Sensory Systems: Auditory

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Sensory Systems Auditory
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What do we hear?

• Sound is a compression wave

Speaker
Air Molecules
When speaker is stationary, the air is uniformly
dense
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What do we hear?

• Sound is a compression wave

Speaker
When the speaker moves, it compresses the air in
front of it.
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What do we hear?

• Sound is a compression wave

Rarefaction
Compression
The speaker moves back leaving an area with less
air behind - called rarefaction
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What do we hear?

• Sound is a compression wave

Compression
Speaker
Rarefaction
The speaker moves forward again starting the next
wave
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What do we hear?

• Sound is a compression wave - it only looks
  like a wave if we plot air pressure against time

Air Pressure
Time
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Properties of a Sound Wave

• 1. Amplitude difference in air pressure between
  compression and rarefaction (Sound Pressure
  Level)

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Properties of a Sound Wave

• 1. Amplitude difference in air pressure between
  compression and rarefaction (Sound Pressure
  Level)
• What is the perception that goes along with the
  sensation of sound amplitude?

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Properties of a Sound Wave

• 1. Amplitude difference in air pressure between
  compression and rarefaction (Sound Pressure
  Level)
• What is the perception that goes along with the
  sensation of sound amplitude?

LOUDNESS
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Properties of a Sound Wave

• 2. Frequency how many regions of compression
  (or rarefaction) pass by a given point per second
  (expressed in Hertz)

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Properties of a Sound Wave

• 2. Frequency how many regions of compression
  (or rarefaction) pass by a given point per second
  (expressed in Hertz)
• What is the perception that goes along with the
  sensation of frequency?

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Properties of a Sound Wave

• 2. Frequency how many regions of compression
  (or rarefaction) pass by a given point per second
  (expressed in Hertz)
• What is the perception that goes along with the
  sensation of frequency?

PITCH
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Sensing Vibrations
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Sensing Vibrations

• Outer ear transmits and modifies sound (critical
  for sound localization)

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Sensing Vibrations

• Middle ear turns compression waves into
  mechanical motion

oval window
stapes
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Sensing Vibrations

• Middle ear turns compression waves into
  mechanical motion

Oval window
Ear Drum
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Sensing Vibrations

• Middle ear turns compression waves into
  mechanical motion

Oval window
Ear Drum
Compression Wave
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Sensing Vibrations

• The cochlea, in the inner ear, is a curled up
  tube filled with fluid.

Auditory Nerve to Brain
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Sensing Vibrations

• Inside the cochlea is the basilar membrane
• Movement of the oval window causes ripples on the
  basilar membrane

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Sensing Vibrations

• Basilar membrane measures the amplitude and
  frequency of sound waves
• amplitude (loudness)

• frequency (pitch)

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Sensing Vibrations

• Basilar membrane measures the amplitude and
  frequency of sound waves
• amplitude (loudness) - magnitude of displacement
  of the basilar membrane

• frequency (pitch)

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Sensing Vibrations

• Basilar membrane measures the amplitude and
  frequency of sound waves
• amplitude (loudness) - magnitude of displacement
  of the basilar membrane

• frequency (pitch) - frequency and location of
  displacements of the basilar membrane

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Sensing Vibrations

• Basilar membrane measures the amplitude and
  frequency of sound waves

• frequency (pitch) - frequency and location of
  displacements of the basilar membrane

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Sensing Vibrations

• Bundles of hair cells are embedded in basilar
  membrane

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Sensing Vibrations

• When hair cells sway back and forth, they let
  ions inside
• This flow of charges is converted to action
  potentials and sent along the auditory pathway

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The Auditory Pathway

• The auditory pathway is complex and involves
  several stations along the way to the auditory
  cortex in the brain
• Lots of processing must be done in real-time on
  auditory signals!

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How Can You Localize Sound?

• Ponder this
• Imagine digging two trenches in the sand beside a
  lake so that water can flow into them. Now
  imagine hanging a piece of cloth in the water in
  each trench. Your job is to determine the number
  and location and type of every fish, duck,
  person, boat, etc. simply by examining the motion
  of the cloth. Thats what your auditory system
  does!

- Al Bregman
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How do we Stay Balanced?

• The Vestibular System

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Vestibular System (Balance)
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Vestibular System (Balance)
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Vestibular System (Balance)
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Vestibular System (Balance)
Head accelerates this way
Fluid goes this way
Cupula gets pushed
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Vestibular System (Balance)
Fluid goes this way
Head accelerates this way
Cupula gets pushed
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Vestibular System (Balance)

• movement of the cupula is detected by hair cells
• hair cells in the vestibular system are more
  sensitive than hair cells on the basilar membrane!

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Vestibular, Visual, and Proprioceptive Systems
Work Together

• Try standing on one foot with your eyes closed!

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Fun Facts about The Vestibular System

• Seasickness arises when the vestibular system and
  the visual system send conflicting information

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Fun Facts about The Vestibular System

• Seasickness arises when the vestibular system and
  the visual system send conflicting information
• People can be knocked down by moving walls!

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Fun Facts about The Vestibular System

• Seasickness arises when the vestibular system and
  the visual system send conflicting information
• People can be knocked down by moving walls!
• Alcohol causes the spins by (among other things)
  changing the density of the fluid in the
  semicircular canals

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Hearing

• Detection
• Loudness
• Localization
• Music
• Speech

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Detection and Loudness

• Sound level is measured in decibels (dB) - a
  measure of the amplitude of air pressure
  fluctuations

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Detection and Loudness

• Sound level is measured in decibels (dB) - a
  measure of the amplitude of air pressure
  fluctuations
• dB is a log scale - 1 dB difference 10 times
  the actual air pressure

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Detection and Loudness

• Sound level is measured in decibels (dB) - a
  measure of the amplitude of air pressure
  fluctuations
• dB is a log scale - 1 dB difference 10 times
  the actual air pressure
• We have a dynamic range that is a factor of 7.5
  million!

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Detection and Loudness

• minimum sound level necessary to be heard is the
  detection threshold

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Detection and Loudness

• detection threshold depends on frequency of
  sound
• very high and very low frequencies must have more
  energy (higher dB) to be heard
• greatest sensitivity (lowest detection threshold)
  is between 1000 hz to 5000hz

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Detection and Loudness

• Detection can be compromised by a masking sound
• even masking sounds that are not simultaneous
  with the target can cause masking (forward and
  backward masking)