1
Q
as we age, our ability to hear higher frequency sound…
A
- disminishes
- younger ppl can hear high frequency sounds
2
Q
how does hearing vary across species?
A
- range of frequencies
3
Q
what happens when we blow a dog whistle?
A
- humans can’t hear it
- dogs can
4
Q
humans can perceive sound frequencies within this range:
A
20 - 20,000 Hz
5
Q
what animals have a wider and lower hearing range for frequency than humans?
A
- wider: whales, dolphins, dogs
- narrower: frogs, birds
6
Q
which animals can hear SIGNIFICANTLY more/less frequencies?
A
- more: bats, rodents
- less: fish
7
Q
in part, audible frequency range is determined by the…
A
evolution of the structures in the hearing system
8
Q
basilar membrane + how it varies in length
A
- contains hearing receptors
- sounds of diff. frequencies are processed along different areas of the basilar membrane
- varies in length across species
- shortest in amphibians/reptiles
- longer in birds, longEST in mammals
9
Q
which category of animals can discriminate the widest range of frequencies?
A
mammals
10
Q
how does sound travel?
A
waves
11
Q
how do sound waves compare to light waves
A
- travel slower
- require a medium to travel through
12
Q
how are sound waves initiated?
A
- vibrating object (burst of air, clap, guitar string, vocal chords)
- air molecules surround source of sound move
- this causes a chain reaction of moving air particles
13
Q
what interacts with the eardrum to begin auditory processing?
A
- alternating bands of dense/less dense air molecules (which come from the waves of sound)
- band of compressed air = eardrum pushed inwards
- band of less dense air = eardrum pushed outwards
14
Q
how can the changes in air pressure that make up a sound wave be graphed?
A
a sine wave
15
Q
what are the auditory equivalents of wavelength, amplitude, and purity?
A
- wavelength/frequency: pitch
- amplitude: loudness
- purity: timbre
16
Q
how does amplitude impact loudness?
A
higher waves = louder sounds
17
Q
how is loudness measured? why?
A
- logarithmic scale of decibels
- bc humans are sensitive to a wide range of sound amplitudes
18
Q
how do decibels work?
A
perceived loudness of a sound doubles for every ten decibel increase
19
Q
a normal conversation takes places at ___ dB
a whisper takes about ____dB
a concert is about ___dB
A
60
27
120
20
Q
can brief exposures to sound be damaging and painful?
A
yes
21
Q
how is pitch measured?
A
- in Hz
- Hz represents the number of cycles per second (peak to peak)
22
Q
relationship btwn frequency
(pitch) and wavelength
A
inversely proportional
23
Q
how does wavelength impact pitch?
A
- a short wavelength (peaks are close together) = higher frequency sound = high pitch
24
Q
pitch and frequency are….
A
directly proportional
25
the audible zone of frequencies that humans can detect represent…
- represent a portion of the sound frequencies tht can be produced
- just light the visible spectrum of light produces way more than what we perceive
26
how does purity impact timbre?
- timbre is our perceived complexity of a sound
- sound has fundamental tones and overtones (i.e. guitar)
27
why do a piccolo and a bassoon sound different to us, even if they play the same note?
- each instrument produces a unique combination of fundamental frequency and overtones
- even tho both r making sounds w/ same frequency/amplitude
28
three parts of the ear
- external ear
- middle ear
- inner ear
29
general process of how sound goes through the three parts of the ear
1. changes in air pressure are channeled through the outer ear into the middle ear
2. middle ear amplifies the sound so that…
3. inner ear detects changes in air pressure as changes in fluid pressure
4. changes in fluid pressure are converted into auditory neural impulses
30
parts/functions of the external ear
- pinna
- ear canal
- ear drum (tympanic membrane)
31
pinna
- external ear
- collects sound waves in environment and directs them along ear canal
- comes in various shapes
32
ear canal
- external ear
- amplifies the incoming sound waves (like a horn)
- narrows as it moves towards ear drum
33
ear drum/tympanic membrane
- external ear
- forms back wall of ear canal
- thin membrane that vibrates at frequency of incoming sound wave
34
parts of middle ear
- hammer
- anvil
- stirrup
- these are all called “ossicles” and begin after the ear drum
35
how do the ossicles work?
- ossicles are 20x larger than the oval window (where they connect)
- creates a “lever” system
- the lever system amplifies the vibrations even more for the oval window
36
oval window
- connects to the cochlea of the inner ear
- is a small opening in the side of the cochlea
- when it vibrates, fluid inside of the cochlea gets displaced
37
cochlea
- inner ear
- fluid filled tube
- 35mm long
- coiled like a snail shell
- contains neural tissue that will transfer changes in fluid motion to neural impulses
38
what happens when the fluid inside the cochlea is displaced?
