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2115 sensation & perception > Week 8 : Intro to the Auditory System > Flashcards

Week 8 : Intro to the Auditory System Flashcards

1
Q

Auditory landscape…

A
  • the first challenge in the auditory system is to correctly identify the source of a sound…
  • this includes the identity and the location of a sound producing object & how to best interact with it
  • difficult cuz our environments very often contain sounds produced by multiple objects at the same time
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2
Q

Sound medium…

A

there needs to be a medium, such as air or water, to conduct sound… in the absence of such a medium sound cannot exist
- more include bones, water, traintracks (anything that can vibrate)
- water transmits sound 4x faster than air does

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3
Q

Sound stimulus…

A

the periodic variations in air pressure travelling out from the source of the variations…
- these periodic variations in pressure are the sound wave
- the source of the variations is the object making the sound

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4
Q

Overtime air pressure will increase and decrease slightly…

A

these small changes in air pressure constitute sound to our ears if they occur strongly enough + quickly enough

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5
Q

the physical stimulus that gives rise to perception of sound is comprised of…

A

alternating patterns of high and low density air molecules generated by the movement of a stimulus in the environment

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6
Q

Think of music playing off of a loud speaker…

A
  • speaker vibrates cuz it produces sound by moving a diaphragm inward and outward
  • as the diaphragm pushes outward, it compresses those air molecules directly in front of it
  • it then pulls backward + produces a local region of lower air density
  • by repeating this pattern over and over, the speaker produces the same pattern of alternating compressions and rarefactions
  • this then travels from the speaker to your ear
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7
Q

visualizing sound

A
  • wave form
  • density plotted over time
  • peaks correspond to point of maximal compression and valleys correspond to point of lowest density
  • midpoint of the waveform corresponds to the normal air pressure (average before speaker started moving)
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8
Q

physical attributes mapping onto perceptual attribute… (3)

A
  1. Amplitude = Loudness
  2. Frequency = Pitch
  3. Waveform = TImbre
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9
Q

Pure tones are…

A

sound waves in which air pressure changes follow the basic sine wave format… it is heard at a particular pitch

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10
Q

Frequency…

A
  • The number of cycles (full wavelengths) in a sound stimulus that occur in one second
  • we express this using Hertz ^^
  • perceptual correlate is pitch
  • long wavelength = low frequency + pitch… short wavelength = higher frequency + pitch
  • lost higher frequencies after age 20
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11
Q

frequency, hertz

A
  • we are able to discriminate very small frequency differences in Hz
  • the sound frequencies to which we are sensitive is labelled the audible spectrum… 20-20,000Hz
  • the range of frequencies the system is capable of perceiving
  • BUT we are not equally sensitive across the entire range
  • while frequencies at the lowest end of the audible range do not become perceivable until about 70dB, our sensitivity is best around 3000-4000Hz
  • other animals have way cooler ranges
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12
Q

Amplitude

A
  • the size of the peaks and valleys of the waveform relative to normal air pressure
  • the difference between its maximum and minimum sound pressures
  • there can be small and large amplitude waveforms of the same frequency
  • Loudness is there perceptual experience
  • usually measured in decibels (dB)
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13
Q

Sound level (decibels)

A
  • sound level is expressed using a scale called the decibel scale
  • it is logarithmic, which means that for every change if 10 decibels… there is a 10 file increase in sound power
  • 0 = threshold level (quietest possible sound that can be heard)… 130 = plane taking off
  • we are really good at detecting differences, we can discriminate a difference of just 1 dB
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14
Q

Sounds too loud

A
  • many of our common listening experiences reach well into the danger zone, where sound levels can cause permanent damage
  • because high amplitude can result in permanent damage, occupational health standards organizations provide guidelines for the max amount of time that u should be exposed to diff sound levels
  • sustained exposure over 85dB potentially damaging
  • 8 hour work day=85dB… 30 seconds at 115dB
  • listening volumes depend on the ambient noise level where you’re listening so use noise cancelling headphones wherever possible
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15
Q

Timbre (shape of the waveform)

