
(masked) than without (unmasked) and/or the threshold will be at least 10 dB
higher than the presentation level of the TEN. With TEN noise present, the test
tone activity will be masked and the response is actually being elicited from a
neighboring area of the cochlea (which is not masked by the noise). The threshold for the tone will be higher (poorer) than if the tone was detected at the area
of the cochlea tuned to the frequency since the basilar membrane is moving less
at the adjacent areas than the presentation frequency. The presence of a cochlear
dead region has implications for the fitting of amplification, specifically the type
of processing required to account for the dead region (frequency lowering vs.
traditional amplification). For additional details, please refer to Moore (2010).
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n
Effects on speech perception: some parts of speech are inaudible, which decreases ability to
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understand speech; also smears (distorts) spectrum leading to poorer resolution of formants
and other important frequency cues
Instrumentation in Audiology
The provision of audiological diagnostic and rehabilitative services is highly dependent upon the use
of technical equipment. Proper equipment function is determined by standards developed by organizations such as the American National Standards Institute (ANSI) and the International Organization for
Standardization (ISO). Periodically, this equipment requires exhaustive calibration, which is typically
completed by a calibration company with extensive experience in this process. The following sections
include information regarding commonly used instrumentation in audiology service provision but are
not intended to be an exhaustive review.
ANSI and ISO Specifications
Table 3–2 (ANSI) and Table 3–3 (ISO) contain standards relevant to the profession of audiology. ANSI
and the ISO publish a wide range of standards that include determining audiometric zero (0 dB HL)
and the calibration of audiological testing equipment to maximum allowable ambient noise levels for
sound-treated test rooms, among others.
Audiometry Transducers
n
Air-conduction transducers include supra-aural (e.g., TDH-39, TDH-49), circumaural (e.g.,
Sennheiser HDA 200 or 300, Koss HV/1A), insert earphones (e.g., Etymotic ER-3A), and
soundfield speakers. Ultra-high-frequency audiometry (9–20 kHz) is traditionally administered
using Sennheiser HDA 200 or 300 due to a flatter frequency response above 8kHz compared to
supra-aural and insert options, which have significant frequency response roll-off above 8 kHz.
One advantage of insert earphones is higher levels of interaural attenuation than that found
with supra-aural earphones. Interaural attenuation represents the decibel reduction of a
sound as it crosses the head from the test ear to the non–test ear. The average increase in
interaural attenuation is approximately 15 to 30 dB HL (from approximately 40 dB HL
for supra-aural to a conservative 50 to 70 dB HL for inserts if properly inserted). Insert
earphones also protect against collapsing canals common in certain populations (e.g., young
children and elderly individuals).
Using transducers with increased levels of interaural attenuation reduces the need for masking
in cases of asymmetrical hearing loss and instances of masking dilemmas (e.g., significant
bilateral conductive hearing loss), which is helpful in fast-paced clinical environments.
Detailed information on interaural attenuation and masking is provided in Chapter 5.
n
Bone-conduction oscillators deliver a calibrated amount of force to stimulate the bone-
conduction auditory pathway. Theoretically, bone-conduction oscillators can be placed
anywhere on the skull; however, a mastoid or forehead placement is most common.
Interaural attenuation for bone oscillators is conservatively set at 0 dB HL, when in fact it
varies depending upon age and other physical factors.
