Download Auditory

Sensation and Perception
In this part of the course we will
try to answer such questions as:
How do we see and hear?
Why does a TV only need three
phosphors (Red, Green and Blue) to
allow us to see all colors?
Why are some sounds easier to
hear than others?
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Sensation
Sensation - the registration of
physical stimuli
Hearing - anatomy and function of the
ear
Vision - anatomy and function of the
eye
Psychophysics - the measurement of
sensory experiences
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Sensation
What is the purpose of sensory
processing?
To transform physical stimuli in the
environment into neural signals in the
brain
Example (Hearing): Sound waves are
transformed into vibrations in the ear,
and the strength of those vibrations
are coded by sensory neurons
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Three Domains of Sensory
Research
Sensory Physiology
Physiological Psychology
Psychophysics
Physiological response
Domain of
Sensory physiology
Physical stimulus
Domain of sensory
physiological psychology
Sensory experience
Domain of sensory psychophysics
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Hearing: Sound Waves
Auditory perception occurs when
sound waves interact with the
structures of the ear.
Sound Wave - changes over time in the
pressure of an elastic medium (for
example, air or water).
Without air (or another elastic medium)
there can be no sound waves, and thus
no sound
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Characteristics of Sound
Least compression
 Frequency of a
Greatest compression of molecules
of molecules
sound wave is
related the
pitch of a
sound
One cycle
Amplitude
 Amplitude of a
sound wave is
(a)
Higher frequency
Lower frequency
related to
(Higher pitch)
(Lower pitch)
loudness of a Higher
amplitude
sound
(Louder)
Lower
amplitude
(Softer)
(b)
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Frequency of Sound Waves
The frequency of a sound wave is
measured as the number of cycles per
second (Hertz)
20,000
 4,186
 1,000

100

27
Hz
Hz
Hz
Hz
Hz
Highest Frequency we can hear
Highest note on a piano
Highest pitch of human voice
Lowest pitch of human voice
Lowest note on a piano
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Intensity of Various Sounds
Example
Softest detectable sound
P (in soundpressure units) Log P Decibels
1
0
0
10
1
20
100
2
40
1000
3
60
Loud music from a radio
10,000
4
80
Heavy automobile traffic
100,000
5
100
1,000,000
6
120
10,000,000
7
140
100,000,000
8
160
1,000,000,000
9
180
Soft whisper
Quiet neighborhood
Average conversation
Very loud thunder
Jet airplane taking off
Loudest rock band on record
Spacecraft launch 9from 150 ft.)
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Intensity of Sound Waves
The physical intensity of sound waves
is measured on the decibel (dB) scale
Intensity (in dB) = 20 log (P/P0)
P = intensity of sound being measured
P0 = the lowest intensity 1,000 Hz tone we
can hear
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Anatomy of Ear
Purpose of the structures in
the ear:
Measure the frequency (pitch)
of sound waves
Measure the amplitude
(loudness) of sound waves
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Major Structures of the Ear
Outer Ear - acts as a funnel to direct
sound waves towards inner structures
Middle Ear - consists of three small
bones (or ossicles) that amplify the
sound
Inner Ear - contains the structures that
actually transduce sound into neural
response
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Anatomy of the Ear
Pinna
Semicircular
Stirrup canals
Hammer
Anvil
Bone
Auditory
nerve
Sound
waves
Cochlea
Auditory
Canal-
Eardrum
(tympanic
Membrane)
Round
window
Oval window
Where stirrup
attaches
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Anatomy of the Ear
Outer ear Middle ear
Inner ear
Cochlea,
partially
uncoiled
Tectorial
membrane
Hair cells
Hammer Anvil
Basilar
membrane
Stirrup
Oval window
Sound
waves
Auditory
canal
Eardrum
Round window
A sound causes
the basilar
membrane to wave
up and down.
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Transduction of Sounds
The structures of the ear transform
changes in air pressure (sound waves)
into vibrations of the Basilar Membrane.
As the Basilar Membrane vibrates it
causes the hairs in the Hair Cells to
bend.
The bending of the hairs leads to a
change in the electrical potential within
the cell
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Coding of Sounds
The pattern of vibration along the Basilar Membrane
depends on the Frequency of the sound wave
Oval window
Direction of traveling wave
Proximal
end
Distal
end
Basilar
membrane
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Coding Sounds
 Low frequency
sounds cause more
vibration near
distal of Basilar
Membrane
 High frequency
sounds cause more
vibration near
proximal end of
Basilar Membrane
Vibration
amplitude
of basilar
membrane
Bassoon, loud
Piccolo, soft
Distance along basilar membrane
(a)
Effect of bassoon on basilar membrane
Vibration
amplitude
of basilar
membrane
Piccolo, loud
Bassoon, soft
Distance along basilar membrane
(b)
Effect of piccolo on basilar membrane
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Coding and Auditory Masking
The way in which waves travel
down the Basilar Membrane
causes some sounds to interfere
with (or mask) our ability to hear
other sounds
Low frequency sounds provide
better masking than high
frequency sounds.
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Auditory Masking
 Low frequency
sounds effectively
mask high
frequency sounds
 High frequency
sounds can not
effectively mask
low frequency
sounds
Vibration
amplitude
of basilar
membrane
Bassoon, loud
Piccolo, soft
Distance along basilar membrane
(a)
Effect of bassoon on basilar membrane
Vibration
amplitude
of basilar
membrane
Piccolo, loud
Bassoon, soft
Distance along basilar membrane
(b)
Effect of piccolo on basilar membrane
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