Audition
• Anatomy
– outer ear
– middle ear
– inner ear
• Ascending auditory pathway
– tonotopic mapping
• Physical and Psychological qualities of sound
– The complex relationship between the physical and psychological variables
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Audition
• The encoding of pitch
• The encoding of loudness
• The perception of complex tone combinations
– Ohm’s law
– exceptions
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Anatomy
*
* Tympanic membrane
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Anatomy
• Outer ear
– pinna (pinnae) - visible ear
• funnels sound towards ear drum
• helps in sound localization
– external auditory canal
– tympanic membrane
• vibrates to transmit sound wave
• Middle ear
– ossicles - malleus, incus, stapes
• amplifies vibrations
– Eustachian tube
• equalizes pressure
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Anatomy
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Anatomy
• Inner ear - cochlea
– oval window
• sets up waves in the fluid filled cochlea
– helicotrema
• opening between the two outer tubes
– transduction
• basilar membrane
• tectorial membrane
• hair cells
– round window releases pressure of waves
– auditory nerve carries signal to brain
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Anatomy
Tectorial membrane
Hair cells
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Ascending Auditory Pathway
Superior Olivary Nucleus
reflexive localization
Inferior Colliculus
combines auditory with visual
location information
MGN
selective attention
Temporal Lobe
left - language
right - sounds
tonotopic mapping
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Tonotopic Mapping
• Orderly representation of sound in the cortex
– frequencies are represented parallel to the surface
• lower frequencies are represented inferior (lower) than higher
frequencies
– loudness is represented as distance from the surface
• soft sounds are represented near the surface
• louder sounds are represented deeper in cortex
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Tonotopic map of Temporal Lobe
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Sound - Physical Qualities
• Vibration in a medium
• Alternating compressions and rarefactions of pressure
• Physical variations in sound
– frequency
• number of cycles per second (cps)
• often written as Hertz (Hz)
– amplitude
• degree of change in pressure
• measured in decibels (Db)
– complexity
• number of different frequencies present
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Amplitude
Decibels
140
120
110
100
80
60
40
20
0
Sound Example
Rock Band at close range
Loud thunder
Jet Plane from 500 feet
Subway train from 20 feet
Busy street corner
Normal conversation
Typical room noise
Whisper
Threshold for hearing
Note: prolonged exposure to sounds over 85Db produces permanent hearing
loss
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Sound - Psychological Qualities
• Pitch
– varies from low to high
– primarily based on frequency
• Loudness
– varies from soft to loud
– primarily based on amplitude
• Timbre
– based on complexity
– overtones
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Complex Relationships
• Unlike color perception, there is not a simple
relationship between the physical and psychological
variables in audition
• Background
– human range of hearing
• 16 - 16,000 (16K) Hz (or 20 -20K)
• octave = a doubling in frequency
– e.g 20 Hz and 40 Hz are an octave apart, but 1,000 and 2,000 Hz
are also an octave apart
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Complex Relationships
• Pitch is primarily based on frequency
• Two other factors influence perceived pitch
– instructions
– amplitude
• Instructions
– when asked to indicate a change in tone subjects generate the jnd scale
– when asked to indicate a change in musical note they generate the octave
scale
– therefore you need to know the instructions to know what the person will
perceive
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Pitch Scales
7
6
5
4
jnd
3
2
1
0
62
*
125
250
500
1000
2000
4000
8000
16000
Octave scale results in a straight line
* least noticeable change is 0.25 Hz at about 15K, therefore for good recording equipment the
wow and flutter must be less than .25Hz
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Complex Relationships
• Amplitude also influences pitch
– as amplitude increases high tone get higher, low tones get lower, middle
remain the same
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Complex Relationships
• Loudness is primarily based on amplitude
– frequency also influences loudness
• equal loudness contours
• “loudness” control, graphic equalizer
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Equal Loudness Contours
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Encoding Pitch
• Von Bekesy’s Place Theory
– peak of the envelope of the traveling wave is at different locations along the
basilar membrane for different pitches
– high frequency near stapes
– low frequency near helicotrema
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Encoding Pitch
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Encoding Pitch
• Wever’s Volley Theory
– nerves fire in a volley (sequence) to match frequency of pitch
• Both types of encoding are used
– above 5,000 Hz - place theory
– 500 - 5,000 - both (very sensitive)
– below 500 - volley
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Encoding Loudness
• Cells respond to a specific range of firing
– within the range an increase in firing rate
– e.g. a specific set of hair cells might respond to 10-30 Db
• at 10 Db these cells fire slowly, at 20 Db they fire more rapidly, at 30Db
they fire maximally, over 30 Db a new group of cells take over
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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Complex Tone Combinations
• Ohm’s Law
– the ear is a frequency analyzer (Fourier analysis)
– given a complex waveform we hear the component frequencies
• Exceptions to Ohm’s Law
– Harmonics - we hear the multiples as timbre not separate tones
• e.g. if 100 Hz is the fundamental, 200 Hz is the first harmonic and 300
Hz is the second harmonic
• if 225 is the fundamental, the 450 is the first harmonic, and 675 is the
second harmonic
– Beats
• small differences (1-6 Hz) are hear as a waxing and waning of amplitude
Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.
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