Hearing

Question 1

What is the physics of air?

Answer 1

Sound is like a way pushed by air. We detect the air pressure wave and then decipher its qualities through amplitude, frequency and phase.

Question 2

What is amplitude?

Answer 2

It is a quality of sound measured in decibels related to loudness.

Question 3

What is frequency?

Answer 3

It is a quality of sound measured in Hz, it is closely related to pitch.

Question 4

What is phase?

Answer 4

It is a quality of sounds related to the position within a cycle of sound.

Question 5

What is the simplest form of sound?

Answer 5

A sine wave. The values of a sine wave help us to understand a sound’s location, determined by degrees. It is an air pressure wave meaning air is being pushed and pulled.

Question 6

How do humans perceive frequency?

Answer 6

We are able to hear within the auditory spectrum of 20 - 20000hz. As frequency goes up, we experience higher frequencies which correspond to pitch. The natural world is full of complex frequencies that we are hearing at once, the ear deconstructs these frequencies by breaking them into their purest tone.

Question 7

What is the lowest frequency component of a sound?

Answer 7

The fundamental.

Question 8

What are harmonics?

Answer 8

They are integer multiples of the fundamental frequency of a sound.

e.g. fundamental = 400hz, harmonics = 800hz, 1200hz, 1600hz etc.

Question 9

What is dissonance in the environment?

Answer 9

Most sounds are made up of a fundamental and its harmonics, when a harmonic is not a multiple of the fundamental we perceive this as a dissonant sound. This is easily detectable by the ear.

Question 10

In the outer ear, what does the pinna do?

Answer 10

It increases the sound amplitude.

Helps determine the direction from which a sound is coming

Can help distinguish between front and back, allowing us to localise sound

Question 11

In the outer ear, what is the external auditory canal?

Answer 11

Provides protection

Increases sound amplitude

The outer environment is much larger than the canal, and thus amplifies the sound to a large extent.

Question 12

In the out ear, what is the tympanic membrane in the eardrum?

Answer 12

It vibrates in response to sound waves

Moves bones in the middle ear

Question 13

What are the three bones in the auditory ossicles inside of the middle ear, and what is its job?

Answer 13

The Three smallest bones in the human body are.

Malleus
Incus
Stapes

The auditory ossicles transmit sounds from the air to the fluid-filled cochlea via lever action.

Question 14

What do the three bones in the cochlea do?

Answer 14

They amply sound and provide the ear with protection against extremely high amplitude.

Question 15

What do the muscles attached to the middle ear do?

Answer 15

These muscles constrict or retract in response to the amplitude of an incoming sound in order to protect the ear.

Question 16

What is the cochlea?

Answer 16

The small snail structure of the ear. It contains auditory neurons, the oval window is the entrance to the cochlea, and air pressure moves in this window which helps sound be translated.

Question 17

What is the oval window?

Answer 17

The membrane covering the opening in the cochlea. the stapes are attached directly to the oval window (this is where vibrations get into the cochlea)

Question 18

What are the three canals in the cochlea and what are they responsible for?

Answer 18

Vestibular canal
Tympanic canal
Cochlear duct

They vibrate in response to the vibrations of the oval window

Question 19

How does a sound pressure wave turn into an audio signal we can hear?

Answer 19

Vibrations from the air are converted when hair cells vibrate in the basilar membrane in the cochlea, and when hair cells vibrate auditory neurons convert the sound into neural signals. Air pushes the caps off of fibre-connecting hairs flooding the transmitter with potassium causing an action potential, they synapse onto auditory nerves which we perceive as frequency.

Question 20

What are the three canals (Vestibular canal, Tympanic canal & cochlear duct) separated by?

Answer 20

The Reisners membrane
Basilar membrane (where the auditory receptor cells are located- in the cochlear duct)

Question 21

How is binaural signal processing achieved in the brain?

Answer 21

Initially, a signal will come into one ear. Once it arrives at the cochlear nucleus it splits and goes to each of the olivary nuclei. Beyond this point, input from both ears is present in both hemispheres.

Question 22

Before sound reaches the auditory cortex, what is processed?

