Perception: The Auditory System: Sound And The Ear

Front 1

Bell Jar Experiment

Back 1

Robert Boyle 1660 - showed how a bell becomes silent if the air is pumped out of a jar. this form of energy loss is called damping

Front 2

Inertia and elasticity

Back 2

properties an object must posses in order to vibrate: resisting being moved vs resisting rest. Greater the mass greater the inertia. the interaction of these two opposing forces results in vibration

Front 3

simple harmonic motion

Back 3

the back and forth movement of the prongs of a tuning fork over time from one extremity to the other which occurs in a smoothly varying manner

Front 4

compression vs refraction

Back 4

air molecules surrounding an object become crowded resulting in momentary increase in air pressure vs when air molecules thin out causing a momentary decrease in air pressure. Both of these create alternating air pressure fluctuations which radiate outward from an object (like the tuning fork) in a spherical pattern to produce a 'traveling wave' (see image 'the impact of the tuning fork')

Front 5

sinusoidal movement

Back 5

a smoothly varying back and forth movement that is described by a sine curve. this results in a PURE TONE (rare in environmental sounds but common in human vocalizations and instruments)

Front 6

intensity, amplitude

Back 6

a term describing the physical characteristics of sound in terms of their loudness, expressed on a logarithmic scale;the height of the waves

Front 7

Bel scale; problem with it? SPL?

Back 7

a scale of the logs of intensity ratios. the problem with this is that log transformations produce compressions which are too excessive because the scale is so small that minor changes in intensity would be hard to relate on bel scale. To solve this, we convert the scale to decibels dB (one tenth of a bell). We attach SPL sound pressure Level to show that our reference is the minimum humans can hear. Thus, dBspl= 10 log (Is/Ir)

Front 8

frequency (3); Resonant frequency

Back 8

-the number of complete cycles (one instance of compression and one of refraction) per second, measured in hertz .
-The frequency of a particular tuning fork will stay the same no matter how hard or soft you tap it.
-we can hear 20-20000 hertz

-the natural vibrational frequency of an object specified by its combination of mass and stiffness. to create a fork with a higher frequency we must decrease its mass or increase stiffness. example in class= tacoma narrows bridge

Front 9

what is the speed of sound? how dos sound relate to temp and elasticity?

Back 9

331.5 m/s.
-as temp increases the speed of sound increases because density decreases. every 1 degree C increase in temp is a .6m/s increase in speed
- as elasticity of the medium increases, sound speed increases

Front 10

regular periodic sounds? complex periodic sounds? (3)

Back 10

regular periodic sounds -the pattern of pressure change repeats itself at regular intervals;
complex-a repeating wave that does not have a sinusoidal profile
- complex sounds evoke a sense of highnesss/lowness called pitch
- complex sounds can be constructed form combinations of pure sounds

Front 11

complex aperiodic sounds; white noise

Back 11

vibrations appear to be random in nature. aka noise. can be created by combining a large set of random frequencies with random amptitudes. UNPREDICTABLE. If the pattern is composed of all frequencies in a range, like human range, it is called white noise- roar of traffic, fan

Front 12

Fourier analysis; Fourier Spectrum

Back 12

the idea that any function (periodic or aperiodic) can be broken down into a series of sine and cosine waves (so any complex waveform can be broken into a series of patterns without any knowledge of what those constituent patterns are; a plot representing the information from Fouriers Analysis in terms of amplitude and frequency.

Front 13

Ohm's Law of hearing

Back 13

Ear functions as a Fourier analyzer that decomposes complex sounds. shown to be wrong!

Front 14

What two things affect sound transmission?

Back 14

intensity becomes dissipated with distance
and sound wave must interact with objects in their path

Front 15

Inverse Square Law

Back 15

sound intensity is inversely related to the square of the distance from the sound source. for example, 3(distance) means a one-third reduction in intensity

Front 16

Absorption Coefficient

Back 16

the proportion of sound energy absorbed against the energy contained in the wave. in other words, how much a medium allows a sound (or light ) to penetrate it. Water has a relatively low coefficient.