- causes an increase in pressure
- there is a also round window in the cochlea which bulges in/out to accommodate for fluid movement
- inside the cochlea is the basilar membrane
- when oval window is pushed inwards, fluid waves push basilar membrane downwards
- when oval window is pushed outwards, fluid waves push basilar membrane upwards
39
the cochlea gets narrower towards the end. however, the basilar membrane…
- gets wider towards the end
- membrane varies in flexibility and width = diff regions vibrate for diff frequencies of sound
40
what areas of the basilar membrane vibrate for which frequencies?
- high frequency: end closest to window openings
- low frequency: end closest to apex
41
large things generally produce…
lower frequency sounds
42
what ,on the basilar membrane, converts the physical stimulus into neural impulses
hair cells
43
what does the basilar membrane house? how do they work?
- auditory receptors called hair cells
- these cells move as the basilar membrane moves in response to sound
- the movement is converted into neural impulses that the brain can understand
- these hair cells are connected to nerve fibers
- the hair cell releases a neurotransmitter
44
which cells do hair cells synapse with? wht do those make up?
- bipolar cells
- their axons make up the cochlear nerve (branch of main auditory nerve)
45
ratio of outer to inner hair cells
- outer cells outnumber, four to one
- inner hair cells mainly contribute to cochlear nerve
46
differences btwn outer and inner hair cells
inner:
- communicates with 20 afferent fibers = 20 direct links to brain
- less numerous, but more connections to brain
- send info abt pitch
- synapse with thick, myelinated axons
outer:
- share one direct link to brain with 30 other hair cells
- more numerous, but less connections to brain
- amplify sound
- synapse with thin, unmyelinated axons
47
are inner or outer hair cells more responsible for transmitting the auditory signal to the brain?
inner hair cells
48
what does the neurotransmitter released by hair cells do?
- trigger EPSPs in cochlear nerve fibers
- signal is sent to cochlear nucleus in hind brain
49
streams of cochlear nucleus
- dorsal
- ventral
50
similarities btwn visual and auditory streams
- dorsal/ventral streams
- topographical and tonotopic (organized neural representations)
51
tonotopic organization
- frequency coated along diff regions of basilar membrane
- hair cells connect to cochlear nerves such that neighboring regions stay together
- organization is maintained to primary auditory cortex
52
base/apex of cochlea and area 1
- base of cochlea = narrowest part = high frequency —> end of area one (A1)
- apex of cochlea = widest part = low frequency —> other end of area one (A1)
53
what does auditory localization depend on? hows it diff from visual?
- our sense organs are separated in space
- inter-aural diffs btwn ears
- unlike vision, there’s no direct spatial representation of the stimulus
- like vision, audition uses stimulus disparity as a cue
54
inter-aural cues
- difference it takes for sound to reach each ear
- difference in intensity btwn two ears, esp for high frequency sounds
- pinna cues
55
how does the difference it takes for sound to reach each ear impact auditory localization
- sound takes longer to reach further ear
- slight difference measured in sub milliseconds
- specific neurons in Superior Olivary Complex react to those slight differences
56
how does the difference in intensity btwn two ears impact auditory localization
- loss of intensity occurs btwn two ears for high frequency sounds
- difference in intensity caused by head impacts the ears, which casts a sound shadow on the distal ear
- doesn’t occur for low frequency sounds because wavelengths longer than head diameter can diffract around head without losing its intensity
57
when localizing low frequency sounds, wht becomes more critical?
time difference it takes to reach each ear
58
what side of the brain does input from each ear travel to? what does this help with?
- both sides
- differences in intensity can be directly compared to calculate location of sound
59
what do the neurons in the Super Olivary Complex respond to?
- some respond specifically to intensity differences from each ear
- some respond specifically to inter-aural differences in arrival times
60
what happens when sound is directly in front or behind of us?
- strikes both ears at the same time
- becomes difficult to locate the source of the sound
- rotating head slightly causes slight changes in sound intensity reaching each ear
61
how do pinna cues impact auditory localization
- pinna defracts incoming sound waves
- this makes changes to frequency content of sound that reaches inner ear
- some are attenuated and others are amplified
- required for determining location and elevation of sound source
- sound is uniquely transformed by pinna shape
62
what are pinna shapes sometimes called?
- ear prints
- bc everyone has a diff ear shape
63
what happens when pinna moles ar placed in the ear?
- disorienting effect on localization ability
- even tho inter-aural diffs are available
- over a few weeks participants can adapt to new pinna cues and localization becomes normal again
- when molds are removed, participants have impaired ability again and must re-adapt
64
which animal is a master of maneuvering in the dark?
bats
65
bats + what they can do
- 40 cm wingspan bats can fly through a 14x14cm opening in a grid in total darkness
- they use echolocation
66
echolocation
- receiver emits sound pulses and analyzes returning echo to for a perceptual image of objects in the environment
- close objects return the echo faster
- moving objects return echos w/ doppler shift
- textured objects return echos that vary in return times
67
adaptations of bat prey
- evolved sense of hearing to detect bat specifically
- i.e. moths can hear sounds tht match frequency range used by bats when they’re hunting insects
68
co-evolution
process by which evolution and adaptation of traits of one species can directly affect the evolution of traits in another species
psych 1xx3
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