INSTRUCTIONAL OBJECTIVES:

1
INSTRUCTIONAL OBJECTIVES
By the end of the class, you will be able
to 1. Describe a critical bandwidth masking
experiment and what it tells us about pitch
perception. 2. State Ohms acoustical law and
discuss how the ear might act as a Fourier
analyzer. 3. Distinguish between conductive and
sensorineural hearing loss in terms of the
location of the damage and the ability to hear
airborne and bone-conducted sound. 4. Define
otitis media, otosclerosis, retrocochlear
dysfunction and presbycusis, and state the type
of hearing loss each condition usually produces.
2
Central auditory pathways
simple tonotopic map in ventral cochlear nuclei
(anterior posterior)
more complex frequency processing in dorsal
cochlear nucleus
Coren et al (2004)
crossed olivocochlear bundles
tonotopic input to inner ear
allow one cochlea to influence the response of
the other
suppresses continuous background noise protects
against damage from loud sounds
3
Central auditory pathways
3 core primary areas receive parallel input from
medial geniculate nucleus
A1
RT
R
all tonotopically organized
RT not well studied yet
Mather (2006)
may provide faster processing
belt areas tonotopic
parabelt areas respond to complex sounds
(speech) modulated by attention
brainstem what where projections to cortex
not worked out
4
Loudness perception
discrimination
typically, a 1 to 2 dB increase in intensity is
required to be able to notice any increase in
loudness, although smaller JNDs have been
reported (pg. 242)
Group 10 - intensity discrimination
5
Pitch perception

• related to frequency of pure tones
• related to fundamental frequency of complex tones

detection frequency range of human hearing is
20-20,000 Hz
6
Pitch perception
discrimination
JND increases as standard frequency increases
pitch discrimination may be worse at higher
frequencies because only place (and not timing)
info is available
7
Pitch perception
masking psychophysical technique measure
absolute threshold for detecting pure tone in the
presence of a noise mask (contains wide range of
frequencies)
2000 Hz test tone
noise mask of varying bandwidth
harder to detect the tone as the noise bandwidth
widens up to a point (the critical bandwidth)
Fig 9.24
e.g. critical bandwidth 400 Hz (frequencies
1800-2200 Hz mask 2000 Hz test tone)
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Pitch perception
bandwidths larger than critical bandwidth contain
frequencies that dont stimulate the same
channel/neuron
critical bandwidth estimates width of frequency
channel used to detect tone
Blake Sekuler (2006)
remember, auditory nerve fibres have a
characteristic frequency and respond to a narrow
range of frequencies
9
Pitch perception
psychophysical tuning curves
signal tone (1 of 6 frequencies black dots)
plus masking tone (varied systematically in
frequency)
Intensity of mask required to keep signal just
detectable
greatest masking occurs when mask and signal have
same frequency
suggests our auditory system has a set of
overlapping channels stretching from low to high
frequencies
10
Pitch perception
Ohms acoustical law separation of sound
components by auditory system based on Fourier
analysis
demo different tones played at the same time
sound like a chord, but the individual sounds can
still be discriminated
ear as Fourier analyzer
www.sinauer.com/wolfe2e/chap9/fourierF.htm
11
Hearing loss
measuring hearing thresholds
audiometer an instrument used to measure
absolute threshold (dB) for pure tones of
different frequencies
12
Hearing loss
audiometry results
use staircase procedure to find absolute
threshold for each frequency
13
Hearing loss
cochlea is stimulated by airborne sounds (eg.
headphones) bone-conducted sounds (eg.
vibration of skull)
What bone-conducted sound do you hear on a
regular basis?
airborne bone-conduction detection thresholds
are measured to assess hearing loss
14
Hearing loss
conductive loss

• problem in outer or middle ear
• disturbance in mechanical transmission of sound
• usually uniform loss at all frequencies
• caused by injured ear drum, infections (otitis
  media), abnormal growth of ossicles
  (otosclerosis)
• can hear bone-conducted but not airborne sound

Coren et al. (2004)
15
Hearing loss
sensorineural loss
damage to cochlea (usually hair cells) or
auditory nerve
Coren et al. (2004)
16
Hearing loss
sensorineural loss

• cochlear damage
• usually restricted to certain frequencies
• caused by infections, genetic disease, otoxic
  drugs, aging, exposure to sudden or prolonged
  loud sound
• cannot hear bone-conducted or airborne sound
• broader frequency tuning

• loudness recruitment abnormally rapid growth of
  loudness as the intensity of sound is increased
  (challenge for hearing aids)

Fig 9.26
17
Hearing loss
sensorineural loss

• presbycusis
• loss begins at high frequencies, but includes
  lower frequencies with advancing age
• wearing out of hair cells with age

• retrocochlear dysfunction
• damage to auditory nerve
• often caused by tumours
• cannot hear bone-conducted or airborne sound