Hearing Flashcards
(70 cards)
1
Q
What is a sound wave?
A
- when an object vibrates, it causes molecules in the surrounding air to alternately condense and rarefy (pull apart)
- these fluctuations in air pressure give rise to a sound wave
- it travels away from the object at approximately 700 miles per hour
2
Q
When can the human ear transduce fluctuations in air pressure?
A
- when the length of the sound wave is between 0.017 (17 mm) and 17 meters long
3
Q
What causes a sound wave to be between 0.017 and 17 metres long?
A
- when physical objects vibrate between 20 and 20,000 times per second
4
Q
What are the 3 physical dimensions of sound?
A
- loudness
- pitch
- timbre
5
Q
What is loudness?
A
- the amplitude or intensity of the molecular vibrations
- the relative difference in the density of air molecules between compressed and rarified air
- determines how far the sound wave will travel
6
Q
What is pitch?
A
- tone
- the frequency of the molecular vibrations (or the distance between neighboring peaks of compressed air)
- measured in hertz (Hz, cycles per second)
- every frequency has a corresponding wavelength
7
Q
What is timbre?
A
- the complexity of the sound wave
- brains learn to recognize the timbre of sound waves to identify the source of the sound
8
Q
What is noise?
A
- non-repeating variations in air pressure are perceived as noise, not as identifiable notes
9
Q
What are notes?
A
- repeated variations in air pressure
10
Q
What is the anatomy of the ear?
A
- outer ear
- middle ear
- inner ear
11
Q
What is the outer ear made of?
A
- pinna
- ear canal
- eardrum
12
Q
What is the middle ear made of?
A
3 ossicles:
- malleus
- incus
- stapes
13
Q
What is the inner ear made of?
A
- cochlea
14
Q
How does sound travel through the ear?
A
- sound is funneled through the pinna
- at the end of the ear canal, sounds cause the tympanic membrane to vibrate
- vibrations transfer to the middle ear and cause the ossicles to vibrate
- cause the membrane behind the oval window to vibrate
- vibrations of the oval window are transmitted to the fluid-filled cochlea
15
Q
What is the basilar membrane?
A
- sheet of cells
- neurons that detect sound
- designed to respond to waves through cochlea
- bends with vibrations (fast/high notes = bend at base, slow/low notes = bend at apex)
16
Q
Where in the basilar membrane are high pitched notes detected?
A
- where the basilar membrane is thick, narrow and tight (closest to the oval window)
17
Q
Where in the basilar membrane are low pitched notes detected?
A
- where the basilar membrane is thin, wide and loose
18
Q
What are the 3 longitudinal divisions of the cochlea?
A
- scala vestibuli
- scala media
- scala tympani
19
Q
What is the organ of Corti?
A
- the receptive organ
- consists of the basilar membrane on bottom
- tectorial membrane on top
- auditory hair cells in the middle
20
Q
What are hair cells?
A
- cells that transduce sound
21
Q
What are cilia?
A
- the hair cells hair-like extensions
22
Q
What are the cilia on the outer hair cells?
A
- attached to the rigid tectorial membrane
23
Q
What are the cilia on the inner hair cells?
A
- not attached to anything
- sway back and forth with the movement of the solution
24
Q
How do sound waves effect organ of Corti?
A
- sound waves cause the basilar membrane to move relative to the tectorial membrane
- causes hair cell cilia to stretch and bend
- movement of the cilia pulls open ion channels, which changes the membrane potential of hair cells
25
How many hair cells are there?
- 3 times more outer hair cells than inner hair cells
26
What are outer hair cells?
- act like muscles to adjust the sensitivity of the tectorial membrane to vibrations
- regulating the flexibility of the tectorial membrane
- influence the sensitivity of inner hair cells to specific frequencies of sound
27
What are inner hair cells?
- transmit auditory information to the brain
- perception of hearing comes from inner hair cells
28
What happens to people who do not have working inner hair cells?
- completely deaf
29
What happens to people who do not have working outer hair cells?
- can hear, but not very well
30
What are tip links?
- connect the cilia of hair cells to each other
- elastic filaments that attach the tip of one cilium to the side of adjacent cilium
31
What is the insertional plaque?
- the point of attachment of a tip link to a cilium
- each one has a single ion channel in it that opens and closes according to the amount of stretch exerted by the tip link
32
What happens when there is a loud noise?
- loud noises can easily break the tip links
- hair cells cannot transmit auditory information without tip links
- tip link breakage generally corresponds to temporary hearing loss
33
How fast to tip links grow back?
- within a few hours
34
Why do the tip links break?
- protective measure
- because too much glutamate release onto the cochlear nerve causes permanent cell death
35
How many 20 year olds have noise-induced hearing loss?
- 20% of 20 year olds
- presumably due to cochlear nerve damage
36
What is the major principle of auditory coding?
- different frequencies of sound produce maximal stimulation of hair cells at different points on the basilar membrane
- place coding
37
What is place coding?
- approach to encoding sensory information
- the position of the most active hair cell in the cochlea indicates the fundamental frequency (the pitch) of the sound wave
38
How are moderate to high frequencies encoded?
- entirely encoded by place coding
- human speech is in this frequency range
39
How are very low frequencies encoded?
- largely encoded by rate coding
40
How does place coding work in the auditory system?
