Sound and the ear Flashcards
1
Q
What is the environmental stimulus of sound?
A
sound wave
2
Q
What is a sound wave comprised of?
A
compression (high density of air molecules) and rarefaction (low density of air molecules)
3
Q
What is the perceptual phenomenon of frequency, amplitude and complexity of sound waves?
A
- Frequency: pitch
- Amplitude: loudness
- Complexity: timbre
4
Q
What is the frequency?
A
- Measured in Hertz
- number of waves that happen per second
- Higher frequency – shorter wavelength
- Low frequency – longer wavelength
- Typical human hearing range: 20-20,000 Hz
- Middle C on a piano = 261.63 Hz
5
Q
What is amplitude?
A
- High amplitude – low sound
- Decibel scale (logarithmic scale)
- 0 – threshold of hearing
- 20 – country at night
- 140 – threshold of pain
- 180 – spacecraft launch
- Computer produces very straight wave which is why it sounds artificial
- Complex waves = this is what you have in real life
- Expensive musical instruments have nicer waves
6
Q
What is the Fourier analysis?
A
- Fundamental frequency is the wavelength of the longest component this determines the pitch of the sound
- The harmonics determine the timbre, the sound quality
7
Q
What is the structure of the ear and sound (outer section to ear drum)?
A
- Outer ear – acts to channel sound waves into our auditory canal, shaped to catch the sound waves, also protects the auditory canal
- Sound waves travel along the auditory canal to the ear drum
- The ear drum is a membrane that is stretched and the vibrations of the air molecules against it cause the ear drum to begin vibrating
- The pressure of the sound waves is converted into mechanical motion with the ear drum
8
Q
How does the vestibular system work?
A
- involved in balance
- Semi-circular canals (3 within each ear)
Contain a liquid called Endolymph
Deflects a flap of tissue called the Cupula when Endolymph moves
When Cupula is deflected it sends a signal to the brain letting us know the head/body is being moved around
After you have stopped spinning you may get an illusion of turning as the Endolymph is still turning (same happens with alcohol – sets up endolymph circuits) - Vestibular-ocular reflex: we can keep our eyes still when we move
9
Q
How does sound travel through the middle and inner ear?
A
- Ear drum is attached to three small bones (ossicles): the malleus, incus and the Stapes
- The malleus is attached to ear drum. When ear drum moves the malleus moves and transfers the vibrations to the other bones, this causes the vibration of the oval window
- The oval window starts to move and this causes the liquid inside the cochlear to move. This causes the movement of the Basilar membrane
10
Q
Apart from through the ear how else can sound waves get to the ear and what is this useful with?
A
- Sound waves can also get to the ear by bone conduction through the skull – this is why our voice sounds different to ourselves compared to others
- Bone conductors can be used as a hearing aid for people who have conductive hearing loss (problem with hearing within the ear drum and ossicles)
11
Q
What happens with the sound wave in the Basilar membrane?
A
- Basilar membrane runs all the way through the cochlear
- Oval window causes a wave along the basilar membrane
- Our ear is a frequency analyser – shape of sound waves determines the shape of the wave in the basilar membrane
- High frequency causes deflection in earlier portion of basilar membrane
- Hair cells in the organ of Corti detect vibrations in the basilar membrane and then transmit information up to the CNS via the auditory nerve. Hair cells are in the cochlear
- Hair cells change their firing rate when they are bent (deflection of hair cells)
- Hair cells are very sensitive – can detect deflections as small as 10 picometres
- Hair cells are tonotopic: hair cells respond preferentially to a particular frequency (this differs from the visual system which is retinotopic)
12
Q
How does auditory transduction work?
A
- Air pressure changes (kinetic)
- Vibration of eardrum -> middle ear -> oval window (mechanical)
- Cochlear fluid flows (kinetic)
- Hair cells bend (mechanical)
- Auditory nerve fires (neural)
13
Q
Give features of pitch and loudness and auditory perception
A
- Pitch depends on frequency
- Loudness depends on amplitude
- But they are not independent
- More intense low frequency sounds are perceived as lower pitch
- Perception of loudness affected by frequency
- Equal loudness curve: low frequency sounds need to be more intense to be perceived as equally loud.
14
Q
Give features of auditory space perception
A
- Different to perception of space in vision
- Like depth perception in vision (indirect)
- Monaural (one ear)
Loudness (a loud sound is likely to be nearer)
Doppler effect (higher frequency sounds tend to be lost over long distances) - Binaural space perception
Needed to perceive direction
If something is directly in-front of us it will reach the two ears at the same time
Interaural intensity differences – up to 0.07 seconds, e.g. sound coming from right side will reach right ear first
Head movements – can perceive vertical location of sound source
15
Q
What is auditory grouping/ streaming?
A
- Like figure ground separation in vision
- Grouped into streams by proximity (closeness) in space, time and frequency
- If two musicians are on either side of the room it will be easier to tell who is playing what
- Harder to differentiate two voices at the same pitches
