audition1.ppt visual activity in the eye

Receptors / physiology
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Energy transduction
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First goal of a sensory/perceptual system?
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Transduce environmental energy into neural
energy (or energy that can be interpreted by
perceptual system).
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In hearing, environmental energy = pressure
or sound waves.

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Energy Transduction (cont.)
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Pressure / Sound waves

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Pressure / Sound waves
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When people create a wave, it looks like this:
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When air molecules do, it looks like this:
(Animations courtesy of Dr. Dan Russell, Kettering University)

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Pressure / Sound waves (cont.)
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We can create a graph of pressure at different
locations in space:

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Amplitude (loudness)
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Loudness is measured by how much the air
molecules are compressed after the sound starts,
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while frequency (pitch) is measured by how long
it takes the wave to finish a complete cycle.

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Humans hear tones with frequencies from
20-20,000 Hz. Highest sensitivity in 2000-
5000 range. (Baby cry)
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Most tones aren't pure tones, like those in
previous slides, they're complex tones:

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Anatomy of the ear: outer ear, middle ear, inner
ear

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Anatomy of the ear: outer ear, middle ear, inner ear
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Outer ear
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pinna: part you see; amplifies sounds
around 400 hz; plays a role in sound
localization
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auditory canal: cylindrical tube; conducts
vibrations to eardrum; acts like a horn -
amplifies sound (esp. around 3000 hz)
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eardrum (tympanic membrane): pressure
waves are converted into mechanical
motion

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Middle ear

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Anatomy of the ear: outer ear, middle ear, inner
ear
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Middle ear (cont.)
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ossicles : malleus (hammer), incus (anvil),
stapes (stirrup).
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conduct vibrations from eardrum to oval
window
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more amplification
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muscles attached to the ossicles can retract
reflexively if loud, low frequency sounds are
heard, reducing amplitudes at levels that
might cause hearing damage.

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Middle ear (cont.)
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eustachian tube : ossicles are surrounded by
air; important to keep pressure in middle ear
the same as pressure outside; otherwise
eardrum would stiffen and become less
responsive.
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E. tubes go to throat, open every time we swallow,
equalizing pressure.
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A cold can block tubes, resulting in hearing loss
(usually temporary).
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Infection can be transmitted through E. tubes, esp.
in children, causing fluid buildup - eardrum can
bulge or even burst.

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Middle ear (cont.)
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Bones of the middle ear are necessary
because of the problem of impedance
mismatch. That is, sound doesn't conduct well
between air & water - most sound will be
reflected back.
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Middle ear problems (conduction deafness)
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ear drum punctured
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ear infection - fluid or solid build up in auditory
canal.
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otosclerosis - stiffens stapes so won't function.

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Inner ear

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Inner ear (cont.)
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semicircular canals : Already discussed - used
for determining orientation, not hearing
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oval window 1/15th area of eardrum; helps
increase pressure & deal with impedance
mismatch problem.
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cochlea : snail-shell-like structure; contains
auditory receptors that transduce sound into
neural signals.

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Inner ear (cont.)

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Inner ear (cont.)
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vestibular canal: next to oval window; liquid is
set in motion here; vibrates reissner's
membrane.
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tympanic canal: connected to vestibular canal
via helicotrema (basically a small hole). Vibrates
basilar membrane.
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cochlear duct: separate canal, contains organ of
corti.

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Inner ear (cont.)
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basilar membrane : When pressure is applied to
vestibular & tympanic canals, basilar membrane
becomes distorted - creating a traveling wave

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Inner ear (cont.)
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basilar membrane (cont.)
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Traveling wave
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Because of the traveling wave, the basilar
membrane vibrates differently depending on
tone of sound stimulating it.

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Inner ear (cont.)
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organ of corti : contains hair cell receptors that rest
between basilar membrane & tectorial membrane.
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hair cells : receptors that cause cell to fire when tips are
bent.

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Inner ear (cont.)
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When basilar membrane is displaced, hair cells
are bent by tectorial membrane; when a hair cell
is stimulated, its neuron fires.

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Inner ear (cont.)
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inner ear problems - nerve deafness
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hair cells damaged or broken - can cause tinnitus,
or ringing in the ears, other problems
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cochlear implants - can essentially replace a
cochlea for people who have damage for any
number of reasons. The implant breaks sounds
into component frequencies & then stimulates
auditory nerve, much as cochlea would.

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Inner ear (cont.)
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Bone conduction: alternate way of transmitting
sound to inner ear.
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sounds produce vibration in skull that stimulates
inner ear directly (bypassing middle ear) - usually
only low frequencies.
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ex: chewing on food; dentists drill
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explains why your voice sounds different on tape.

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Brain and auditory cortex
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auditory nerve : carries info from ear to cortex.
Different auditory neurons are sensitive to different
frequency tones; frequency tuning curves:

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Brain and auditory cortex
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Cochlear nucleus: First stop; transmits half info
to same side of brain, and half to opposite side.
(allows binaural processing)
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inferior & superior colliculus : Superior colliculus
involved in integration of vision & audition. I.C.
Has tonotopic organization, meaning neurons
sensitive to similar tones are found near each
other.
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auditory cortex : Still tonotopic, some cells
require more complex stimuli (than mere pure
tones) to become active; clicks, bursts of noise,
etc.

List of terms, section 3
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Transduction
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Pressure/Sound waves
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Amplitude (loudness)
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Compression, rarefaction
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Frequency (pitch)
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Wavelength
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Pure tone, complex tone
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Pinna
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Auditory canal
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Eardrum/tympanic membrane
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Ossicles
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Malleus, Incus, Stapes
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Eustachian tube
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Impedence mismatch
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Otosclerosis
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Oval window
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Vestibular Canal
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Helicotrema
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Cochlear duct
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Organ of Corti
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Basilar membrane
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Traveling wave
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Hair cells
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Tectorial membrane
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Tinnitus
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Nerve deafness/ Conduction deafness
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Cochlear implants
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Bone conduction
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Auditory Nerve
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Frequency tuning curve
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Cochlear nucleus
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Superior/Inferior colliculus
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Auditory cortex
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Tonotopic organization

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