Perception - Loudness and Pitch

Question 1

What is the perceptual definition of sound?

Answer 1

Sound if the experience we have when we hear

Question 2

What is the physical definition of sound?

Answer 2

Sound is pressure changes in air or other medium caused by the vibration of an object

Question 3

What is a pure tone?

Answer 3

Simplest type

Occurs when changes in air pressure form perfect sinusoidal wave

Question 4

What are the characteristics of pure tones?

Answer 4

Amplitude

Frequency

Question 5

What is amplitude?

Answer 5

How much difference between increases and decreases in pressure

Size of variation in air pressure

Difference between peak and trough

Question 6

What is amplitude related to?

Answer 6

Perception of loudness

Question 7

What is frequency?

Answer 7

How many cycles of decreases and increases in pressure travel past a certain point in a second

Number of cycles per second

Question 8

What is frequency measured in?

Answer 8

Hertz (1 Hz = 1 cycle)

Question 9

What is frequency related to?

Answer 9

Perception of pitch

Question 10

What are complex sounds?

Answer 10

Made up of lots of different frequencies of sound mixed together

All sound waves can be described as some combination of sine waves

Question 11

What do natural sounds consist of?

Answer 11

Fundamental frequency superimposed by additional waveforms with higher frequencies (the harmonics)

Question 12

What is a fundamental frequency?

Answer 12

Lowest, most dominant frequency

Question 13

What is the ear divided into?

Answer 13

Three sub-divisions = outer, middle and inner ear

Question 14

What are the features of the outer ear?

Answer 14

Pinnae

Auditory canal

Tympanic membrane (ear drum)

Question 15

What is the pinnae?

Answer 15

Visible external parts of the ear

Question 16

What is the function of the pinnae?

Answer 16

Capture sound waves and direct down ear (auditory) canals

Question 17

What is the auditory canal?

Answer 17

~3cm tube-like structure

Question 18

What is the function of the auditory canal?

Answer 18

Protects middle ear

Question 19

What is the tympanic membrane (ear drum)?

Answer 19

Cone-shaped membrane separating outer and middle ear

Question 20

What is the function of the tympanic membrane (ear drum)?

Answer 20

Sound waves induce difference in pressure either side of tympanic membrane, causing it to vibrate

Larger amplitude sounds result in larger vibrations

Higher frequency sounds result in faster vibrations

Question 21

What are the features of the middle ear?

Answer 21

Small cavity (~2 cubic cm) containing ossicles (smallest bones in the human body)

Question 22

What are the ossicles?

Answer 22

Malleus (hammer)

Incus (anvil)

Stapes (stirrup)

Question 23

What is the function of the ossicles?

Answer 23

Bones amplify vibrations of tympanic membrane and transmit to inner ear at oval window

Question 24

What are the features of the inner ear?

Answer 24

Main structure is cochlea (snail-like liquid-filled organ)

Basilar membrane

Question 25

What are the features of the cochlea?

Answer 25

Three parallel canals - vestibular, middle, tympanic

Question 26

What is the basilar membrane?

Answer 26

Separates middle and tympanic canals

Question 27

What is the function of the inner ear?

Answer 27

Vibration of oval window displaces fluid in cochlea, resulting in change of pressure which moves up and down spiral structure Auditory transduction triggered by motion of basilar membrane Pressure waves in cochlea causing basilar membrane to move

Question 28

What is auditory transduction?

Answer 28

Motion of basilar membrane translated into neural signals by structures in Organ of Corti, which extends along its surface Voltage generated when specialised hair cells contained within Organ of Corti bent Produces impulses in auditory nerve cells which are sent to brain Hair cells extremely sensitive - overstimulation by loud sounds can damage hair cells and lead to hearing loss

Question 29

How are sound levels measured to describe differences in amplitude?

Answer 29

In decibels Logarithmic scale Change of 20dB corresponds to ten-fold increase in amplitude

Question 30

What is rate code?

Answer 30

Sound amplitude coded in the firing range of auditory nerve fibres Responses increase with increasing sound intensity

Question 31

How does a high amplitude affect the rate code?

Answer 31

High amplitude High firing rate High rate code

Question 32

How does the rate code allow us to discriminate loudness across a range of sound levels?

Answer 32

Some fibres have high spontaneous rates and saturate rapidly while others have low spontaneous rates and saturate slowly

Question 33

Are amplitude and loudness directly proportional?

Answer 33

No For sound to be perceived as twice as loud, amplitude needs to be increased by factor of ~3.16 (10dB)

Question 34

Does loudness depend on frequency?

Answer 34

Yes Auditory systems not equally sensitive to all sound frequency

Question 35

If the frequency is higher, is the pitch higher or lower?

Answer 35

Higher

Question 36

What is the lowest and highest frequencies that a human can hear?

Answer 36

Lowest = 20Hz (below can feel the sound) Highest = 20,000Hz (20kHz)

Question 37

What are the two ways to code frequency?

Answer 37

Place code Timing code

Question 38

What is the place code?

Answer 38

Different auditory nerve fibres respond to different frequencies Sound frequencies causes vibration in specific areas along the basilar membrane

Question 39

Where do low frequencies cause vibrations in the basilar membrane?

Answer 39

Near apex

Question 40

Where do high frequencies cause vibrations in the basilar membrane?

Answer 40

Near base

Question 41

What is the timing code?

Answer 41

Not only which auditory nerve fibres respond but when they respond Hair cells respond in little packets of firing, not all the time Auditory nerve responses synchronised to changes in pressure - property called phase-locking Occurs up to frequencies of about 400Hz (lower frequencies)

Question 42

What has been suggested by experiments using electrical stimulation via cochlea implants?

Answer 42

Both place and timing of stimulation affect perception of pitch

Question 43

Why does the same note sound different on different instruments?

Answer 43

Pitch determined primarily by fundamental frequency of sound Instruments have same fundamental frequencies but different harmonics Number, frequency ratios and relative amplitudes of the harmonics dictate the quality or timbre of sound

Question 44

What is the missing fundamental illusion?

Answer 44

Continue to perceive pitch consistent with missing fundamental frequency Pitch isn't simply determined by cochlea, brain infers missing fundamental from harmonics