Jon Epp’s Office Hours:
• Tues 11-12 in EP1246 or by appointment
• jon.epp@uleth.ca
Sensory Systems: Hearing
What do we hear?
• Sound is a compression wave:
Speaker
Air Molecules
When speaker is stationary, the air is
uniformly dense
What do we hear?
• Sound is a compression wave:
Speaker
When the speaker moves, it compresses the air in front of it.
What do we hear?
• Sound is a compression wave:
Rarefaction
Compression
The speaker moves back leaving an area with less air behind called rarefaction
What do we hear?
• Sound is a compression wave:
Speaker
Compression
Rarefaction
The speaker moves forward again starting the next wave
What do we hear?
• Sound is a compression wave - it only “looks”
like a wave if we plot air pressure against time
Time
Properties of a Sound Wave
• 1. Amplitude: difference in air pressure
between compression and rarefaction
Properties of a Sound Wave
• 1. Amplitude: difference in air pressure
between compression and rarefaction
– What is the perception that goes along with the
sensation of sound amplitude?
Properties of a Sound Wave
• 1. Amplitude: difference in air pressure
between compression and rarefaction
– What is the perception that goes along with the
sensation of sound amplitude?
LOUDNESS
Properties of a Sound Wave
• 2. Frequency: how many regions of
compression (or rarefaction) pass by a given
point per second (expressed in Hertz)
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?
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
Sensing Vibrations
Sensing Vibrations
• Outer ear transmits
and modifies
sound (critical for
sound localization)
Sensing Vibrations
• Middle ear turns compression waves into
mechanical motion
oval window
stapes
Sensing Vibrations
• Middle ear turns compression waves into
mechanical motion
Oval window
Ear Drum
Sensing Vibrations
• Middle ear turns compression waves into
mechanical motion
Oval window
Ear Drum
Compression Wave
Sensing Vibrations
• The cochlea, in the inner ear, is a curled up
tube filled with fluid.
Auditory
Nerve to
Brain
Sensing Vibrations
• Inside cochlea is the basilar membrane
• Movement of the oval window causes
ripples on the basilar membrane
Sensing Vibrations
• Basilar membrane measures the amplitude
and frequency of sound waves
– amplitude (loudness)
–frequency (pitch)
Sensing Vibrations
• Basilar membrane measures the amplitude
and frequency of sound waves
– amplitude (loudness) - magnitude of
displacement of the basilar membrane
–frequency (pitch)
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
Sensing Vibrations
• Basilar membrane measures the amplitude
and frequency of sound waves
–frequency (pitch) - frequency and location of
displacements of the basilar membrane
Sensing Vibrations
• Bundles of “hair cells” are embedded in
basilar membrane
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
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!
How Can You Localize Sound?
• 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. That’s what your auditory system
does!
How do we Stay Balanced?
The Vestibular System
Vestibular System (Balance)
Vestibular System (Balance)
Vestibular System (Balance)
Vestibular System (Balance)
Head
accelerates
this way
Fluid goes
this way
Cupula gets
pushed
Vestibular System (Balance)
Fluid goes
this way
Head
accelerates
this way
Cupula gets
pushed
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!
Vestibular, Visual, and Proprioceptive
Systems Work Together
• Try standing on one foot with your eyes closed!
Fun Facts about The Vestibular
System
• Seasickness arises when the vestibular system and
the visual system send conflicting information
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!
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
Next Time: Taste, Smell, Touch