- acoustic stimuli of different frequencies cause different amounts of movement along the basilar membrane
- higher frequency sounds cause bending of the basilar membrane closest to the stapes, resulting in more hair cell activity in that area
41
How does rate coding work in the auditory system?
- the pattern of neurotransmitter release from the hair cells deepest in the cochlea (furthest from the stapes) determines the perception of low frequency sounds
42
What is the sensitivity of three individual inner hair cells, as shown by their response threshold to pure tones of varying frequency?
- one inner for every 3 outer??
- low points indicate that these inner hair cells will respond to faint sound only if it is of a specific frequency
- when sound is louder, cells will respond to frequencies above and below their preferred frequencies
- lesions in outer hair cells will disrupt the responsiveness of inner hair cells to specific sounds (only react to louder sounds and most activated at a different frequency)
43
How is pitch perception encorded?
- moderate to high frequencies are encoded by place coding
- low frequencies are partly encoded by rate coding
44
What does loudness correspond to?
- the total number of hair cells that are active and their overall activity levels
45
How is timbre perceived?
- by assessing the precise mixture of hair cells that are active throughout the entire cochlea
46
What is the fundamental frequency?
- the lowest frequency in the sound wave
- most intense frequency of a complex sound
- perceived as sound's basic pitch
47
What are natural sounds comprised of?
- a fundamental frequency
- a collection of overtones
48
What are overtones?
- sound wave frequencies that occurs at integer multiples of the fundamental frequency
- because strings (and membranes) are clamped on each end, oscillations tend to only occur at integer multiples of the fundamental frequency
49
What does the timbre of sound refer to?
- specific mixture of frequencies (fundamental frequency plus overtones) that different instruments emit when the same note is played
- complexity of the sound wave
50
How do we identify which instrument made the sound?
- analyze the timbre of a sound and how the timbre changes over time
51
What are cochlear implants?
- take advantage of the place coding system of the cochlea
- elicit the perception of different notes by stimulating different places along the cochlea
- loudness is controlled by the frequency of stimulation
52
What is the fundamental frequency of human speech?
- 100-250 Hz
53
How do cochlear implants understand human speech?
- understanding human speech is often best when positions corresponding to 250 Hz to 6500 Hz are stimulated
54
How do we identify the direction of a sound (localize sound)?
- interaural cues
- analyzing the timing difference between the 2 ears (which ear heard the sound first)
55
What are interaural cues?
- differences in sound perception between the two ears
56
How do we localize high frequency sounds (> 800 Hz)?
- use interaural loudness differences (which ear heard it louder)
- the loudness of a high-pitched (high frequency) sound is significantly dampened by the head
57
How do we localize low frequency sounds (< 800 Hz)?
- the brain analyzes the phase difference between the two ears
- listen over a longer time to know which ear heard it first
- wavelengths that are longer than the width of the head
58
How do we identify the height of a sound?
- analyze the timbre of the sound wave
- shape of our outer ear creates a direction-selective filter
- different frequencies are enhanced/attenuated when sound enters our ears from different directions
- highly individual
- not born with this skill; must learn by integrating visual and auditory perceptions
- abrupt changes in the shape of your outer ear can make it difficult to accurately localize the elevation of sounds
59
What is a direction-selective filter?
- different frequencies are enhanced/attenuated when sound enters our ears from different directions
60
How does auditory information travel from the ear to brain?
- organ of Corti sends auditory information to the brain via the cochlear nerve
- axons synapse in the cochlear nuclei (in medulla), where copies of the signal are made to be analyzed in parallel ascending paths
- axons from the cochlear nuclei synapse in the superior olivary nuclei (in medulla) and the inferior colliculi (in midbrain)
- axons from the inferior colliculi synapse in the medial geniculate nucleus (in thalamus)
- thalamus relays the information to the primary auditory cortex (in temporal lobe)
61
What do the superior olivary nuclei (in medulla) and the inferior colliculi (in midbrain) help do?
- help localize the source of sounds
62
What is tonotopic representation?
- the primary auditory cortex is organised according to frequency
- different parts of the auditory cortex respond best to different frequencies
- different frequencies of sound are analyzed in different places of auditory cortex
63
Where is the primary auditory cortex?
- core region
- in the upper section of the temporal lobe, mostly hidden in the lateral fissure
64
Where is the auditory association cortex?
- belt and parabelt regions
65
What is the posterior dorsal auditory pathway?
- involved in sound localization
- where stream
- meets up with the “where” vision pathway in the parietal lobe
- temporal to parietal lobe
66
What is the anterior auditory pathway?
- important for recognizing what produced a sound
- what stream
- temporal to frontal lobe
67
What causes auditory agnosia?
- brain damage in auditory association cortex
68
What are the types of auditory agnosia?
- amusia
69
What does the auditory association cortex process?
- different areas process the melody, rhythm, and harmony (overtones) of music
- other areas are involved in the perception of sound as pleasant (consonant) or unpleasant (dissonant), and certain combinations of musical notes can trigger emotions (happy or sad)
70
What is amusia?
- the inability to perceive or produce melodic music
- unable to sing or recognize a song
- can often converse and understand speech and recognize environmental sounds
- can recognize the emotions conveyed in music
- unable to tell the difference between consonant music (pleasant sounding harmony) and dissonant music (unstable, transitional), even though these sounds might alter their emotional state
