the mind's machine ch. 6

hearing and balance

auditory world

all around us, increases in density the closer it gets to us

sound waves

perterbations in atmosphere (made of gas, smoke, wator vapor, under pressure) that create pressure waves

wave length/ frequency

measured in Hertz (Hz) and describes pitch

amplitude

measured in decibels (db) and describes loudness

we experience sin waves in multitudes

outer ear

pinna and ear canal. everyone is a little bit different. pinna gathers sound waves and canal funnels them

middle ear

ear drum (tympanic membrane) and ossicles. tympanic membrane gets pushed by air wave, then pushes the ossicles to move. ossicles then hit inner ear (oval window)

inner ear

cochlea (oval window, vestibular and tympanic canal, organ of corti (in medial canal)) and vestibulocochlear nerve. cochlea is filled with water and the oval window is a flexible membrane that when hit moves this water. the circular membrane on other end allows for water to move.

vestibular canal and tympanic canal

have water

middle canal /organ of corti

in between the vestibular and tympanic canal. contains the basilar membrane, tectoral membrane, and the sensory hair cells. basilar membrane is flexible tectoral membrane is rigid

cell’s bases are in basilar membrane and the inner hair cells are not embedded in the tympanic canal and outer hair cells are.

patter of pressure from waves travels in cochlea and reduced space by applying pressure and bends the hair

inner hair cells

one row not embedded, don’t bend just stretch or compress, give us sense of hearing. three rows of hair on each cell, linked via tip links that look like springs so that when one bends they all do. based on which row bends tells nervous system about force and frequency of wave. tip links like a hatch opening, open ion channel allows influx of ions, AP, sent to vetibulocochlear nerve

glutamate and ACh released

outer hair cell

three rows, embedded in tectoral membrane, are bent or pulled with pressure waves, tells us timing of vibration and amplitude of force.

GABA and ACh released

tonotopic organization

the base of the cochlea (where coil starts) hears higher frequency sounds and the apex (center) hears lower frequency. there is an overrepresentation of biologically relevant vibration ranges (the range where the voice falls)

we can hear 20,000hz (20000 oscillations in a second) but we can’t fire 20000 AP in a second

Volley theory: when we get AP that are seperated temporally (wave have to travel down cochlea) we can get info that tells us about perceived pitch

organization of hearing

in brainstem synapses at **cochlear nucleus** and crosses over at the **superior olivary nucleaus.** most info crosses but some stays. then goes up into the **inferior colliculus** in top half of midbrain (toast shaped thing) then up into the **medial geniculate nucleus,** in the thalamus, then sent out into the **auditory cortex,** where sound reaches conscious awareness

place coding

pitch is determined by location of activated hair cells

temporal coding

encodes frequency of auditory stimuli in the firing rate of auditory neurons

biaural cues locate sound source. 2 kinds of cues: intensity difference and latency difference

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intensity difference

difference of loundness. created when ears point different direction and/or if head casts a sound shadow

latency differences

difference of arrival. onset disparity is the disparity b/w when the sound initially reaches ears. ongoing phase disparity is the continued difference in the wave from the onset disparity

spectral filtering

physical structure of ear reinforces some frequencies and diminishes other

latency differences

encoded with interneurons and when the interneurons are activated together

auditory cortex

\-specialized for detecting biologically relevant sound. sensitivity is fine tuned by expeirence during development

\-we have specialization for arbitrary (computer warning, *whoosh* of main, speech) and non-arbitrary (clap, thunder, growl of tiger) sounds

\-we are specialised to hearing our name

herschels gyrus (temporal transverse gyrus)

bigger in musciciens than normal people

amusia

the inability to discern tunes or sing, associated with subtle abnormal function in right frontal lobe and poor connections between frontal and temporal cortex.

for most people it’s really dimusia-tone deafness

outer ear deafness

conduction deafness.

disorders of the outter ear prevent sounds from reaching cochlea. can occur from experience (boxing) or just not having a funnel shape

middle ear deafness

can be from the fusing of the three bones, can’t move anymore

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inner ear deafness

sensorineural deafness- hair cells fail to respond to movement of the basilar membrane, no AP fired

caused by genetic mutation, infections, loud sounds, ototoxic effects of drugs

damage to hair cells can result in tinnitus

deafness in brain

central deafness- damage to auditory brain areas from stroke, tumors, or traumatic brain injury. typically talking about people who are born with normal brain circuitry but something goes awry during life. still receive info just can’t process

word deafness= selective difficulty recognizing normal speech sounds, normal speech and hearing of nonverbal sounds. problems with arbitrary sounds, can hear but can’t recognize meanings

cortical deafness= difficulty recognizing all complex sounds, verbal or nonverbal, rare. wipes out arbitrary and non arbitrary sounds

balance and the vestibular system gen notes

\-set of semicircular canals (the boney labryinth)

\-three fluid filled tubes, each one connects to a utricle and saccule

\-oriented in three planes of head movement

\-head movement initiates flow of fluid in canals, deflects stereocilia in the ampullas, signalling movement in the brain

\-many vetibulocochlear nerve fibers terminate in the vestibular nuclei in brainstem; some project directly to cerebellum

three planes of head movement

nodding (pitch, y-axis)

shaking (yaw, z-axis)

tilting (roll, x-axis)

ampulla

enlarged changer at the base of the canals; contains hair cells embedded in gelatinous flipper that gets pushed either direction based on which way it got pushed. Hair cells report what direction and force it got pushed

kinesthetic sense

utricle and saccule

have specialized receptors that provide acceleration and deceleration signals

otoliths (little rocks)

 a gelatinous plate with hair cells and otoliths. As you move through day, different pressure Is exerted on the otoliths that tell you where you are in relation to ground

motion sickness

results from too much vestibular excitation

sensory conflict theory: we see one thing but feel another and contradictory info it too much

some ppl. thing we evolved naseus to rid the body of ingested toxins that triggered dizziness. the naseua area is geographically very close to where vestibular nerve enter, they might cross talk