A
  • the shape can vary from a simple sinusoid or sine wave which would perceive as a pure tone of a single frequency to…
  • complex waveforms
  • the differences in sound character that arise from these differences in shape of the underlying waveform are often referred to as timbre
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16
Q

Sine waveforms…

A
  • simplest way to illustrate a sound wave
  • but… these types of pure tones (single sound frequency) are super uncommon in nature
  • instead… nearly all naturally occurring sounds have a mix of different sound frequencies + would be better illustrated by a complex waveform
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17
Q

Complex waveforms

A
  • nearly all sounds that have pitch consist of multiple sound frequencies
  • these frequency components have a harmonic arrangement
  • so… the sound has a composite waveform at the bottom, consisting of a fundamental frequency (first harmonic) and also has several other harmonics that are multiples of that fundamental
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18
Q

Fourier analysis for complex waveforms

A
  • math procedure for taking any complex waveform and determining the simpler waveforms that make up that complex pattern
  • break down complex sound into fundamental frequency and harmonics
  • fundamental frequency… (pitch) lowest frequency present in the complex sound, determines pitch
  • harmonics… (timbre) all frequencies present in the stimulus that are higher in frequency than the fundamental
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19
Q

Phase

A
  • refers to the position in one cycle of a wave
  • a given sound wave is in the alternating pattern of compressions and rarefactions at a given point in time
  • if waveform A is at its peak and B is at its valley at the save time and vice versa…
  • the result is that one waveform cancels out the other so we don’t perceive any sound
  • this is the basis of sound cancelling headphones (playing opposite phase sounds to ones in the environment)
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20
Q

Anatomy of the ear

A

goal is to understand how sound waves are translated into electrical potentials that communicate info abt our environment, complementing the types of into we perceive from visual cues

21
Q

structures of auditory system broken into 3 component sections…

A
  1. outer ear… pinna, ear canal +tympanic membrane (eardrum)
  2. middle ear, 3 smallest bones in the body
  3. inner ear… cochlea, site of sound transduction
22
Q

Pinna (outer ear)

A
  • outer most portion of ear that sticks out of head is called the pinna
  • funnels sound into the ear canal
  • ridges of the pinna play a role in shaping the distribution of sound harmonics
  • size & shape of pinna vary widely across species
23
Q

Ear canal (outer ear)

A
  • sound that reach the pinna are directed down the ear canal
  • 25mm long
  • helps amplify certain higher frequencies
  • protects the tympanic membrane
24
Q

Tympanic membrane or eardrum (outer ear)

A
  • sound travels down ear canal and the pattern of air compressions and rarefaction acts to vibrate the tympanic membrane
  • thin elastic sheet that vibrates in response to sounds coming through canal
  • seals the outer ear
  • damaging it results in hearing loss (e.g. scuba divers from pressure) but in most cases it will repair itself
25
Q

middle ear

A

middle ear is an air-filled chamber that fills the gap between the tympanic membrane and the cochlea
- contains 3 tiny bones called auditory ossicles

26
Q

Ossicles (middle ear)

A
  • Malleus (hammer), Incus (anvil) and stapes (stirrup)
  • one of principle functions of the ossicles is to transmit and amplify sounds between the outer and inner ears
  • necessary cuz the inner ear is a fluid filled chamber (sound travels well in water but does not cross from air to water well… 90% will bounce off water rather then penetrate it)
  • the 3 bones + ligaments that connect them create a small lever system to increase the amount of pressure change
  • the ossicles transfer energy from a larger surface area (tympanic membrane) to a smaller surface area (oval window of cochlea)
  • tympanic membrane abt 18x as big as oval window so bones increase sound pressure 18x at oval window (size difference)
27
Q

Eustachian tube (middle ear)

