Week 2: Auditory Perception

Question 1

Amplitude

Answer 1

How high are the sound waves (sine waves) - how much are the air molecules pushed together and pulled apart.
Measured in decibels (dB) and corresponds to loudness of the sound.

Question 2

Auditory Filter

Answer 2

Blocks certain frequencies in a complex sound.

Question 3

Auditory Nerve Fibres

Answer 3

Nerve endings that connect to inner hair cells - these transmit the electrical impulses to the auditory nerve and to the brain.

Question 4

Decibels

Answer 4

Unit of measure for amplitude, or loudness.

Question 5

Band Pass Filter

Answer 5

Blocks sound components of frequencies outside a pre-determined range.

Question 6

Frequency

Answer 6

How many sound waves (cycles of compression and rarefaction) in a full second, measured in Hertz (Hz). Corresponds to the pitch of the sound.

Question 7

Basilar Membrane

Answer 7

Membrane that divides the cochlea into 2. It contains ~3500 inner hair cells, and carries vibrations (sound energy) along its length.

Question 8

Harmonic Series

Answer 8

Components of sound that have a frequency that is an integer multiple of the fundamental frequency.

Question 9

Characteristic Frequency

Answer 9

Inner hair cells respond best to certain frequencies, determined by the part of the basilar membrane to which they are connected.

Question 10

Cochlea

Answer 10

The organ in the inner ear that transduces sound into electrical energy. Essentially a small coiled tube filled with fluid.

Question 11

Phase

Answer 11

Defines a particular point on a waveform. Measured in degrees and corresponds to changes to the perceived quality of the sound (timbre).

Question 12

Pitch

Answer 12

How high or low the sound is. Corresponds to the frequency of the sound.

Question 13

Rarefaction

Answer 13

Part of a sound wave, where air molecules are stretched apart.
Corresponds to the negative cycle of a sound wave (sine wave).

Question 14

Sine Wave

Answer 14

Description of the waveform for a pure time. Sound waves (a graphical representation of pressure changes over time) are in the shape of a sine wave.

Question 15

Timbre

Answer 15

The quality of a sound. Corresponds to the phase of a sound.

Question 16

Dynamic Range

Answer 16

Difference between the minimum sound pressure level (intensity) to which a nerve fibre responds, and the intensity at the fibre’s maximum firing rate.
Individual auditory nerve fibres have a dynamic range of only 20-60dB.

Question 17

Low Pass Filter

Answer 17

A filter that blocks sounds above a certain frequency.

Question 18

Spectrogram

Answer 18

A graphical representation of changes in the frequency content of a signal over time - visual depiction of a Fourier Analysis (a decomposition of complex sounds).

Question 19

Frequency Code

Answer 19

Inner hair cell impulses are timed to coincide with a certain phase of the wave (“phase locking”), at least for low frequencies. This is so that the response rate of a particular nerve fibre should reflect the frequency (pitch) of the signal.

Question 20

Inner Hair Cells

Answer 20

Located in the basilar membrane (in the cochlea). These cells have several protruding “hairs”.
The vibrations in the basilar membrane caused by fluid displacement (caused by sound waves) deflect these hairs, which generates electrical impulse and is transmitted to auditory nerve fibres.

Question 21

Meatus

Answer 21

The passage leading to the ear (ear canal).

Question 22

Ossicles

Answer 22

The 3 small bones of the middle ear. Transmit sound energy from the eardrum to the oval window in the inner ear.

Question 23

High Pass Filter

Answer 23

Blocks sound components under a certain frequency (lets higher frequencies through).

Question 24

Pinna

Answer 24

The external (visible) part of the ear. Focuses sound waves into the ear.

Question 25

Inner Hair Cells

Answer 25

Located in the cochlea. These cells have several protruding “hairs” which touch the basilar membrane.
The vibrations in the basilar membrane caused by fluid displacement (caused by sound waves) deflect these hairs, which generates electrical impulse and is transmitted to auditory nerve fibres.

Question 26

Ossicles

Answer 26

The 3 small bones of the middle ear. Transmit sound energy from the eardrum to the oval window in the inner ear (malleus, incus & stapes).

Question 27

Phase Locking

Answer 27

A neuron’s ability to fire its action potential at the same phase of each (sound) wave, so that the firing/response rate reflects the frequency of the sound.

Question 28

Place Code

Answer 28

Hair cells have a “characteristic frequency” to which they respond best, determined by the part of the basilar membrane to which they are connected.

Question 29

Waveform

Answer 29

Sound (compression and rarefaction of air molecules) can be mapped using a graph of pressure changes over time.

Question 30

Loudness

Answer 30

Intensity of a sound signal, corresponds to the amplitude of the sound wave.

Question 31

Tonotopic Organisation

Answer 31

Specific areas of the basilar membrane move in response to different frequencies.