Week 5 - Hearing & Sound

Question 1

Define Amplitude

Answer 1

Amplitude = loudness of a sound. How high a wave goes. When we say high, it actually means being pushed further away from you.

Question 2

Define Frequency?

Answer 2

Frequency = pitch. How many cycles a wave goes through in a unit of time.

Question 3

Define Phase?

Answer 3

Phase - position within a cycle. Peaks on the sound wave

Question 4

Define Sine Wave

Answer 4

Sine wave = pure tone. The simplest sound wave.

Question 5

What is the range of human hearing?

Answer 5

20- 20 000 HZ

Question 6

What is a pure tone?

Answer 6

A pure tone is essentially 1 frequency. However, real sounds in the environment are a combination of many frequencies & amplitudes.

Question 7

What is Fourier Analysis?

Answer 7

Decomposing complex sounds into their sine waves

Question 8

What is a Fundamental?

Answer 8

Fundamental = lowest frequency component of a complex sound. Adding harmonics together in a sound wave. Sound waves are composed of fundamentals and their harmonics.

Question 9

What are the biological parts of the outer-ear?

Answer 9

Pinna
External Auditory Canal
Eardrum (tympanic membrane)

Question 10

What does the Pinna do, and where is it located?

Answer 10

Pinna = increases the sound amplitude (crack around edge of your outer ear). Important in catching sound waves. Helps determine direction from which a sound is coming. The pinna can distinguish front/ back.

Question 11

What is the external auditory canal and where is it located?

Answer 11

External auditory canal = the outer-ear. provides protection, increases sound amplitude. Right before the eardrum. Pressure increases and sound needs to travel through your small ear canal.

Question 12

What is the Eardrum (tympanic membrane) and where is it located?

Answer 12

Eardrum = in outer ear. Vibrates in response to sound waves. First point of contact, moves bones in middle ear and transports throughout ear structure.

Question 13

What are the parts on the Middle Ear?

Answer 13

Ossicles (collectively):
- Malleus
- Incus
- Stapes

Smallest bones in the human body. They transmit the vibration of the eardrum into the cochlea. Further amplifies sound and provides protection against high amplitude sounds at the same time.

Question 14

What parts are in the Inner Ear?

Answer 14

Cochlea = contains auditory sensory receptors. Oval window/ spiral part of the inner ear.
- Starts vibration of the eardrum, transmitted to oval window where the cochlea is.
- 3 canals in cochlea separated by membranes.
~ Reissner’s membrane, Basilar membrane, (on which auditory receptor cells/ hair cells, converts vibrations into neural signals in the cochlea duct).
~ Physical waves in external environment need to be converted into neural signals - the cochlea is where this occurs.

Question 15

Central Auditory Pathways. What are the different parts involved?

Answer 15

Nerve fibres from each cochlea synapse in a number of sites on the way to the primary auditory cortex:
~ cochlea nucleus
~ Superior olivary nucleus
~ inferior colliculus
~ Medial geniculate nucleus

Signal arriving at cochlea nucleus splits & goes to each of the superior olivary nuclei 0 beyond this point input from both ears is present in both hemispheres. Beyond the point of the cochlea nucleus, the auditory information splits and involves both sides of the head (two ears).

Cortex is central. Studies reveal tasks which cannot be performed without the cortex: duration of sounds, tones of sounds (REFER TO SLIDES)

Question 16

What is the Basilar Membrane?

Answer 16

Basilar membrane has a unique shape - narrow and stiffer at base, wider at apex. travelling waves move along the basilar membrane & peak at different points, depending on the frequency of the sound.

Each hair cell has its own preferred frequency.

Base of membrane = higher. frequency
Apex of membrane = lower frequency

Question 17

What are tonotopic maps?

Answer 17

Tonotopic maps = present in the auditory system. Organisation is seen repeatedly in the auditory pathways - auditory neurons are arranged in an orderly matter.

Primary visual neurons in primary visual cortex are organised in an orderly matter. Not according to spatial location, but according to frequencies of the sound (tonotopic map).

Question 18

Pitch perception: does one ear do all the work, or do we require two?

Answer 18

Perception of a missing fundamental = when high-order harmonics are present in the absence of the fundamental (first harmonic), the missing fundamental is ‘filled in’

A missing fundamental is perceived even when harmonics are presented to different ears.

Question 19

What do you know about loudness perception?

Answer 19

Loudness perception = how strongly hair cells fire & overall firing rates.
Sound duration - longer = louder

The important factor here is frequency (higher = louder sound). E..g lower sounds (lower frequency) quieter.

Question 20

Describe what is involved in auditory space perception:

Answer 20

You try to determine a sounds:
~ horizontal direction (azimuth)
~ vertical direction
~ distance

Vision provides more precise information about an object’s location. Nothing on basilar membrane directly indicates sound locations.

Question 21

What is auditory space perception classified as?

Answer 21

A binaural process;
- Interaural time difference (onset difference & phase difference)
- Interaural intensity difference

Question 22

What is Interaural Time difference?

Answer 22

When sound reaches two ears at different times (unless directly in front of behind you - which is onset differnce)

Question 23

What is onset difference?

Answer 23

Detected by “delay line”

Question 24

What is the role of head movements?

Answer 24

Head movements are generally helpful for auditory localisation.
By changing the position of the ears, you can experience changes in interaural time/ intensity differences.

Question 25

Explain a little bit about Horizontal VS Vertical direction?

Answer 25

humans perceive horizontal directions better than vertical directions through auditory cues

• Pinnae are more effective in distinguishing front/back than above/ below
• Ear positions can be varied more freely along the horizontal direction

Question 26

What are some limits of auditory localisation?

Answer 26

Most of the auditory localisation cues are dependent on the distance between a sound source and ears. As a result, it is difficult to distinguish locations of sounds that are equidistant to an ear - cone of confusion

Question 27

What are the (2) cues for auditory distance perception?

Answer 27

Loudness
Energy ratio of direct & reverberant sound