A
  • tube that connects the middle ear with the pharynx and serves to equalize air pressure on either side of the tympanic membrane
  • normally it is closed but opens briefly when we swallow or yawn (popping ur ears)
  • for optimal operation of the tympanic membrane, air pressure of both sides needs tone equal
  • outside air pressure changes from weather + altitude … so the Eustachian tube opens to allow air pressures to equalize
  • If your eustachian tubes stay closed, youll have much air pressure on the middle-ear sides than outside, causing them to bow toward the outside of your head
  • Being pushed out causes the tympanic membrane to move less effectively in response to sound stimuli (trouble hearing)
28
Q

ossicles in attenuating sustained loud sounds…

A
  • muscle attaches to malleus called tenor tympani and one attached to stapes called stapedius
  • job is to tense in a presence of very loud noises, thus restricting the movements of the ossicles and avoid damaging the inner ear
  • acoustic reflex that protects somewhat against chronic loud noises, but is too slow for sudden loud noises
  • may also tense in response in sounds generated inside the head
29
Q

Inner ear (cochlea)

A
  • the stapes transmits the mechanical sound waveform to the cochlea of the inner ear
  • the cochlea is an extremely complex structure
  • the stapes bone rests on another small membrane called the oval window
  • stapes pushes the oval window in and out in response to movement of the tympanic membrane from sound
  • movement of the oval window causes the fluid that fills the cochlea to move in a similar wave-like fashion (perilymph)
  • cochlea consists of 3 canals… the movement of fluid thru these canals causes a displacement of the basilar membrane at its centre
30
Q

cochlea more

A
  • snail shaped structure
  • coils 2.74 times
  • takes up about 4mm of space in the ear
  • 3 liquid filled chambers called… tympanic canal, middle canal and vestibular canal
  • apex = end of cochlea… opening called helicotrema that allows fluid to flow between tympanic canal and vestibular canal
  • just under oval window is round window… soft tissue substance at base of tympanic canal (escape valve for pressure)
31
Q

Basilar membrane

A
  • runs down centre of cochlea
  • sensory cells highly organized
  • basilar membrane arranged by sound frequency
  • with hair cells that are sensitive to high-frequency sounds at the base, near the oval window (20,000Hz)
  • with hair cells sensitive to lower frequency sounds located at the apex (80Hz)
32
Q

Basilar membrane organization…

A
  • imagine unrolling it…
  • stapes bone pushes oval window, causing fluid to displace in a rhythmic pattern
  • while the waves go along the basilar membrane, the hair cells are stimulated at a region that corresponds to the frequency of that sound
  • cuz…
  • near base of cochlea, membrane thick and rigid, so high frequency waves cause greatest amount of movement
  • at the apex, membrane thinned and more flexible, so lower frequency sounds cause the greatest displacement
  • any sound will move the basilar membrane at every location, but a particular location will respond the most to its characteristic frequency
33
Q

Membrane dynamics…

A
  • sound induced signals are produced along the basilar membrane at the point of its maximal displacement, this differs by sound frequency
  • the basilar membrane and the hair cells that line it are able to pull apart the incoming sound to provide a reliable representation of sound frequency
34
Q

Organ of Corti

A
  • located in the basilar membrane
  • hair cells are arranged along the membrane in 4 rows… 1 row of inner hair cells + 3 rows or outer hair cells
  • the 2 cell subtypes play very different roles in the process of auditory perception
  • the whole cell system is covered by a tectorial membrane which rests on top of the hair cells and creates the shearing force necessary for cell signalling
35
Q

Inner hair cells

A
  • primary sensory cells of auditory system
  • cells that depolarize in response to sound in their preferred frequency
  • this depolarization sends a signal up to higher level auditory processing regions of brain via type 1 auditory nerve fibers
36
Q

outer hair cells

A
  • play a role in amplifying sound signals being transmitted by neighbouring inner hair cells
  • type 2 auditory nerve fibres target outer hair cells
37
Q

Signal generation…

A
  • the hair cells of the cochlea are called that cuz on top of them are lines of stereocilia that look like little hairs (each hair cell has anywhere from 50-150)
  • these stereocilia make contact with the tectorial membrane which moves back and forth with the upward + downward movements of the basilar membrane
  • the movement of the basilar + tectorial membranes causes the little hairs on top of the hair cells to bend in one direction or the other
  • the movement of them in 1 direction, causes depolarization of the hair cells and an increase in the # of action potentials generated in type 1 nerve fibres that correspond to that cell
  • movement in the other direction reduces nerve cell firing
  • PLACE CODE THEORY
38
Q