Front 17

Diffraction

Back 17

This occurs when a wave encounters an object that is too small for reflection or absorption and so the waves bend around the object. sound waves of high frequency cannot be diffracted as easily .

Front 18

What are three ways a sound wave can interact with an object in its path? what is acoustic impedance?

Back 18

reflecion, absorption, diffraction; the resistance of a medium to sound transmission

Front 19

Reverberation Time

Back 19

Wallace Sabine noted that the most important factor in acoustic suitability is the sound reflection, somehting he quantified as reverberation time

Front 20

Pinna; eustachian tube

Back 20

- tunnel that funnels sound to ear drum, slightly s-shaped, 25 mm in length and 5-7 mm n diameter
connects middle ear to back of throat to ensure that the vibrational properties of the eardrum are less significantly affected by the outside air pressure

Front 21

What three ways can sound waves arriving at the eardrum be transferred through the middle ear?

Back 21

1) through the bony matrix of the head 2) conducted through air present in the middle ear 3) vibrating off the ossicles (malleus, incus, stapes)

Front 22

Oval Window

Back 22

sound travels through the Ossicles, and the stapes connects to the oval window where the sound is transferred to the inner ear

Front 23

Cochlea; 3 channels

Back 23

- fluid filled structure that contains the sensory transduction apparatus
-divided into three channels: the scala Vestibuli, scala media, scala tampani

Front 24

Reissner's Membrane, Basilar Membrane

Back 24

separates cochlear duct from scala vestibuli; separates cochlear duct form scala tympani

Front 25

Describe how sound goes from wave to biochemical signal

Back 25

funneled through the pinna to the tempanic membrane, through the ossicles, to the oval window and into the cochlea. the back and forth movement of the stapes sets off compression waves in the cochlear fluid of the scala vestibuli. The pressure created by inward movement of stapes on oval window is sent through the scala vestibuli and across the Reissners membrane, through the cochlear duct and across the basilar membrane into the scala tympani. must maintain loyalty to original amplitude and frequency. the mechanical stimulation of the basilar membrane stimulates movement in the organ of corti. This causes the basilar and tectorial membranes to rub alternating, bending the stereocillia and tensioning the tip links, opening ion channels, which causes a depolarization and neurotransmitter release at the nerve cells

Front 26

How is Amplitude Preserved as sound moves throughout ear? (4) How much pressure loss would we otherwise see?

Back 26

There would be approx a 30dB pressure loss if not for:
-the lever effect-as sound is transferred from malleus to incus because of the size difference there is a small increment in mechanical force
-the condensation effect: the surface of the tympanic membrane is 20 times that of the the footplate of the stapes and as the sound condenses form a large to small area, we see amplification
- The resonance effect: due to resonant properties, sounds of 2500 Hz are boosted as they go down the canal, and 4000 to 5000 Hz are boosted as they travel down the pinna
- The directional effect: The ossicles chain channels all sound onto oval window which causes reciprocal movement of oval window

Front 27

What are the 3 theories for how Frequency is Preserved as sound moves throughout ear? (3)

Back 27

the resonance theory- basilar membrae composed of fibres tunes to different frequencies
the frequency theory- auditory nerve fibres are stimulated by the basilar membrane and it is their firing that conveys frequency. PROBLEMS:neurons fire all-or-none, and basilar membrane is not consistent in dimensions
the place theory- sounds of different frequencies produce a pattern whose maximum amplitude occurs at different places along the basilar membrane. Fluid movement in basilar membrane induces a travelling wave

Front 28

Tonotopic Map

Back 28

the upper frequency of hearing is represented at base of basilar membrane whereas the lower limit is at the apex (wider end). The physical properties of the basilar membrane provide an effective means of encoding and representing complex sounds. low frequency info reaches brain slower

