1. PSYCHOACOUSTICS
OF THE PATHOLOGIC
EAR
Ozarks Technical Community College
HIS 110

2. Psychoacoustics and HL
 Recall that acoustics are physical properties of
a sound that are measureable (intensity,
frequency, wavelength)
 Having a hearing loss does not change the
acoustics of sound or the soundwave itself
 Hearing loss changes our psychoacoustic
perceptions of sound

3. Important Terms to Understand
 Dynamic Range (DR)=the range of intensities
from the softest sounds we can hear to the
loudest sounds we can hear
Imagefrom:hearingdirect.com
•In normal-hearing individuals, the
DR of our ears is 140 dB SPL
(from 0-140 dB)
•When we are referring to hearing
loss and the fitting of HAs, the
dynamic range refers to the range
of intensities from the threshold of
hearing (red circles) to the
loudness discomfort level
(“L”=loudest tolerable sound
intensity)
•On the audiogram at right,
the DR at 500 Hz is 80 dB HL
and at 4000 Hz is 55 dB HL

4. Important Terms to Understand
 Linear vs. Non-linear
 Linear refers to an equal input-output system. For
example, in a linear hearing aid, for every
additional 10 dB that comes into the microphone,
the amount of gain or volume coming out of the
speaker is increased by 10 dB.
 Non-linear refers to a system in which the output
of a system in not equal to the amount of input to
the system. For example, in a non-linear hearing
aid, for every additional 10 dB into the
microphone, only an extra 5 dB of gain or volume
may be put out by speaker.

5. Non-Linearity of the Basilar
Membrane
 In NORMAL hearing individuals, the basilar
membrane is NON-LINEAR in the way that it
responds to different sound intensities and
frequencies
 In other words, what comes in is not what comes
out
 If you double the input to the basilar membrane, the
output less than doubles
 If you add a second tone at a different frequency, the
response to the first tone decreases (Two-tone
suppression)
 If you play two tones (say 1000 & 1200 Hz) a third
tone can appear (at 800 Hz) (Cubic Difference Tone)

6. Non-Linearity to Sound
Intensities
 In the cochlea,
specifically, on the
basilar membrane:
 when sound
intensity (dB) is
increased, the
magnitude of the
movement of the
basilar membrane
does not grow
directly in
proportion to that
sound intensity
 If it had a linear
response, the plot
at right would result
in a perfectly- Image from: sciencedirect.com

7. The Purpose of the Cochlea’s Non-
Linearity
 ….to fit the huge range of sound pressures
that our ears are capable of detecting
(dynamic range) into the auditory system

8. Sensorineural Hearing Loss
 Most common type of
hearing loss
 Diagnosed by
elevated air- and
bone-conduction
thresholds (worse
than 20 dBHL) on the
audiogram
 SNHL is usually
associated with
damage to the outer
hair cells of the
cochlea

9. What happens when there is OHC
loss in the cochlea?
 The response of the basilar membrane
becomes more linear
 Loud sounds are not compressed as they once
were
 As a result, loudness recruitment occurs

10. Loudness Recruitment
 Recruitment is an abnormal loudness
perception in individuals with hearing loss
 Oftentimes, patient’s with hearing loss report that
sounds that were once a comfortable volume are
now uncomfortably loud
 Patient’s with SNHL have an elevated threshold
(sound has to be louder for them to hear it);
however, the loudness discomfort level does not
change (it is the same as it was when they had
normal hearing)
 As a result, the rate of loudness growth to their ears is
much more rapid

11. What else happens when there is
OHC loss in the cochlea?
 In a healthy cochlea, the basilar membrane is very
sharply tuned to specific frequencies (i.e. a 2000 Hz
tone results in activation of a very narrow, specific
area on the basilar membrane)
 In cochlear hearing loss, the loss of outer hair cells
results in a broadening of frequency tuning on the
basilar membrane (i.e. a 2000 Hz tone activates a
broader area on the basilar membrane)
 This results in reduced frequency selectivity (usually
occurring in the high frequencies most significantly),
which results in difficulty understanding speech,
especially in noise.

12. SNHL and Timbre
 Timbre is composed of the whole spectrum of
sound—not just the pitch
 Timbre is what allows us to distinguish two
musical instruments, even when they are playing
the same note of identical frequency
 Due to the reduction in frequency selectivity in
SNHL, the ability to hear changes in timbre is
impaired.
 it will be more difficult for the to tell the difference
between different vowel sounds or to distinguish
musical instruments

13. Sound Localization in HL
 Sound localization abilities are reduced with
hearing loss
 Most patients show a reduced ability to use
interaural time and intensity differences
 This is especially true in individuals with asymmetrical
hearing loss
 In addition, people with high-frequency hearing
losses are usually not able to make use of the
directional information provided by the pinna

14. Conductive Hearing Loss
•CHL is due to a problem
with
transmission/conduction
of sound from the outer
ear to the inner ear
•Common causes: wax,
fluid, otosclerosis
•Remember CHL can
often be treated
medically or surgically

15. Psychoacoustics and CHL
 In cases of CHL, the cochlea is healthy
 As a result, patient’s with conductive hearing loss do
not experience distortion of sounds because they still
have normal frequency tuning/selectivity on the
basilar membrane
 As long as sounds are loud enough, they hear clearly
 Patients will report:
 Sounds are softer than normal
 Different tonal quality from normal, depending on the
frequencies affected
 If low frequency CHL, patient’s might say sound is tinny or
Mickey Mouse-like due to mainly hearing high frequency
input
 If high frequency CHL, they might say that sounds are
muffled, mumbly, or have too much bass due to loss of
consonant information