W9 - Ear and Auditory Perception ✅ Flashcards
What causes sound/sound waves?
- Sound wave consists of vibrating particles.
- Cause other particles to vibrate -> sound can travel from the source
- Contains high pressure and low pressure regions.
What are the characteristics of sound wave in relation to how it is perceived?
One cycle of sound wave consists of change in pressure from high (compression) to low (rare fraction) and back again.
Characteristics of sound waves:
- Amplitude (height) = loudness
- Frequency (hertz) = pitch
- Complexity (combination) = timbre (sound quality)
What is sound frequency in human hearing?
- Measured in Hertz: the number of waves per second.
- Higher frequency = shorter wavelength
- Typical human hearing: 20 - 20,000 Hz
- Low frequency (infrasound -> high frequency (ultrasound)
How can we make sense of complex waves?
- Fourier analysis
- Identify fundamental frequency = wavelength of the longest component -> pitch of sound
- Harmonics (smaller but higher in frequency sound waves) -> timbre
What are the main structures of the ear and their functions?
Outer ear: collect sound to ear canal
Middle ear: amplifies and leads sound to eardrum, generating vibrations
- eardrum: vibrates when sound waves hit
- malleus, incus & stapes: connect the eardrum to inner ear, amplifies vibration
Inner ear (cochlea): vibrations from eardrum are converted to electrical signals transmitted to brain for auditory perception
- basal membrane with hair cells: convert movement of fluid to electrical signals
- cochlear duct: vibration from eardrum causes the fluid here to move -> stimulate hair cells
- vestibular system: maintain sense of balance
- tympanic canal & round window: ensure cochlear fluid does not build up pressure, maintain function of cochlea
How does hair cells convert the movement of cochlear fluid to electrical signals?
- When hair bent - trap doors open
- Allow K+ ions to diffuse in and stimulate synaptic vesicles
- Synaptic vesicles release neurotransmitter across synapse
- Cause action potential in ganglion cells
What are meant by tonotopic & tonotopic cortical organisation?
Hair cells
respond
preferentially to
a particular
frequency
Tonotopic organisation is maintained as far as primary
auditory cortex in the temporal lobe
* Neurones next to one another respond to neighbouring
frequencies
How does the vestibular system help with maintaining balance?
Vestibular system structure:
- The vestibular system have three semicircular canals filled with fluid.
- Each canal has a membrane called cupula that contains tiny hair cells that detect movement
Explanation & Process:
- When we turn our head: the fluid in the canal moves causing the cupula to bend/deflect
- Hair cells on cupula also move -> transmit electrical signal to the brain
- Vestibular - ocular reflex: signals cause brain to coordinate eye movement to stabilize vision when our head moves.
What’s the link between pitch and loudness in sound perception?
- Pitch depends on frequency
- Loudness depends on amplitude
Equal loudness curve: Low frequency
sounds need to be more intense to be
perceived as equally loud as higher frequency sound
What’s space perception using sound?
Doppler effect: shift in frequency of the sound wave in relation to movement of the sound source
Binaural space perception: difference in distance of sound wave traveled to the left and right ear allow us to locate the origin of the sound
-> head shadow effect: sound is diffuse around the head before it can travel to the left ear (e.g. if sound source is on the right)
What’s auditory grouping or streaming?
The ability to distinguish between a mixture of sound by grouping similar sounding ones.
Grouped into streams by proximity in:
1. space (same source)
2. time
3. frequency
(4. timbre & pitch)
What is an example of auditory illusion?
Shepard tones: appearance of a continuously ascending scale even though the scale repeats
Explanation: due to ambiguous pitch (mixtures of tones) we interpret them as always being the higher pitch
What is meant by sine-wave speech?
- A way of studying speech
- Using simple tones (sine waves) to represent different speech sounds and removing acoustic cues (pitch, frequency, timbre etc.)
- Knowledge of the sentence helps recognition