Front 29

Hair cells

Back 29

-inner- humans have 3,000-3,500, on inner arch of corti
-outer- 12,000- attached to basilar membrane, protrude into tectorial membrane
-both contain stereocilia but only those of the outer cells are connected to the tectorial membrane in the organ of corti

Front 30

tip links

Back 30

filaments connecting inner hair cells sterocillia together. Upward movement of basilar membrane causes rightward bending of the stereocilla, which increases tension on tip links and ion channels open, which depolarizes membrane and leads to neurotransmitter release

Front 31

Roles of outer hair cells

Back 31

- influence strength of shearing force on stereocilla of inner hair cells through mechanical responses (when mechanically stimulated, they can contract or expand to influence the tectorial membrane) and electrical responses (cochlear microphonic)

Front 32

cochlear microphonic; otoacoustic emissions

Back 32

the electrical response across the organ of corti produced from movement of outer hair cells in response to basilar membrane. this enhances the electrical response of the inner hair cells; sounds generated when outer hair cells change length

Front 33

Vestibulocochlear Nerve (8th nerve)/Cochlear Nerve (3)

Back 33

-8th nerve has two components- the vestibular branch that innervates the the vestibular apparatus and the cochlear nerve
-each cochlea is innervated by 30,000 nerve fibres
-these fibres are responsible for treating frequency and intensity info to the CNS

Front 34

Spiral Ganglion

Back 34

-the fibres of the cochlear nerve originate form the cochlear ganglion found outisde the cochlea called the 'spiral ganglion' because it follows the spiral of cochlea
- approximately 90% of cochlear nerve fibres terminate upon inner hair cells

Front 35

Each cochlea afferent fibre terminates upon one INNER hair cell (efferent terminate on OUTER). the 3,000 hair cells stimulate the 30,000 afferent fibres because each hair cell, can direct its output through about 10 fibres. What is the benefit of these multiple projections?

Back 35

differences in processing can occur at each of the synapses by controlling how much neurotransmitter is released there. this allows stimulus to be separately represented in subtle ways

Front 36

tuning curve; characteristic frequency

Back 36

a plot of the minimum sound intensity required to obtain a sufficient neural response as a function of sound frequency; the frequency at which the neuron has the highest sensitivity

Front 37

frequency response curve

Back 37

FRCs portray essentially the same information with regard to frequency selectivity as the tuning curve but because the dependent measure is neural discharge, it is possible to show frequency response at different sound levels as well.

Front 38

what do the frequency response and tuning curves show?

Back 38

that auditory fibres in the cochlear nerve are narrowly tuned to a particular frequency. The basilar membrane is responsible for this.

Front 39

phase- locked response

Back 39

an action potential may be produced during each cycle of the sound wave, and neural discharge occurs in the stereotyped way. This response persisits up to frequencies of 4000 Hz

Front 40

describe the ascending pathways to the auditory cortex (4)

Back 40

1)begins at neurotrans release by hair cells to cochlear nerve cells, which give way to the spiral ganglion and then the Vestibulocochlear Nerve, which enters brain stem and terminates at cochlear nucleus.
2) cochlear nucleus has two main subdivisions: one with relay cells and one with cells involved in enhancing and sharpening signals- there is no crossover at this level (cochlear nucleus cells are Monaural)
3) from cochlear nucleus, projections go to superior olive and inferior colliculus. Projections may be directed to same side of brain as well as opposite, meaning the cells here are binaural
4) the superior olive projects to inferior colliculus which projects to the MGN and then the primary auditory cortex

Front 41

Inferior Colliculus (3)

Back 41

- in midbrain
- deals with auditory signal relay and acoustic reflexes
- there are both monaural and binaural neurons here

Front 42

what are the three themes present in the subcortical structures neural function?

