Lecture 10 Sound

1
Lecture 10 - Sound Hearing

• Physics of Sound
• Measuring Loudness
• Functional Anatomy of the Ear
• Auditory Pathways
• Frequency Tuning
• Sound Localization
• Auditory Cortex

2
Sound Hearing

• Physics of Sound
• Measuring Loudness
• Functional Anatomy of the Ear
• Auditory Pathways
• Frequency Tuning
• Sound Localization
• Auditory Cortex

3

• slide 3 - see textbook Fig. 10.2

4
Physics of Sound

• acoustic energy
• mechanical disturbance of air molecules
• air pressure
• tendency of air molecules to move to another
  location
• sound compression rarefaction
• frequency
• amplitude
• phase

5
Sine Wave Characteristics

• slide 5

6

• slide 6 - see textbook Fig. 10.3

7
Physics of Sound

• frequency
• Hz - cycles per second
• (subjective measure pitch)
• pure tones
• sine waves
• complex sounds
• noise
• frequency spectrum

8

• slide 8 - see textbook Fig. 10.5

9
Time Frequency Domain

• slide 9

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12
Complex Sound

• slide 12 G string on violin

13

• slide 13 - see textbook Fig. 10.7

14

• slide 14 - see textbook Fig. 10.8

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Physics of Sound

• sound amplitude
• Pascal, microPascal
• measures air pressure
• decibel (dB) scale
• measures subjective loudness
• phase
• important for localization

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Physics of Sound

• refraction
• reflection
• transmission
• absorption
• speed of sound 340 m/sec
• varies with density of medium

17

• slide 17 - see textbook Fig. 10.1

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Sound Hearing

• Physics of Sound
• Measuring Loudness
• Functional Anatomy of the Ear
• Auditory Pathways
• Frequency Tuning
• Sound Localization
• Auditory Cortex

19
Measuring Loudness - Decibel Scale

• measures subjective loudness in relative terms
• standard reference intensity 0 dB SPL
• 20 microPascals _at_ 1000 Hz
• approximate human threshold
• dB SPL amplitude relative to this standard

20

• slide 20 - see textbook Fig. 10.4

21
Measuring Loudness - Decibel Scale

• think of air pressure differences and perceived
  change in sound intensity
• use dB 20 log (p1/p0)
• e.g. 10-fold increase in pressure 20 dB
• 100-fold increase 40 dB
• 1000-fold increase 60 dB
• etc.

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Sound Hearing

• Physics of Sound
• Measuring Loudness
• Functional Anatomy of the Ear
• Auditory Pathways
• Frequency Tuning
• Sound Localization
• Auditory Cortex

23
Functional Anatomy of the Ear

• outer ear
• directional microphone
• pinna, auditory meatus (canal), tympanic membrane
  (eardrum)

24

• slide 24 - see textbook Fig. 10.9

25
Middle Ear

• slide 25 - see textbook Fig. 10.10

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Functional Anatomy of the Ear

• middle ear
• ossicles malleus (hammer), incus (anvil), stapes
  (stirrup)
• impedance matching
• problem inner ear is filled with fluid -
  reduction in energy of 30 dB
• solution (1) lever action of ossicles (2)
  eardrum is much larger than oval window
• acoustic reflex
• combined response of tensor tympani and stapedius
  muscle
• involuntary reaction reduces movement of stapes
• result reduction in energy by as much as 30 dB

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Functional Anatomy of the Ear

• inner ear
• cochlea
• mechanical vibration of stapes at oval window
  causes pressure oscillation in cochlear fluid
• basilar membrane
• vibrates according to fluid in outer chamber
• lateral inhibition

28
The Cochlea

• slide 28 - see textbook Fig. 10.11

29

• slide 29 - see textbook Fig. 10.12

30
Place Theory

• slide 30 - see textbook Fig. 10.18

31
Place Theory

• slide 31 - see textbook Fig. 10.19

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Traveling Waves

• slide 32 - see textbook Fig. 10.20

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Functional Anatomy of the Ear

• tonotopic organization
• basilar membrane exhibits different pattern of
  vibration for different stimulus frequencies

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Functional Anatomy of the Ear

• organ of Corti
• consists of inner and outer hair cells and the
  tectorial membrane
• difference in vibration between basilar membrane
  and tectorial membrane
• sensory transduction

35
Organ of Corti

• slide 35 - see textbook Fig. 10.13

36

• slide 36 - see textbook Fig. 10.14

37
Sound Hearing

• Physics of Sound
• Measuring Loudness
• Functional Anatomy of the Ear
• Auditory Pathways
• Frequency Tuning
• Sound Localization
• Auditory Cortex

38
Auditory Pathways

• auditory nerve
• from Organ of Corti to Cochlear Nucleus
• spontaneous activity
• frequency tuning
• cochlear nucleus
• first synapse outside the ear

39

• slide 39 - see textbook Fig. 10.22

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Sound Hearing

• Physics of Sound
• Measuring Loudness
• Functional Anatomy of the Ear
• Auditory Pathways
• Frequency Tuning
• Sound Localization
• Auditory Cortex

41
Frequency Tuning

• auditory nerve fibers
• characteristic frequency

42

• slide 42 - see textbook Fig. 10.24

43

• slide 43 - see textbook Fig. 10.25

44

• slide 44 - see textbook Fig. 10.23

45

• slide 45 - see textbook Fig. 10.26

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Sound Hearing

• Physics of Sound
• Measuring Loudness
• Functional Anatomy of the Ear
• Auditory Pathways
• Frequency Tuning
• Sound Localization
• Auditory Cortex

47
Sound Localization

• localization problem
• mismatch between proximal and distal info.
• no direct encoding of spatial relationships
• solution
• binaural processing
• IID - inter-aural intensity differences
• ITD - inter-aural time differences
• time delay circuit
• auditory receptive field

48

• slide 48 - see textbook Fig. 10.27

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Sound Hearing

• Physics of Sound
• Measuring Loudness
• Functional Anatomy of the Ear
• Auditory Pathways
• Frequency Tuning
• Sound Localization
• Auditory Cortex

50
Auditory Cortex

• tonotopic organization
• cortical magnification
• for frequencies carrying speech sounds

51
Auditory Cortex
52

• slide 52 - see textbook Fig. 10.22

53

• slide 53 - see textbook Fig. 10.21