chapter 11 pt 2

Question 1

Békésy’s place theory of hearing

Answer 1

frequency of sound is indicated by the placed on the organ of corti that has the highest firing rate

different parts of the membrane vibrate the most depending on the frequency

Question 2

tonotopic map

Answer 2

the cochlea shows an orderly map of frequencies along its length
- apex responds best to low frequencies
- base responds best to high frequencies

Question 3

frequency tuning curves

Answer 3

we can determine the threshold for specific frequencies for single neurons

done by presenting pure tones of different frequencies and measuring the sound level necessary to cause the neuron to increase its firing above the baseline or “spontaneous” rate in the absence of sounds

the level = threshold for that frequency

plotting each threshold for each frequency = frequency tuning curve

Question 4

characteristic frequency

Answer 4

frequency to which the neuron is most sensitive

Question 5

place theory

Answer 5

based on the relation between a sound’s frequency and the place along the basilar membrane that is activated

Question 6

phase locking

Answer 6

because nerve fibers fire at the same time in the sound stimulus, the sound produces a pattern of nerve firing in groups of neurons that matches the frequency of the sound stimulus

= bursts of firing and not firing

the timing of firing of groups of neurons provides information about the fundamental frequency of a complex tone, and this information exists even if the fundamental frequency or other harmonics are absent

Question 7

which area of the basilar membrane responds best ot low frequencies

Answer 7

the apex

Question 8

which area do the basilar membrane responds best to high frequencies

Answer 8

the base

Question 9

how does the cochlear act like a filter

Answer 9

the different places of maximum vibration along the length of the basilar membrane separate sound stimuli by frequency

• high freq = more vibration near the base
• low freq = more vibration near the apex

means that vibration of the membrane sorts or filters by frequency so hair cells are activated at different places along the cochlea for different frequencies

Question 10

what are two things that reflects the cochlea’s filtering action

Answer 10

1. the neurons respond best to one frequency
2. each frequency is associated with nerve fibres located at a specific place along the basilar membrane, with fibers oringinating near the base of the cochlea having high characteristic frequencies and those originating near the apex having low characteristic frequencies

Question 11

what is the main purpose of outer hair cells

Answer 11

to influence the way the basilar membrane vibrates by changing length

the mechanical response of their longening and shortening pushes and pulls on the basilar membrane, which increases the motion of the basilar membrane and sharpens its response to specific frequencies

Question 12

how do outer hair cells change length

Answer 12

ion flow in outer hair cells causes mechanical changes inside the cell that causes the cell to expand and contract

the outer hair cells become elongated when the stereocilia bend in one direction and contract when they bend in the other direction

Question 13

cochlear amplifier

Answer 13

outer hair cells make the basilar membrane more sensitive to different frequencies and play and important role in the frequency selectivity of auditory nerve fibers

without outer hair cells, it would take much higher intensities of sound to get auditory nerve fibers to respond

Question 14

missing fundamental

Answer 14

critique of place theory
- effect where removing the fundamental frequency of a complex tone does not change the tone’s pitch - means there isn’t a peak vibration at the place associated with the pitch because there isn’t a fundamental frequency entering the ear

Question 15

how does place theory address the missing fundamental

Answer 15

complex tones cause peaks in vibration for both the fundamental and the harmonics - we can still determine the pitch without the fundamental by recognizing the pattern of peaks in the harmonics

this only works for low harmonics, however! these are called resolved harmonics

can’t fully explain missing fundamental

Question 16

resolved harmonics

Answer 16

harmonics in a complex tone that create separated peaks in basilar membrane vibration and so can be distinguished from one another - usually lower harmonics of a complex tone

Question 17

unresolved harmonics

Answer 17

higher harmonics of a complex tone that don’t create separate peaks in basilar membrane vibration and can’t be distinguished from each other - result in a weak perception of pitch without the fundamental frequency

Question 18

amplitude modulated noise

Answer 18

critique of place theory

a stimulus that doesn’t create vibration pattern on the basilar membrane that corresponds to a specific frequency since it is made up of so many random frequencies and that fluctuates between different levels of loudness

we can still determine pitch from this type of noise

Question 19

how is phase locking linked to pitch perception

Answer 19

they both only occur for frequencies up to about 5000Hz

when tones are strung together to create a melody, we only perceive a melody if the tones are below 5000Hz

our sense of musical pitch may be limited to those frequencies that create phase locking

Question 20

temporal coding

Answer 20

the connection between the frequency of a sound stimulus and the timing of the auditory nerve fiber firing

Question 21

where do signals generated in the cochlea go?

Answer 21

transmitted out of the cochlea in nerve fibers of the auditory nerve

they get carried along the auditory pathway, eventually reaching the auditory cortex

Question 22

what is the sequence of subcortical structures that auditory nerve fibers synapse in

Answer 22

cochlear nucleus > superior olivary nucleus in the brain stem > inferior colliculus in the midbrain > medial geniculate nucleus in the thalamus

Question 23

where do auditory nerve fibers go after the medial geniculate nucleus

Answer 23

primary auditory cortex in the temporal lobe of the cortex

Question 24

what is the function of processing in the superior olivary nucleus

Answer 24

this is the first place that signals from the left and right ears first meet so it is important for locating sounds

Question 25

what happens as nerve impulses travel up the SONIC MG pathway to the auditory cortex?

Answer 25

temporal information decreases

phase locking, which occured up to about 5000Hz in auditory nerve fibers, occurs only up to 100-200Hz in the auditory cortex

however, there are areas of the auditory cortex that respond to pitch

Question 26

pitch neurons

Answer 26

cortical neurons in marmoset (monkeys) that respond to stimuli associated with a specific pitch - they fire at the pitch of a complex tone even if the harmonic or other harmonics of the tone are not present

Question 27

anterior auditory cortex

Answer 27

part of the cortex that is close to the front of the brain and is most responsive to pitch

respond to resolved harmonics, but not unresolved harmonics - suggests these areas are involved in pitch perception (bc resolved harmonics are associated with pitch perception)

Question 28

what happens when the outer hair cells are damaged?

Answer 28

loss of hearing sensitivity and loss of sharp frequency tuning - makes it harder to separate out sounds

Question 29

inner hair cell damage

Answer 29

can also cause a loss of sensitivity - inner hair cells can sometimes be lost over an entire region of the cochlea

for both inner and outer - hearing loss occurs for the frequencies corresponding to the frequencies detected by the damaged hair cells

Question 30

presbycusis

Answer 30

a form of sensorineural hearing loss that occurs as a function of age and is usually associated with a decrease in the ability to hear high frequencies

results from the cumulative effects over time of noise exposure, ingestion of drugs that damage the hair cells, and age related degeneration

Question 31

noise induced hearing loss

Answer 31

occurs when loud noises cause degeneration of the hair cells

Question 32

leisure noise

Answer 32

noise associated with leisure activities such as listening to music, hunting, and woodworking - exposure to high levels of leisure for extended periods can cause hearing loss

Question 33

hidden hearing loss

Answer 33

hearing loss that occurs at high sound levels, even though the person’s thresholds, as indicated by the audiogram, are normal

Question 34

audiogram

Answer 34

a plot of hearing loss versus frequency

normal hearing is indicated by a horizontal function at 0dB on the audiogram