Audition: Sound, the Ear,

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Audition Sound, the Ear, the BrainPsyc 351
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Functional Utility of Sound

• Carries information helpful for locating where
  things are, where you are (outside, in a large
  room, on firm ground, etc.)
• Carries information good for identification (we
  can identify friends from their footfalls)
• Travels well in air (not that quickly, and with
  echoes and reflections, but overall does well)

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The nature of sound

• Pressure waves compression and rarefaction
• Sine waves
• Three dimensions of sound
• Amplitude
• Frequency
• Phase
• Speed of sound 1100 feet/sec in air (x 5
  faster in water)

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Amplitude, Frequency, Phase
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The nature of sound
Pressure wavesSine waves Three dimensions
Amplitude Frequency Phase
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Sounds in the natural environment
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Fourier analysis
Fourier Analysis analyzing complex waves into
simpler components sine waves Fourier
Synthesis the reverse adding sine waves to
create complex waves
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Fourier analysis
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Fourier Synthesis
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Representations amplitude waveforms vs.
spectrographs
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Amplitude The Decibel scale

• A ratio scale
• referenced to the classical threshold of human
  hearing, nominally .0002 dynes/cm2
• (Factoid dyne force needed to accelerate 1g
  to 1cm/sec in 1 sec
• A logarithmic scale
• converts multiplicative changes to additive
  changes
• Thus, db 20 x log (P1/P0) in sound pressure
  level, where P0 .0002 dynes/cm2

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Amplitude Range
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Frequency cycles/sec, or Hertz(Hz, from German
physicist Heinrich Hertz)

• Middle C on piano 261.6 Hz
• http//en.wikipedia.org/wiki/Piano_key_frequencies
  

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Frequency
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Frequency Range for Human HearingNominally 20
20KHz
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Normal vs. Impaired Hearing
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Comparative Hearing
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Phase

• The relative positions/timing of two waves
  matched for db, Hz

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Phase

• Three binaural cues to the direction from which a
  sound is coming
• Phase difference between left and right ear
• Time of arrival difference
• Intensity different (head creates an auditory
  shadow)
• Monaurally, humans appear to be phase-deaf.

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The Ear versus the Eye

• Orientation
• Attention
• Speed
• Sensitivity
• Echoes
• Eye 400 700 nm, trichromaticity
• Ear 20-20k Hz. Tri- tonaticity? No

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Structure of the ear

• Outer structures (pinna)
• Inner structures
• Auditory canal
• Tympanic membrane, acoustic reflex
• Ossicles Malleus, Incus, Stapes
• Oval window
• Cochlea, basilar membrane, Organ of Corti
• Cilia inner vs. outer hair cells
• Mechanism of transduction
• Impedance matching 30 db loss

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The Ear, starting from the outside
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The Ear in cross-section
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The Ear in cross-section
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MiddleEar
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Dynamics of the middle ear

• http//funsan.biomed.mcgill.ca/funnell/OpenHouse9
  6/me_anim.html

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The Cochlea
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BasilarMembrane
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Hair Cells, outer and inner
Also http//mysite.du.edu/kinnamon/3640/hearing/h
earing.html
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Mouse Organ of Corti(courtesy of Audrey Nath and
Jeff Triffo)
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BrainPathwaysforaudition
Cochlear nucleus Superior Olive Inferior
colliculus Medial geniculate Auditory Cortex
(A1)
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Auditory Tuning Curves
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More Auditory Tuning Curves
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Tonotopic Map ofMonkey Auditory Cortex
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Inner EarSummary
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Coding mechanisms

• Place theory coding frequency and amplitude
• Volley principle large numbers of detectors
• Periodicity coding frequency and amplitude
• Duplicity theory 1 KHz to 4 KHz
• Missing fundamental, masking

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Pathways and Brain Mechanisms

• Cochlear nucleus
• Superior olive
• Inferior colliculus
• Medial geniculate
• Auditory cortex
• Tonotopic mapping
• Tuning curves for "tone detectors"
• Detectors tone, onset/offset, sweep

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• Psychophysics
• Basic audiogram (repeat from earlier in semester)
• Masking, critical band