Spiral ganglia & auditory nerve

A
  • final step in sound transduction occurs when signal generated by depolarized inner hair cells is picked up by the type 1 nerve fibres that extend from spiral ganglion neurons
  • spiral ganglion neurons are the first neurons in the auditory pathway
  • these ganglion cells cover the entire length of the basilar membrane, come together and exit the cochlea as the auditory nerve
  • the auditory nerve carries sound related activity to auditory regions of the brain
39
Q

Audiogram

A
  • measure of how well someone can hear
  • created by presenting sounds of varied frequencies at different levels, in order to find a threshold (method of limits)
  • we can hear up to 20,000Hz but usually audiograms go to about 8,000Hz (important for speech comprehension)
  • Audiograms are plotted with small values up top, so as you move toward the bottom of the plot, the sound levels (decibels) required to elicit a response get larger and larger
  • presbycusis common in audiograms
40
Q

Presbycusis…

A
  • age-related hearing loss
  • may already be experiencing this from wear + tear
  • more common in men
  • hair cells degrade over time and with use, particularly at the base of the cochlea where high frequency sounds are represented
  • They cannot be repaired or replaced as of yet, so the damage accumulates over the lifespan
41
Q

Hyperacusis

A
  • persistent percept that sounds presented at otherwise normal levels are exceedingly loud
  • wide range of causes (head injury, infection, mental health, etc.)
  • can lead to a great deal of anxiety & inability to engage with ppl in noisy environments
42
Q

Tinnitus

A
  • the perception of a sound in the absence of a sound source
  • often described colloquially as ringing of the ears, but perceived sound can acc have a wide variety of presentations
  • huge number of people experience some degree of tinnitus and it is very often reported by those who also have hearing loss
  • can have serious mental health impacts
  • treatment may include hearing aids
43
Q

conductive hearing loss…

A
  • characterized by damage to some aspect of sound transmission in the outer or middle ear
  • Sound does not properly get to the cochlea for transduction into a neural signal
  • May occur cuz of otosclerosis… An inherited bone disease in which the ossicles (stapes in particular) may calcify and therefore be less conductive of sound
  • Can be improved by replacing the stapes with an artificial bone
  • Also conditions in which hearing loss may occur on a temporary basis
44
Q

Sensorineural hearing loss…

A
  • occurs because of damage to the cochlea, auditory nerve or primary auditory cortex
  • Acquired hearing problems and genetic problems
  • Most often precipitated by damage to hair cells
  • Can occur cuz of noise exposure or certain drugs
45
Q

Amplification

A
  • most common tech to address hearing impairments is sound amplification by providing a hearing aid
46
Q

hearing aids

A
  • come in a number of forms
  • in ear/behind pinna
  • fitted to an individuals hearing loss such that they amplify sounds of particular frequencies in order to boost those thresholds back into the normal range
  • However, in many cases, the damage to the region of the cochlea is so extensive that no amount of amplification will restore normal threshold
  • in this case, advanced tech is used to compress the incoming sound info such that info that would normally be perceived by the impaired region of the cochlea gets shifted downward in pitch such that it stimulates an intact region of the membrane
  • This often distorts the harmonic arrangement tho and can have dramatic impact on a sounds timbre
47
Q

Cochlear implants

A
  • For ppl who wouldn’t benefit from a hearing aid, such as those born without bones of the middle ear, or ppl with non functional hair cells
  • consist of a microphone, worn in back of ear like a hearing aid
  • transmit sound into through the skull to an implanted stimulator which is attached to an electrode implanted directly into the cochlea
  • The electrode is able to bypass damaged hair cells and directly stimulate spiral ganglion neurons initiating a cascade of signaling that results in sound perception
48
Q

speech scores…

A
  • Despite replacing the rich frequency-based organization of the cochlea, with only a handful of stimulating electrodes, cochlear implants are incredibly able to restore functional perception of sound
  • children who receive implants very early in childhood, go on to show normal receptive language scores within a year and a half
  • This is an amazing achievement

2115 sensation & perception (14 decks)

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