Lecture 6 - Hearing

Question 1

What is sound?

Answer 1

• when a tuning fork is tapped it creates sound waves
• sound waves are changes in air pressure caused by vibrating air molecules
• the energy of the sound waves decreases with the distance from the source
• however no sound is perceived unless someone is there to convert the sound waves into electrical signals

Question 2

What are the 2 basic features of sound waves?

Answer 2

1. frequency (pitch)
2. amplitude (loudness)

Question 3

What is frequency?

Answer 3

• the rate at which air molecules vibrate
• slow vibrations generate low frequency sound waves and are perceived as having low pitch
• high frequency sound waves are caused by fast vibrations and have a high pitch

Question 4

What is amplitude?

Answer 4

• the no. of air molecules that are vibrating in a sound wave
• an increased no. of vibrating air molecules increases the amount of energy in a sound wave which makes the sound seem louder

Question 5

The complexity of sound?

Answer 5

• most sounds = a mixture of frequencies
• the particular mixture determines the sounds complexity

Question 6

How do we capture sound waves?

Answer 6

• the outer ear (pinna) collects and amplifies sound waves
• the middle ear (ear drum) transmits this sound energy mechanically to the fluid filled inner ear
• the inner ear (cochlea) converts these mechanical vibrations into electrical signals

Question 7

How does the ear determine what frequency the sound is?

Answer 7

• the cochlea contains auditory receptor neurons
• these are found next to the basilar membrane
• these receptor neurons convert sound into electrical signals
• different parts of the basilar membrane vibrate at different frequencies of sound

Question 8

How are sound waves converted into electrical signals?

Answer 8

• Auditory receptor cells (hair cells) have hairs that are attached to the basilar membrane of the cochlea and vibrate if the appropriate frequency is heard
• Vibrations of these hairs result in the physical opening and closing of ion channels
• Hearing loss can occur from damage to these hairs

Question 9

Auditory pathways?

Answer 9

• amplitude is denoted by frequency of action potentials
• receptor neurons send their axons to regions of the brainstem
• these signals are then relayed to the midbrain, thalamus and primary cortex in the temporal lobe

Question 10

What is the audible spectrum for humans?

Answer 10

it ranges from 20-20,000 Hz

Question 11

How do we detect where a sound is?

Answer 11

• sound localisation results from integrating information from the 2 ears
• sounds that originate on the left side of the body reach the left ear before the right ear and will also be louder in the left ear
• these differences are not interpreted as 2 different sounds but as 1 sound coming from a specific location
• these differences are detected by neurons in the brainstem and midbrain

Question 12

How do we determine what a sound is?

Answer 12

• neurons in the primary auditory cortex respond to different frequencies of sound
• neurons that respond to high frequency tones are grouped together and neurons that respond to low frequency tones are grouped together

Question 13

What is aphasia?

Answer 13

inability to understand or produce language caused by damage to language regions of the brain

Question 14

What is Wernicke’s aphasia?

Answer 14

an inability to understand or produce meaningful language even though the production of words is intact

Question 15

What is Broca’s aphasia?

Answer 15

the inability to speak fluently despite the presence of normal comprehension and intact vocal mechanisms

Question 16

What hemisphere is language localised in?

Answer 16

the left hemisphere

Question 17

What does the right hemisphere do?

Answer 17

• makes some contribution to understanding the emotional context in language
• also plays an important role in processing music