Chapter 11: Audition

Question 1

What do the distal and proximal stimuli refer to?

Answer 1

• Distal - The thing in the world that is capturing your attention
• Proximal - The physical phenomenon that impinges on sensory receptor cells

Question 2

What are longitudinal sound waves?

Answer 2

• Waves that are represented by the compression and rarefaction of air/gas/liquid molecules
• Compression is sometimes referred to as condensation
• The air molecules are not moving, just being displaced (back and forth) for a short period

Question 3

What are the air dynamics for compression and rarefaction?

Answer 3

• Compression: high density, low volume
• Rarefaction: low density, high volume

Question 4

How are pure tones represented?

Answer 4

• Pure tone = a simple sound wave. Can be generated by tuning forks or computers, usually very rare in nature
• Changes in pressure described by a sine wave
• Air pressure found on the y-axis, time found on the x-axis

Question 5

What are the two primary properties found in a simple sound wave?

Answer 5

• Frequency - Number of times per second that the entire pattern of pressure changes. Measured in Hertz. Determines the perception of pitch
• Amplitude - Difference between max and min pressure in a sound wave. Measured in decibels. Determines the perception of loudness

Question 6

What formula relates sound pressure to decibels?

Answer 6

dB = 20xlog(P/P knot)

Question 7

What decibel level is painful? Which one can lead to permanent hearing loss?

Answer 7

• 120 dB is painful
• 130 dB can lead to permanent hearing loss

Question 8

What’s the ratio of increases in decibel levels compare to that of perceived loudness?

Answer 8

• Increases of 10dB are usually perceived as 2x louder.
• Ex. 50 dB is 8x louder than 20dB (2x2x2)
• Only occurs when they’re the same frequencies of sound

Question 9

What are audibility curves?

Answer 9

• Suggests that we can hear some frequencies better than others
• Plot the minimum amplitude required to detect varying frequencies
• Indicate that we are most sensitive between 2000-4000Hz, as these sounds don’t have to be very loud for us to detect them.

Question 10

What are equal-loudness curves?

Answer 10

• Indicate the sound levels (amplitudes) needed to create the same perception of loudness at different frequencies
• The curves are not perfectly parallel to one another

Question 11

What are fundamental frequencies?

Answer 11

• Determine a sound’s pitch
• They are whole number multiples of the following harmonics
• Often represented by the lowest frequency in a complex waveform, which then determines the proceeding intervals for the following overtones.
• “1st harmonic”

Question 12

How are complex tones different from pure tones?

Answer 12

• Pure tone: Simple sound wave. Changes in pressure described by sine wave. Very rare in real life
• Complex tone: Made up of several pure tones added together. Have a much more complex wave form.

Question 13

What’s a Fourier analysis?

Answer 13

• A breakdown of a complex waveform into its constituent pure tones
• Each pure tone has its own frequency and amplitude
• The proceeding harmonics are just whole-number multiples of the fundamental frequency
• Original pitch is always determined by the fundamental frequency

Question 14

What’s the main explanation for differences in timbre? What’s another explanation?

Answer 14

• Mainly associated with differences in the complex waveform, where some harmonics may be absent
• Also associated with an instrument’s attack and decay:
  *Attack = time it takes to reach the max amplitude at the beginning of a tone
  *Decay = the decrease in sound at the end of a tone (eg. a piano has a very rapid attack, while a violin is the opposite)

Question 15

What happens when we remove the fundamental frequency from a tone?

Answer 15

• There’s no change in the perceived pitch since the fundamental frequency is still found in the intervals between each proceeding harmonic
• Often referred to as the “illusion of the missing fundamental”

Question 16

What parts consist of the outer ear?

Answer 16

1)Pinna - Involved in sound localization. Collects sound waves into the ear.
2) Auditory canal - the wax and distance help protect the eardrum and keep the inner ear at a relatively constant temperature compared to the outside world. Also has a resonance effect for certain sound frequencies, helps amplify them
3) Tympanic membrane (‘eardrum’) - Airtight diaphragm that vibrates with any change in air pressure, which is caused by sound waves. Transmits vibrations to the ossicles.

Question 17

What parts consist of the middle ear?

Answer 17

Its role is to separate the outer and inner ear
1) Ossicles - Malleus (‘hammer’), Incus (‘anvil’), Stapes (‘stirrup’). Connect the tympanic membrane to the oval window, also increase the pressure factor onto the oval window by 20x
2) Middle ear muscles - Connected to the ossicles, they help protect our ears from very loud sounds, but not super effective. When they contract, they pull on the ossicles to dampen their movement. Referred to as the acoustic reflex. Better for low-frequency noises
3) Eustachian tube - Connects middle ear to upper throat area. Briefly opened by yawning, swallowing etc. Helps equalize pressure between middle ear and outer ear for the tympanic membrane to be able to vibrate properly

Question 18

Why is it important that the ossicles centralize the force from the tympanic membrane onto the oval window of the cochlea by such a large factor?

