Lecture 5

Question 1

Definition of ‘a sound’

Answer 1

A rhythmic compression of air molecules that propagate as a wave.

Question 2

Definition of ‘compressions’

Answer 2

Regions of high air pressure.

Question 3

Definition of ‘rarefactions’

Answer 3

Regions of low air pressure.

Question 4

Sound has three dimensions

Answer 4

1. Frequency
2. Amplitude
3. Complexity

Question 5

Frequency

Answer 5

Corresponds to our perception of pitch.

• Low frequency - low pitched sound.
• High frequency - high pitched sound.

Question 6

Amplitude

Answer 6

Corresponds to our perception of loudness.

• High amplitude - loud sound.
• Low amplitude - soft sound.
• Usually expressed in decibels.

Question 7

Complexity

Answer 7

Corresponds to our perception of timbre.

• Simple - pure tone.
• Complex - mix of frequencies.

Question 8

Timbre

Answer 8

Arises because of overtones (e.g., multiples of the fundamental frequency.

• Relative strengths of overtones determines tone colour/quality (timbre)

Question 9

Decibels (dB)

Answer 9

The decibel scale is a logarithmic scale that measures the relative strength of a sound compared to a standard sound based on absolute threshold of human hearing.

Question 10

Frequencies heard by an ordinary listened

Answer 10

20 and 20.000 Hz

Question 11

What frequency is the ear most sensitive to?

Answer 11

1000-4000 Hz.

Question 12

Outer & middle ear

Answer 12

The pinna leads sounds through the auditory (ear) canal and to the ear drum (tympanic membrane), that starts vibrating. The vibrations are amplified through three ossicles (ear bones: hammer, anvil, stirrup) in the middle ear and subsequently transferred to the oval window (area behind stirrup).

Question 13

Inner ear

Answer 13

Vibration of the oval window sets the liquid in the cochlea in motion. Hair cells on the basilar membrane (location in the organ of corti) detect this vibration and send impulses to the brain.

Question 14

Frequency theory (temporal coding)

Answer 14

The frequency of a tone is coded in the firing rate of neurons. A tone of 300 Hz thus makes these neurons fire at a rate of 300/s.

• For low tones this is correct.
• Maximum firing rate of neuron is ~1000, while we can hear tones much higher.

Question 15

Place theory (place coding)

Answer 15

Different frequencies activate different regions of the basilar membrane.

Question 16

Tonotopic organisation
What is active, where is it maintained?

Answer 16

Middle and high frequencies are coded via differential activation of the hair cells.

• In response to a complex sound, multiple regions of the membrane vibrate and many nerve cells are simultaneously active.
• Maintained in the primary auditory cortex (A1)

Question 17

Auditory pathway - from cochlea to A1

Answer 17

From the cochlea, information travels to the cochlear nucleus. Most of the axons of the cochlear nucleus cells cross over to the contralateral side of the brain. Both crossed and uncrossed fibres connect to the superior olivary complex. This is the first structure that receives information from both ears. Next stop is the inferior colliculus followed by the medial geniculate body, and finally the auditory cortex.

Question 18

Stereophonic hearing

Answer 18

• Because our ears are on opposite sides of our head.
• Timing and loudness are the most important cues.

Question 19

Interaural difference in timing (ITD)

Answer 19

• For interaural time difference
  Sound arrives sooner in the closest ear.
• Better cue for low frequency tones, as they bend around objects.

Question 20

Interaural difference in loudness (ILD)

Answer 20

• For interaural level difference.
  Sound is louder in the closest ear.
• Best cue for high frequency tones, as sound waves cannot bend around the head so the difference in perceived loudness is maximised.

Question 21

Cone of confusion

Answer 21

For every combination of ITD and ILD cues, there is a cone of confusion - places where sound could have come from.

Question 22

Colliculi superior
what is it and its purpose?

Answer 22

Midbrain structure that is well-known for integrating information from sound, touch, and vision.

• Main purpose is to saccade the eyes to a potentially important location that needs to be checked in the fovea.

Question 23

Ventriloquist effect

Answer 23

When a sound is synchronised with a visual even from a different location, if often appears as if the sound emanates from the visual location.

Question 24

The McGurk effect

Answer 24

Seeing a speaker pronousing a /g/ (visual information) when the speech sound is actually a /b/ (auditory information), listeners will report hearing /d/.

Question 25

Haptic perception

Answer 25

Active exploration of size, contour, texture, and weight of objects.

• Requires integration of motoric and somatosensory senses.

Question 26

Somatosensory senses

Answer 26

Touch receptors have donut-shaped receptive fields.

• There is a contralateral organisation and sensitivity at skin-level as a function of the surface of somatosensory cortex.

Question 27

Gateway theory

Answer 27

Pain arises as a result of activation of particular nerve fibres (a-Delta fibres [initial sharpe pain] and C fibres [dull pain that lasts longer]).
These fibres travel through the (dorsal horn of the) spinal cord, where the signal can be forwarded to the brain or blocked.
A beta fibres that are activated by light touch and pressure also run through the spinal cord and their activation can prevent the pain signal from being forwarded to the brain.

Question 28

Vestibular system

Answer 28

Sense organ in the inner ear.

• Semicircular canals detect head rotations.
• Otoliths detect linear acceleration.
  Canals keep the head straight and are connected to the eyes in order to allow them to fixate and create a stable image. They also maintain balance and update their position relative to gravity.

Question 29

Olfaction (smell)

Answer 29

Odorant molecules present in air molecules bind to receptors in the olfactory epithelium that send information directly (i.e., without crossing hemispheres) to the bulbus olfactorius which connects to areas controlling social and emotional behaviour and memories.

Question 30

Olfactory receptor sensitivity

Answer 30

• They adapt very easily.
• Sensitivity to substances differs between smells and individuals.

Question 31

Gustation

Answer 31

Smell and taste combined define flavour. Taste is primitive.

Question 32

5 qualities of taste

Answer 32

1. Sweet
2. Salty
3. Sour
4. Bitter
5. Umami

Question 33

Papilae

Answer 33

• Visible bumps on tongue

Contains taste buds that have taste receptor cells which connect to the cranial nerve.