Chapter 10 - Audition

Question 1

sound waves

Answer 1

sound is generated when air is vibrated. small variations in air pressure then occur. sound waves are a mechanical displacement of molecules by a change in pressure that possesses the physical properties of frequency, amplitude, and complexity.

Question 2

frequency

Answer 2

is measured in Hertz (vibrations per second). we hear this as pitch

Question 3

amplitude

Answer 3

measured in decibels. we hear this as loudness

Question 4

complexity

Answer 4

lies in the fact that most sounds are a combination of different frequencies and amplitudes. we hear this as timbre

Question 5

fundamental frequency

Answer 5

is the rate at which the complex waveform pattern repeats. key feature of complex tones is periodicity (fundamental frequency repeats at regular intervals; aperiodic sounds = noise)

Question 6

overtones

Answer 6

higher-frequency sound waves that vibrate at whole-number multiple of the fundamental frequency

Question 7

outer ear

Answer 7

consists of the auricle (pinna) which absorbs sounds from the outside, and the outer ear canal, which is closed off by the eardrum. the eardrum vibrates when it is struck by sound waves

Question 8

middle ear

Answer 8

from the eardrum, the vibration is transmitted to the three ossicles; hammer, anvil, and stirrup. these offer protection against loud noises and distort sound a little. they transmit the vibration to the oval window

Question 9

inner ear

Answer 9

the oval window is an opening in the cochlea. this is where the receptor cells are located. the hollow cochlea is filled with lymphatic fluid (cochlear fluid). a second window allows the cochlear fluid to vibrate inside the cochlea when activated by vibrations in the oval window. in the middle of the cochlea is the organ of corti, which includes the basilar membrane. hair cells are specialized neurons with cilia on top. the outer hair cells are attached to the tectorial membrane, whereas the inner hair cells only touch it loosely

Question 10

transduction of sound waves into neural impulses

Answer 10

organ of corti in the inner ear converts sound waves into neural activity. when the vibrations in the oval window cause the cochlear fluid to move, the basilar and tectorial membranes bend, causing the fluid to flow past the inner hair cells.

Question 11

excitation

Answer 11

when the cilia bend in one direction, there is depolarization of the membrane, excitation: the firing rate increases, and K+ and Ca2+ influx

Question 12

inhibition

Answer 12

when the cilia bend in the other direction, there is hyperpolarization of the membrane: the firing rate decreases, and K+ efflux

Question 13

auditory nerve

Answer 13

the axons of the inner hair cells form the auditory nerve, which sends auditory information from the ear to the brain. Inner hair cells are the actual auditory receptors, if they become damaged, there is permanent hearing loss and constant leakage of calcium.

Question 14

tonotopic organization

Answer 14

hair cells in the cochlea code sound frequencies as a function of their location on the basilar membrane. different frequencies are encoded at different locations, allowing us to distinguish between pitches

Question 15

beginning of the cochlea (base)

Answer 15

the basilar membrane is thick, narrow and stiff. here the hair cells mainly react to high frequencies (up to 20000 Hz)

Question 16

end of the cochlea (apex)

Answer 16

the basilar membrane is thin, wide, and soft. here the hair cells react to low frequencies (from 20 Hz)

Question 17

exception in tonotopic organization

Answer 17

sounds below 200 Hz are coded temporality, this means that the sound frequency equals the firing rate of neurons

Question 18

coding of amplitude (loudness)

Answer 18

another example of temporal coding, larger amplitudes in sound waves correspond to more intense vibration in the oval window, cochlear fluid, and basilar and tectorial membranes.

Question 19

coding of location

Answer 19

two factors come into play:
- interaural time difference: difference in arrival time between left and right ear
- interaural intensity difference: difference in sound intensity between left and right ear
allow us to localize sound on the horizontal plane

Question 20

the auditory pathway to the cortex

Answer 20

the auditory nerve leaves the cochlea and enters the brainstem at the level of the medulla, connecting with the cochlear nucleus. projections from the cochlear nucleus connect with both contralateral and ipsilateral cells in the superior olivary complex and trapezoid body. the cochlear nucleus and the superior olivary complex send projections to the inferior colliculus in the midbrain. from here, information is sent to the contralateral and ipsilateral medial geniculate nuclei in the thalamus (= relayed station for sensory information). the medial geniculate nuclei then send the information to the higher cortical areas in the cortex. auditory input from the two ears is therefore mixed in the brain to form a unified auditory perception.

Question 21

auditory cortex

Answer 21

divided into a primary auditory cortex (A1) and a secondary auditory cortex (A2, planum temporale). the auditory ventral stream reaches A1 and is linked to the sound recognition (“what” stream). the auditory dorsal stream reaches A2 and directs movements based on sounds (“how” stream)

Question 22

lateralization

Answer 22

is the localization of function primarily on one side of the brain. it is important to note that the other hemisphere also contributed to these broad functions

Question 23

wernicke’s model

Answer 23

distinguished between language comprehension and language production. for right handed individuals, language comprehension is in the left temporal lobe in Wernicke’s area.

Question 24

wernicke’s aphasia

Answer 24

damage to wernicke’s area causes wernicke’s aphasia (sensory aphasia). you have difficulty understanding what other people say, and while your speech is fluent, it is incoherent and makes no sense.

Question 25

broca’s aphasia

Answer 25

damage to broca’s area causes broca’s aphasia (motor aphasia). you can understand what other people are saying but you have trouble speaking. language production is in the left frontal lobe in broca’s area.

Question 26

organisation of music

Answer 26

similar to that of language, but lateralized to the right hemisphere instead of the left hemisphere.