Jon Epp’s Office Hours: Tues 11-12 in EP1246 or by appointment [email protected].

Jon Epp’s Office Hours:

• Tues 11-12 in EP1246 or by appointment

• [email protected]

Sensory Systems: Hearing

What do we hear?

• Sound is a compression wave:

When speaker is stationary, the air is uniformly dense

Speaker Air Molecules

What do we hear?


Speaker

When the speaker moves, it compresses the air in front of it.

What do we hear?


The speaker moves back leaving an area with less air behind - called rarefaction

CompressionRarefaction

What do we hear?


Speaker

The speaker moves forward again starting the next wave

Compression

Rarefaction

What do we hear?

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

Air

Pre

ssur

e

Time

Properties of a Sound Wave

• 1. Amplitude: difference in air pressure between compression and rarefaction


• 1. Amplitude: difference in air pressure between compression and rarefaction– What is the perception that goes along with the

sensation of sound amplitude?


• 1. Amplitude: difference in air pressure between compression and rarefaction– What is the perception that goes along with the

sensation of sound amplitude?

LOUDNESS


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


• 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?


• 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


Ear Drum

Oval window

Sensing Vibrations


Ear Drum

Oval window

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


– amplitude (loudness) - magnitude of displacement of the basilar membrane

–frequency (pitch)

Sensing Vibrations


– amplitude (loudness) - magnitude of displacement of the basilar membrane

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

Sensing Vibrations


–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)


Head accelerates this way

Cupula getspushed

Fluid goes this way


• 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



• People can be knocked down by moving walls!



• 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

Jon Epp’s Office Hours: Tues 11-12 in EP1246 or by appointment [email protected].

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