Lecture One

Question 0

Rarefaction

Answer 0

The vibrating objects move in, the air molecules move out and fill the space vacated creating a slight decrease in density and pressure.

Question 1

Condensation

Answer 1

The vibrating object moves out, the nearby air molecules are pushed away and squeezed together creating a slight increase in density of pressure.

Question 2

What are pressure variations called?

Answer 2

Sound waves; longitudinal waves are waves that transmit wave ossicles backwards and forwards in the direction of the movement of the wave.

Question 3

What is the speed of sound

Answer 3

330m/s
1500 m/s under water
The stiffer the object the quicker the sound passes through it e.g. 5200m/s for steel but the denser the material the slower the speed because it takes longer to accelerate.

Question 4

What does the outer ear consist of?

Answer 4

The pinna, concha and ear canel.

Question 5

Purpose of the pinna

Answer 5

Cause spectral modifications e.g. Filtering the sound of it as it enters the ear. This also helps to determine the location of the sound.

Question 6

External auditory meatus

Answer 6

The concha that leads to the ear canel which is a short and crooked tube ending at the ear drum (tympanic membrane)

Question 7

What sound frequencies are we most sensitive to ?

Answer 7

1000 to 6000hz

Question 8

Describe the middle ear

Answer 8

It’s filled with air and connected to the back of the throats Eustachian tube.

Swallowing and yawning opens the tube and allows the pressure in the middle ear to equalise with external air pressure

Our ears pop because of an imbalance between the two ears.

Question 9

What does the ossicles do?

Answer 9

Transmit pressure variations in an air filled compartment into pressure variations in a water filled compartment as efficiently as possible.

Question 10

How do you work out pressure

Answer 10

Pressure - force / area

Question 11

What acts like a lever system ?

Answer 11

The ossicles act as a lever system turning large, weak vibrations into smaller, stronger vibrations in the oval window.

Question 12

What does the eardrum do?

Answer 12

The eardrum performs a buckling motion that increase the force of vibration and decreases the displacement and velocity.

Question 13

What do the ear drums and ossicles collectively do?

Answer 13

They increase the pressure in the oval window to around 20-30 times that act at the ear drum. ( Impedance matching transformer. )

Question 14

The cochlea

Answer 14

This is where transduction occurs; acoustic vibrations are converted into electrical neural activity.

It’s a fluid filled cavity
Thin tube that’s 3.5cm long and 22mm wide.
Varies along the length of the cochlea being the greatest at the base (near the oval window) and least at the apex.

It’s divided into two tubes

1. The basilar membrane
2. The resiller membrane

The two membranes create three fluid filled compartments

1. The scala vestibuli
2. The scala media
3. The scala tympani

Question 15

What are the three bones in the ossicles called

Answer 15

Malleus - hammer
Incus - anvil
Stapes - stirrup

Question 16

What is loudness?

Answer 16

That attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quite to loud.

Question 17

Pitch

Answer 17

Is that attribute of auditory sensation in terms of which sounds can be ordered on a musical scale.

Question 18

Timbre

Answer 18

The attribute of auditory sensation in terms of which listeners can judge that two sounds sound similar presented and having the same loudness and pitch are dissimilar.

Timbe relates to the quality of sound.

Question 19

What does the cochlea do?

Answer 19

Act as a frequency analyser; convert energy at different frequencies in sound into neural activity in different fibres of the auditory nerve.

Question 20

What is phase locking

Answer 20

When the response of the neuron is locked to a particular phase of the stimulation. ( a particular phase in the vibration of the basilar membrane)

Question 21

Johnson 1980

Answer 21

Auditory nerve fibres show a tendency to produce spikes at a particular phase of the sound waveform up to a maximum frequency of about 5000hz.

Question 22

Temporal code

Answer 22

Is the time between consecutive spikes.

Question 23

Joris and Yin 1992

Answer 23

Neurons tend to phase lock to the envelope of sound. So they produce spikes at a particular phase of amplitude modulation.

Question 24

Recap what happens when sound enters the ear.

Answer 24

1. Sound enters the ear canal and causes the ear drum to vibrate
2. The vibrations are transmitted to the cochlea by the bones in the middle ear.
3. Vibrations of the oval window cause pressure changes in the cochlea which cause the basilar membrane to vibrate ( different places on it responding to different frequencies)
4. Vibrations on the basilar membrane are detected by the inner hair cells which cause electrical activity (spikes) in the auditory nerve.

Question 25

Amplitude and Intensity

Answer 25

Subjective experience of loudness

Question 26

Frequency and Periodicity

Answer 26

Subjective experience of pitch

Question 27

Quality and Complexity

Answer 27

Subjective experience of timbre

Question 28

How does sound arise

Answer 28

From the vibration of objects

Pressure waves spread outward from the source of the sound of the listener

Question 29

Organ of Corti

Answer 29

Embedded in the tectorial membrane are outer hair cells that when bent in a particular direction open ion channels therefore changing the electrical potential and resulting in neural discharge.

Question 30

How many neurons in the human auditory system?

Answer 30

30,000