Lecture 11 (DONE)

Question 1

Light and Sound both travel through the air as waves but how are they different?

Answer 1

1. Light is measured in wavelengths, while sound is measured in wavelengths per second
2. Light is an electromagnetic phenomenon whereas sound is a mechanical phenomenon.

Question 2

What is the chain of events in the ear?

Answer 2

1) Changes in air pressure (i.e., vibrations) enter the outer ear ->
2) Vibrations on the tympanic membrane ->
3) Vibrations of the ossicles (middle ear) ->
4) Vibrations on the oval window ->
5) Vibrations in the INNER EAR
a) Vibrations in fluid of scala media, basilar membrane
and tectorial membrane ->
b) Movements Of Cilia On Hair Cells->
c) Depolarization Of Hair Cells->
6) Hair cells provide input to Auditory Nerve cells, which provide input (via the 8thCranial
Nerve) to the “Cochlear Nucleus” in Brainstem

Question 3

What is frequency theory?

Answer 3

In frequency theory, the basilar membrane vibrates at the frequency of the sound which leads to auditory neurons producing action potentials at the same frequency.

Question 4

What is place theory?

Answer 4

In Place theory, each part of the basilar membrane is sensitive to a different range of frequencies called a tonotopic map.

Question 5

When do place and frequency theory work together?

Answer 5

Frequency theory and place theory work together, where with sounds under 1000Hz frequency is encoded using frequency theory but sounds greater than 5000Hz place theory is used for encoding. In the frequencies between 1000 and 5000 Hz place theory and frequency theory encoding is done in combination.

Question 6

Reason how the pinna acts to filter frequencies. What kind of location cue can this be?

Answer 6

The different parts of the pinna reflect or absorb certain frequencies, for example the top part of the pinna reflects higher frequencies than the bottom. This can be used as a cue for sounds elevation.

Question 7

Explain the difference between interaural time difference and interaural intensity difference and how they are related.

Answer 7

We use both interaural time differences and interaural intensity difference as cues for a sounds azimuth. Interaural time difference is when a sound arrives at one ear before the other ear.
Interaural intensity difference is when a sound has to go from one ear through the head to the other ear, the sound is attenuated before reaching the other ear creating a ‘sound shadow’.

Question 8

What is sound?

Answer 8

Physical vibration of an object that produces local changes in air pressure

Question 9

How does sound travel within the ear?

Answer 9

Because of these changes in air pressure, it travels as waves, which causes parts of the inner eat to vibrate.

Question 10

At what frequency do human hear?

Answer 10

20-20,000 Hz

Question 11

What are the two types of sound?

Answer 11

Pure and Complex

Question 12

What is a pure tone?

Answer 12

single frequency

Question 13

What is a complex tone?

Answer 13

Many frequencies ex. speech

Question 14

What is the function of the outer ear?

Answer 14

Gathers sound and funnels it into the tympanic membrane (eardrum)

Question 15

What does the middle ear have and what are its functions?

Answer 15

The middle ear contains ossicles. These ossicles serve as mechanical transformers. They transmit pressure signals from one membrane (eardrum) to another (oval window)

Question 16

What does the inner ear contain?

Answer 16

semicircular canals and cochlea

Question 17

What ossicles are in the middle ear?

Answer 17

hammer, anvil, stirrup

Question 18

The hammer connects to the _________, while the stirrup connects to the _________.

Answer 18

eardrum, oval window

Question 19

What is the problem when sound is going through the middle ear?

Answer 19

The sound that comes within the outer ear is just air. The problem is when you go from an air medium to a liquid medium, it gets harder to transmit a pressure signal (b/c water is denser than air).

Question 20

What are the two ways that the middle ear overcomes the problem of sound traveling down to the oval window?

Answer 20

1) The ossicles are arranged in a lever-like way. That helps increase the pressure signal from the tympanic membrane to the oval window.
2) We can decrease the area to increase the pressure signal.

Question 21

What are hair cells?

Answer 21

They are the first neurons in the chain of the auditory pathway.

Question 22

The optic nerve is for vision, while the ________ is for audition

Answer 22

auditory nerve

Question 23

What is the Scala media?

Answer 23

it’s the fluid that’s sitting around the basal membrane

Question 24

What is the purpose of hair cells?

Answer 24

They make connections to the next neuron in the chain

Question 25

What are the chain of events in the ear?

Answer 25

1) vibrations enter the outer ear
2) vibrations on the tympanic membrane
3)vibrations of the ossicles
4)vibrations on the oval window
5)vibrations in the inner ear: a) vibrations in fluid of scala media, basilar membrane, and tectorial membrane b)movement of cilia c)depolarization of hair cells - (they do not require an action potential)
6) hair cells provide input to Auditory nerve cells (which provide input via 8th cranial nerve) to the “cochlear nucleus” in brainstem

Question 26

What are the two theories on how the basilar membrane of your inner ear could encode different pitches of sound?

Answer 26

Frequency Theory and Place Theory

Question 27

Which theory is right for encoding different pitches?

Answer 27

They’re both right. For anything that’s very low freq. sound: <1000Hz, that’s what the frequency theory does. For any high freq. sound >5000Hz, it looks like the place theory. Between these two frequencies, the brain seems to use a combination

Question 28

For the field of audition, what do you call horizontal and vertical?

Answer 28

-Azimuth (horizontal)
-Elevation (vertical)

Question 29

What cues do Humans Use for Evelation?

Answer 29

Monaural cues from the pinna. [in the form of “differential frequency filtering”]

Question 30

What is differential frequency filtering?

Answer 30

It’s similar to how light gets reflected and we see color. (but opposite)

Some frequencies more than others, get absorbed by the pinna of the ear

Question 31

What cues do humans use for Azimuth? (how do we know if sound is coming form the left or right?)

Answer 31

Binaural Cues (comparison between the two ears):
1)Interaural Time Differences (ITD): a sound form the “left” arrives at the left ear earlier than the right ear
2)Interaural Intensity Differences (IID): a sound from the “left” has to go through the head to reach the right ear, and is attenuated in intensity in right ear as compared to left ear