lecture 11 Flashcards
what is sound?
Physical vibration of an object that produces local changes in air pressure, in the form of variations in the concentration of air molecules
These changes in air pressure, which travel as “waves”, enter the outer ear, causing parts of the inner ear to VIBRATE
what phenomenon is sound and light
sound is a mechanical phenomenon
light is an electromagnetic phenomenon
wavelength for sound
(Pure Tone) SOUND: “frequency” = #cycles/sec (or Hz) (e.g., 100 Hz)
how much can humans hear
20 - 20,000Hz
what are the 2 types of tones
(1) Pure tone: single frequency (e.g., 5000 Hz, tuning forks)
(2) Complex tone: many frequencies (e.g., speech)
what happens in the outer ear?
Gathering of sound and funneling to the tympanic membrane -
wall that divides (eardrum)
tympanic membrane = eardrum
what happens in the middle ear?
Ossicles (3 little bones in ear): act as mechanical
transformers,
transmit pressure signal from
one membrane (eardrum) to
another (oval window)
whats the first neuron in auditory system
hair cells
what are the Chain of events in EAR
1) Changes in air pressure (i.e., vibrations) enter the outer ear ->
2) Vibrations on the tympanic membrane (i.e., ear drum)->
3) Vibrations of the ossicles (middle ear) ->
4) Vibrations on the oval window ->
5) Vibrations in the COCHLEA (which is a part of the inner ear)
Vibrations in fluid of scala media, basilar membrane and tectorial membrane ->
Movements of cilia on hair cells ->
Neural signal (mechanotransduction) in hair cells ->
6. Hair cells provide input to auditory cells, which provide input to the cochlear nucleon in brainstem… which provides input to the auditory part of the thalamus, which projects to auditory cortex
what are the 2 theories
Frequency theory: basil membrane vibrates in synchrony with the sound entering the ear, which ultimately leads to producing action potentials in auditory nerve cells at the same frequency
Limitations: max APs/sec = 1000Hz but humans can hear up to 20k Hz
Place theory: each part of the basilar membrane is sensitive (vibrates best) to a different range of sound frequencies (called a tonotopic map)
20000 best vibrate the base of cochlea (stiff)
200 best vibrates the apex (floppy)
Basic answer:
<1000Hz: frequency theory, >5000Hz: place theory
Between these frequencies, use some combination
what are the 2 Auditory Space Perceptions
Azimuth (horizontal)
Elevation (vertical) I
What cues do humans use for elevation (below and above)?
Monaural cue (can use only one ear) from the pinna in the form of differential frequency filtering
What cues do humans use for azimuth?
Binaural cues (comparison between 2 ears)
Interaural time differences:
A sound from the left arrives at the left ear earlier than the right ear
Interaural intensity differences:
A sound from the left has to go through the head to reach the right ear, and is attenuated in intensity in right ear as compared to left ear
explain parts of the pinna absorb vs. reflect different frequencies
Reflected frequencies go into your auditory canal
Some frequencies, more than others, get absorbed (vs. reflected into the auditory canal) by the pinna of the ear (high frequencies get reflected to the auditory canal and low frequencies get absorbed by pinna)