TABLE 3–2. Relevant ANSI Standards for Audiology
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NUMBER NAME DESCRIPTION
ANSI S3.1-1999 (Revised
2018)
Maximum permissible
ambient noise for audiometric
test rooms
For MPANLs allowed in a test room that
produce negligible masking (2 dB) of
test signals presented at reference level
equivalent threshold levels
ANSI S3.2-1999(R2020) Method for measuring the
intelligibility of speech over
communication systems
For English word lists, methods for
selecting and training the talkers and
listeners, for designing and reporting
test conditions, for calculating the
intelligibility score, for analyzing and
reporting the test results
ANSI S3.6-2018 Specification for audiometers For use in determining the threshold
level in comparison with chosen standard
reference threshold level, including pure
tone, speech, and masking signals
ANSI S3.7-2016 Method for Measurement of
Calibration of Earphones
ANSI S3.13-1987(R2020) Mechanical Coupler for
Measurement of Bone
Vibrators
For use with circum-aural, supra-aural,
and insert-type headphones
For calibrating bone conduction
audiometers and making measurements
on bone vibrations and bone conduction
hearing aids
ANSI S3.20-1995(R2003) Bioacoustical Terminology For definitions for terms including
hearing, speech, psychoacoustics, and
physiological acoustics
ANSI S3.21-2004 Methods for Manual Pure-
Tone Threshold Audiometry
Procedure for pure-tone testing for persons
conducting in industry, schools, medical
settings, and other areas
ANSI S3.25-1989(R2003) Occluded Ear Simulator Designed to stimulate the acoustic portion
of the ear canal between the earmold and
the eardrum, from 100 Hz to 10 kHz
ANSI S3.36-1985(R2006) Specification for Manikin for
Simulated In Situ Airborne
Acoustic Measurements
For various uses including measurement
of hearing aid gain under simulated
conditions and other head-related
transfer functions (HRTFs), and based
on anthropomorphically average adult
manikin head, ear, and torso
ANSI S3.39-1987(R2007) Specification for Instruments
to Measure Aural Acoustic
Impedance and Admittance
For measurements of acoustic impedance,
and acoustic admittance within the ear
canal
(Aural Acoustic Immittance)
ANSI S1.4-1983(R2006) Specification for Sound Level
Meters
For performance specifications for soundmeasuring instruments, including transient
sound signals and digital techniques and
displays
TABLE 3–3. Relevant ISO Standards for Audiology
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NUMBER NAME DESCRIPTION
ISO 8253-1, 2010 Acoustics — Audiometric Test
Methods
— Part 1: Basic Pure
Tone Air and Bone Conduction
Threshold Audiometry
ISO 389-1, 2017 Acoustics
— Reference Zero for
the Calibration of Audiometric
Equipment
— Part 1: Reference
Equivalent Threshold Sound
Pressure Levels for Pure Tones
and Supra-Aural Earphones
ISO 389-2, 1994 Acoustics
— Reference Zero for
the Calibration of Audiometric
Equipment
— Part 2: Reference
Equivalent Threshold Sound
Pressure Levels for Pure Tones
and Insert Earphones
ISO 389-3, 2016 Acoustics
— Reference Zero for
the Calibration of Audiometric
Equipment
— Part 3: Reference
Equivalent Threshold Vibratory
Force Levels for Pure Tones and
Bone Vibrators
Procedures and requirements for
screening purposes only, including air
conduction, pure-tone audiometric test,
speech audiometry, electrophysiological
audiometry, and procedures
A standard reference zero for the scale
of hearing threshold level, for puretone air conduction audiometers, to
promote agreement and uniformity in
the expression of hearing threshold level
measurements throughout the world
Levels supplementary to those specified
in ISO 389:1991 (to be reissued as ISO
389-1), applicable to insert earphones of
type Etymotic Research ER-3A, coupled
to the human ear by ear inserts of type
ER-3-1
Calibration of bone vibrators for pure-tone
bone-conduction audiometry:
(a) reference equivalent threshold vibratory
force levels (RETVFL), for threshold of
hearing of young otologically normal
persons by bone-conduction audiometry;
ISO 389-4, 1994 Acoustics
the Calibration of Audiometric
Equipment — Part 4: Reference
Levels for Narrow-Band
Masking Noise
ISO 389-5, 2006 Acoustics
the Calibration of Audiometric
Equipment — Part 5: Reference
Equivalent Threshold Sound
Pressure Levels for Pure Tones in
the Frequency Range 8 kHz to
16 kHz
— Reference Zero for
— Reference Zero for
(b) essential characteristics of the bone
vibrator and the method of coupling to the
test subject, and to the mechanical coupler
Reference levels for narrow-band masking
noise presented for air conduction in puretone audiometry, in terms of levels to be
added to the reference equivalent threshold
sound pressure levels for the corresponding
pure-tone frequencies
Reference equivalent threshold sound
pressure levels (RETSPLs) of pure tones
in the frequency range from 8 to 16
kHz applicable to the calibration of
air-conduction audiometers for specific
earphones
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