Answer 22

The onset of sound
Changes in sound intensity
Changes in sound frequency

Question 23

What tasks cannot be performed without the auditory cortex?

Answer 23

Discriminating the pattern of several tones
Discriminating the duration of sounds
Localising sounds in space

Question 24

What is the difference between the auditory cortex and the lower structures of the signal chain?

Answer 24

The cortex deals with more complex auditory tasks while the lower structure deals with simple aspects of sound.

Question 25

How does the auditory system isolate and identify frequencies and their components?

Answer 25

Aspects of the basilar membrane are responsible for understanding these frequencies, it is to do with shape and stiffness. At its base it is narrow and moving towards its apex becomes wider. Moving towards its apex it becomes stiffer, frequencies are topographically mapped across the membrane with higher frequencies at the base and lower frequencies at the apex. When auditory neurons enter the membrane there will be different peaks across the membrane that indicate what frequency is being heard.

By finding the peaks in the basilar membrane, we are able to understand the component parts of the sound we are listening to.

Question 26

How does the brain register frequencies (hair cells)?

Answer 26

Each hair cell is localised across the basilar membrane to a particular frequency. When sound entires the membrane, the hair cell will peak and the brain will register that frequency.

Question 27

Frequencies are mapped across the brain, what is the organisation called?

Answer 27

Neurons are organised tonotopically, therefore it is a tonotopic map.

Question 28

What is the missing fundamental when percieving pitch?

Answer 28

When higher-order harmonics are present in the absence of the fundamental (first harmonic), the missing fundamental is “filled in’

Question 29

In pitch perception, what is binaural encoding and why is it important?

Answer 29

This is where structures beyond the cochlear nucleus are contributing to pitch perception. If we are perceiving two different pitches in either ear, binaural encoding is where these sounds are integrated.

Question 30

What are the two basic mechanisms of loudness perception?

Answer 30

Overall firing rates
More neurons fire when a sound is more intense

Range of firing
Each neuron fires more vigorously - wider means louder

Question 31

What are some qualities of loudness perception?

Answer 31

Generally, high-frequency sounds are perceived to be louder (up to 5000 hz) - around 3000-5000hz are perceived to be louder.

As the amplitude goes up, the effect of frequency becomes smaller.

Question 32

In auditory space perception, what are the three aspects of space you are trying to determine?

Answer 32

The sound’s horizontal direction (azimuth)
Vertical direction or location
Distance to the source sound

Question 33

The basilar membrane can only understand what frequencies are in the environment; What are the two ques that can help us localise sound?

Answer 33

Interaural time difference (Onset and phase difference)

Interaural intensity difference

Question 34

What is the interaural time onset difference, and how is it detected?

Answer 34

Unless a sound is in front of or behind you, it reaches two ears at different times. Therefore, this allows you to understand where the sound source is relative to this time difference. It can be detected by a “delay line” mechanism in the brain.

Question 35

In interaural time differences, what is the phase difference and how does it work?

Answer 35

The same sound will most likely be in different phases when it reaches each of the two ears. Meaning the brain can utilise phase information to find out information about the sound. This is useful for low-frequency sounds and not so much for high-frequency.

Question 36

In interaural intensity differences, what happens to the ear that is closer to the sound source?

Answer 36

A sound should be more intense at an ear that is closer to the sound source. The energy of a sound decreases as it travels. The head works as a barrier that reduces the intensity of the sounds called a sound shadow.

Question 37

What is the difference between interaural time difference and interaural density difference?

Answer 37

Interaural time difference is useful for localising low-frequency sounds and interaural intensity difference is useful for localising high-frequency sounds.

Question 38

In auditory localisation, what is the role of head movements?

Answer 38

By changing the position of the ears, you can experience changes in interaural time/intensity differences.

Question 39

When trying to localise sound, what are humans more capable of doing to find this sound?

Answer 39

They can move their heads horizontally, this is far more effective than vertically. The axis of the head is able to move the pinnae to localise the sound in an easier way than moving the entire body.

Question 40

What are some limits of auditory localisation?

Answer 40

As most cues are dependent on the distance between a sound source and ears, it is difficult to distinguish locations of sounds equidistant to an ear i.e. the cone of confusion