Chapter 4 Powerpoint: Hearing
Warm up
How do we hear?
Audition
 Audition
 the sense of hearing
 Sound
 Sound is the psychological experience that occurs when a change in
air pressure is detected by our outer ear. The frequency and
amplitude of sound waves determine what the sound “sounds like”
 Frequency
 the number of complete wavelengths that pass a point in a given
time
 Pitch
 a tone’s highness or lowness
 depends on frequency
 Decibels (Db)
 How we measure hearing
 Zero decibels is absolute threshold for hearing (arbitrary)
 Every 10 decibels corresponds to 10 fold increase in intensity
The brain transforms sound waves into nerve
impulses that our brain interprets.
• (a) The outer ear funnels sound waves to the
eardrum. The bones of the middle ear amplify and
relay the eardrum’s vibrations through the oval
window into the fluid-filled cochlea. (b) the
resulting pressure changes in the cochlear fluid
cause the basilar membrane to ripple, bending the
hair cells on the surface. Hair cell movements
trigger impulses at the base of the nerve cells,
whose fibers converge to form the auditory nerve,
which sends neural messages to the thalamus and
on to the auditory cortex.
How does the ear work video
Audition- The Ear

Inner Ear
 innermost part of the ear,
containing the cochlea, semicurcular
canals, and vestibular sacs. Carries info to
The brain to be analyzed

Middle Ear
 chamber between eardrum and cochlea
containing three tiny bones (hammer, anvil,
stirrup) that concentrate the vibrations of the
eardrum on the cochlea’s oval window.
Vibrates in response to pressure changes

Outer Ear
 Part of ear where sound waves enter. Made up
of auditory canal and ear drum. Collects
passing changes in air pressure.
Parts of the Ear
Eardrum = tight membrane that vibrates when struck by sound waves.
Bones of the middle ear = the hammer, anvil, stirrup which vibrate with
the eardrum.
Oval window = where the stirrup connects to the cochlea.
Cochlea = a coiled, bony, fluid-filled tube in the inner ear through which
sound waves trigger nerve impulses.
Auditory nerve = nerve which sends the auditory message to the brain
via the thalamus.
The Intensity of Some Common
Sounds

Audition
Place Theory (Helmholtz)
 the theory that links the pitch we hear with the place where the
cochlea’s basilar membrane is stimulated.
 Was found (Bekesy, 1957) that the cochlea vibrates in response to
sound. Vibrations are at different places on the membrane, depending
on the pitch.
 Better explains high pitched sounds b/c low pitch sounds not neatly
localized on basilar membrane
 Frequency Theory
 the theory that the rate of nerve impulses traveling up the auditory
nerve matches the frequency of a tone, thus enabling us to sense its
pitch
 Frequency of neural impulses on auditory nerve translates to pitch
 Problematic because a neuron cannot fire faster than 1000 times/
second but we can sense sounds with frequencies higher than 1000
waves per second! (unless we follow volley principle…. Alternate
firing… some neurons fire while some reload….)
The best theory to explain hearing is probably
a combination of both…
Sound Localization
• Tells us where sound is from
• Stereophonic hearing
• Localization of sounds
– Intensity
– Speed of the sound
• A just-noticeable difference in
direction corresponds to a
time-difference of .000027 sec!
• If sound equidistant from both
ears it is harder to localize
Audition
 Conduction Hearing Loss
 hearing loss caused by damage to the mechanical
system that conducts sound waves to the cochlea
(punctured eardrum/ wax, etc)
 Nerve Hearing Loss (Sensorineural)
 hearing loss caused by damage to the cochlea’s
receptor cells or to the auditory nerve
 Heredity, aging, noise exposure
Cochlear Implant
Electronic device that translates sounds into electrical
signals and sends it to brain
Can correct some sensorineural deafness
Only works if once could hear
Thinking Question:
How is hearing psychological?
Sound Lab
• Answers follow…
5 qualities of sound (psychoacoustics)
• Pitch - (also associated with frequency), the perception of a
high or low sound.
• Loudness - (also called amplitude), the intensity of a sound.
• Phase - the increase and decrease in pressure cycle any
single vibration.
• Direction - (hearing with two ears creates left/right,
high/low, front/back qualities), first come first heard by one
ear or the other.
• Distance - (also associated with reverberation time),
perception of how near or far away a sound's source is.
• Timbre - (also called tone color), the perceived quality of
any sounds' multiple frequencies changing through time.
How does Phone Work
• How the Telephone Works
• When a person speaks into a telephone, the sound waves created
by his voice enter the mouthpiece. An electric current carries the
sound to the telephone of the person he is talking to. A telephone
has two main parts: (1) the transmitter and (2) the receiver.
The Transmitter of a telephone serves as a sensitive "electric ear." It
lies behind the mouthpiece of the phone. Like the human ear, the
transmitter has an 14 eardrum." The eardrum of the telephone is a
thin, round metal disk called a diaphragm. When a person talks into
the telephone, the sound waves strike the diaphragm and make it
vibrate. The diaphragm vibrates at various speeds, depending on
the variations in air pressure caused by the varying tones of the
speaker's voice.
How does record player work
• As you probably know, sound is made up of
vibrations.
The surface of the record is carefully pressed
to make the needle of the record player
vibrate in exactly the right way to recreate the
music. These vibrations are then amplified so
you can hear them.