Back 42

1) response modification- for localization and sound in noisy backgrounds, processing of cells in localized network of excitatory and inhibitory cells to "sharpen" features
2) tonotopicity- tonotopic map- change in frequency occurs along a particular spatial dimension like the basilar membrane. Especially in IC, where neurons are organized in to 2D planes called Isofrequency sheets.
3) Laterality- the extent to which the structures can be separately driven by two ears. Generally, neurons in higher structures are excited by contralateral info and inhibited by ipsilateral info

Front 43

Describe the descending pathways

Back 43

signals originate in cortex and flow down the subcortical structures
- involved in modulating the auditory response to sound in two ways:
- descending pathway controls firing rates in the ascending system by controlling the OC olivocochlear neurons (which give rise to the efferent neurons that innervate the cochlea)- largest effect at high frequencies
- motor neurons in brain stem stimulate contraction of tensor tympani and stapedius muscles in the middle ear which decreased sound transmission to prevent damage -largest effect at low frequencies

Front 44

Area A1, binural mixing here (5)

Back 44

- primary auditory cortex
- located along temporal lobe into Sylvian fissure
- tonotopic organization (neurons for low frequencies are anterior and high frequencies opposite)
- binaural (from both ears) inputs are combined using columns cells with summation response (when inputs form both ears are excitatory) and Suppression Response (neuron excited from input from opposite side but inhibited by stimulation on the same side)
- thus the A1 can be thought of as a two-dimensional sheet where sound frequency is along on axis and binaural mixing along the other

Front 45

conductive loss; sensorineural loss

Back 45

- outer of middle ear is affected, leading to reduced transmission to cochlea- would not be able to hear a tuning fork normally but if put to skull than could because it would stimulate cochlea directly and bypass outer ear; damage to cochlea or nerves of inner ear (hair cells) ex= NIHL (noise induced hearing loss), tinnitus (perception of ringing in ears)

Front 46

otitis media ; otosclerosis

Back 46

inflammation of eustachian tube that causes conductive hearing loss- more common in children; inherited bone disease causing abnormal development of ossicles which causes conductive loss

Front 47

tinnitus

Back 47

continuous ringing of ears- can be caused by damage to hair cells by ototoxic drugs (even advil in large doses), Ménières disease(excessive cochlear fluids)

Front 48

two major genetic causes of hearing loss

Back 48

Usher syndrome- deafness at birth or later in life caused by a recessive defective gene
Waardenburg Syndrome- dominant gene, causes hearing loss, weird hair and eye pigmentation

Front 49

Presbycusis

Back 49

hearing loss due to age

Front 50

3 requirements for us to hear a sound

Back 50

- there must be a sound source, there must be a medium that is propogates through, there must be a transduction mechanism

Front 51

Pressure ratio: how are pressures measured? formula for sound intensities? What is PR? explain formula

Back 51

IS/IR=PS squared/PR squared
where ps is the peak pressure of the sound we want to measure and pr is the reference pressure, usually 20upa micropascals, the smallest sound that can be heard.

Front 52

In general, doubling the sound pressure ...

Back 52

makes a sound 6dB louder

Front 53

complex harmonic sounds

Back 53

musical sounds which can be represented physically as a series of amplitude values in a harmonic spectrum

Front 54

Bony labyrinth; 2 subdivisions?

Back 54

cavity in the temporal bone with two subdivisions : the semicircular canals and the cochlea

Front 55

coding sound intensity (why do we have the range we do)

Back 55

- greater intensity produces greater deflection of basilar and tectorial membranes= increased neurotransmitter release
- we have a range of 120dBspl because we use different afferent nerve fibres:
-very sensitive fibres have a high spontaneous firing rate (rate they fire in quiet- high means they are sensitive) but saturate at low intensities
- then the relatively insensitive fibres take over, who have lower spontaneous firing, but saturate at higher intensities

Front 56

frequency coding; as sound gets louder...

Back 56

-A particular afferent fibre carries signals from a hair cell that was depolarized by the particular -sound frequency associated with its place in the tonotopic map
-as sound gets louder, the neuron becomes less frequency -selective, and more sensitive to sounds at lower frequencies