Answer 18

• The inner ear is filled with a very dense fluid, so it requires a lot more energy to cause displacements in the fluid found in the cochlea, that’s why the vibrations from the tympanic membrane are centralized onto one area.

Question 19

What are the different parts of the cochlea?

Answer 19

1) Vestibular canal (scala vestibuli) - After the stapes vibrates against the oval window, it causes a wave of pressure through the fluid in this canal
2) Tympanic canal (scala tympani) - Wave of pressure then travels through this canal and presses on the round window (which helps relieve pressure in the cochlea)
3) Cochlear duct (cochlear partition) - Contains basilar membrane and organ of Corti, as well as the tectorial membrane.

Question 20

What’s the basilar membrane?

Answer 20

• Found in the cochlear duct
• Very thin membrane that is found all along the length of the duct
• Thicker, narrower, stiffer near base
• Thinner, wider, more flexible near cochlear apex

Question 21

Where and what’s the purpose of the Organ of Corti?

Answer 21

• Rests on top of the basilar membrane
• Structure responsible for auditory transduction since it contains nerve hair cells
• 3 500 inner nerve hair cells in one row (responsible for auditory transduction
• 12 000 outer nerve hair cells in 3 rows (sharpen the response of the inner hair cells)

Question 22

What are stereocilia?

Answer 22

• 50-150 hair-like projections that are found on the top of all hair cells (hairs on hairs)
• They bend due to vibrations in the cochlear fluid and the movement of the tectorial membrane
• The bending causes the K+ and Ca+ ion channels to open, which causes the nerve hair cells to fire
• The tips of ion channels are linked across multiple stereocilia
• Only works when bending in one direction

Question 23

What’s another name for the cochlear fluid?

Answer 23

• Perilymph

Question 24

What’s frequency theory?

Answer 24

• A valid theory for coding pitch
• The idea that certain frequencies of sound waves cause hair cells to fire at the same frequency
• Phase locking occurs, where the direction of the hair cells are stuck in the same direction due to the linked tips only opening in one direction
• Because of this, info is combined across multiple neurons to account for the rate of high frequency sounds
• This process if often referred to as temporal coding

Question 25

What’s place theory?

Answer 25

• A valid theory for coding pitch
• States that only neurons in a specific portion of the cochlea will fire in response to a specific frequency
• This is due to the varying thickness of the basilar membrane, where some areas will be affected more than others, depending on the frequency
• Waves in the perilymph will elicit a wave-like movement in the basilar membrane
• Each location along the membrane will bend most to sounds of a characteristic frequency
• Different frequencies will also produce specific patterns of displacement, these are called displacement envelopes

Question 26

Why are displacement envelopes important when coding pitch?

Answer 26

• The patterns produced by the displacement envelopes are detected by the auditory cortex
• High frequency = max firing at the base of cochlea (makes sense cause it’s thicker at this spot, so it’s affected by higher vibrations)
• Low frequency = max firing at apex of cochlea (makes sense cause it’s much thinner, doesn’t require super high vibrations)

Question 27

What does it mean to refer to the cochlea as an acoustic prism?

Answer 27

• When it comes to complex tones, the cochlea will break down its constituent pure tones, like a prism and light
• Performs its own Fourier analysis

Question 28

T/F: Place theory is more valid than frequency theory

Answer 28

• FALSE
• Both are correct
• Temporal coding is more useful for pitch perception for sounds with frequencies less than 500Hz. Anything above that, place theory (spatial coding) is more useful

Question 29

What did the DeCasper and Fifer study regarding infant voice recognition discover?

Answer 29

• Newborns could control what they listen to, depending on how they sucked on their soothers (in bursts or pauses)
• At age of 2 days, babies were preferring to listen to recordings of their mother’s voice versus that of a strangers.

Question 30

What did the DeCasper and Spence (1986) study regarding prenatal recording preference discover?

Answer 30

• Babies would listen to recording of their mother’s voice in the womb
• Mother either read a “Cat in the Hat” or “Dog in the Fog” story
• After birth, the baby would prefer the version read to them in the womb
• Also did studies regarding habituation and dishabituation to music they listened to while still in the womb
• Also found changes in heart rate, kicking, depending on hearing voice of mother or someone else