Hearing Flashcards
What will an oscillating object cause the air to do?
become more and less dense = compression and rarefaction
What are radiating waves?
sound waves that come outwards from the source
How do you calculate wavelength?
velocity divided by frequency
How do you define amplitude?
Measured in decibels
Mechanism for describing the intensity of sound
Amplitude is generally expressed as a ratio
What is the range of human hearing? and what happens to this as you get older?
freq = 20-20 000 Hz
As you get older your high end range gets affected and becomes lower
amplitude - 0-140 dB
Sometimes sound pressure levels are adjusted using “A weighting”. what does this do? how will a high freq sound then compare to a low freq sound that are the same volumes?
Down-scales low frequencies to acknowledge our lower sensitivity
A higher freq sound will appear louder than the low freq sounds due to us being more sensitive to the higher frequency sound
Explain the role of the tuning curve
- this is for the auditory nerve fibres
For any given auditory nerve cell, it has a preferential frequency to activate the cell
What is the role of the ossicles (bones in the middle ear)
- Tympanic membrane deflects
- Middle ear bones move
- Membrane in oval window moves
- Basilar membrane moves
- Round window - allows fluid to move back and forth
What does the middle ear do?
acts as a lever
it converts high amp & low force motion to the ear drum into low amp & high force motion at the oval window
what is the stapedius reflex and what do they do?
- 2 muscles that act on the ossicles
- the contraction of these muscles pulls stapes away from the oval window. this decreases the transmission of vibrational energy to the cochlea . Stapedius reflex occurs in response to very loud sounds.
Also occurs during speech
Crucial for preventing hearing damage
What is the cochlea made up of?
round window
3 scalae –> 1. Scala vestibulae 2. Scala media 3. Scala tympani
Helicotrema
what is the organ of corti? where is it in the cochlea?
it is embedded in the Basilar membrane in between the scala vestibulae and the scala tympani
it has inner hair cells sensation and outer hair cells motors (presin - a protein that is capable of contracting)
how are the hair cells of the organ of corti activated?
Small up-down movements of the basilar membrane cause a large relative shear of the tectorial membrane, thus activating the hair cells and causing hyper or hypo polarisation depending on which way it is going.
How does you ear distinguish between different frequencies of sound?
- Pitch place theory
2. The ear is a fourier analyser
Explain the pitch place theory
different freqs of sound will be coded at different places along the basilar membrane in the cochlea. it will cause vibrations at certain points
- high frequency= oscillations at the lower end of the cochlea where the membrane is tort and stiff.
- low frequency - oscillations at the other end of the cochlea where the membrane is more loose
- Different frequencies of sounds are coded by different neurons along the auditory nerve
Explain how the ear is a fourier analyser
any waveform can be decomposed into sine waves of various frequencies
even a square wave can be made up of sine waves: combine the fundamental frequency with progressively smaller harmonics
where does amplification happen in the ear?
the active outer hair cells by positive feedback
outer hair cells can generate sound
otoacousitic emissions are echos in response to clicks delivered to the ear.
Absence of this indicates a problem of the inner ear. therefore this is used to assess hearing in newborns
It is also a possible mechanism for some types of tinnitus.
hearing is most sensitive to which frequencies?
Speech freqs
which are at 400-3000 Hz
What is noise induced hearing loss that is:
1. Temporary
2. Permanent
called?
- Temporary Notch. Anything over 85 dB is potentially damaging
- Permanent sensorineural defect
What is the auditory pathway in the brain?
Sound activates many areas from the cochlear nerve to the auditory cortex. It also includes the superior olive (brainstem)
Why is it important to localise sounds?
- To know where other player are on the pitch and where to pass to etc
What is the cocktail party effect?
we can understand conversation from an individual speaking among many others. It involves localisation cues as well as vision.
Judging distance. High frequency sounds travel less well; far away sounds are dominated by bass.
Expectations eg intensity of voice
Relative attenuation of certain types of sound… what travels best? worst?
Echoes give us lots of cues
Bass travels best
sibilants travel worst
What are the 3 techniques in which we judge direction?
- inter arual timing / phase differences
- Inter-aural volume differences
- Spectral colouring by the pinna & head
Explain the concept of Interaural time delay (ITD).
How accurate is this?
a click from the left will arrive at the left ear before the right ear.
It is accurate to one degree
what is jeffress theory of ITD detection?
Neurons in the superior olive act as coincidence detectors.
When action potentials arrive simultaneously from both ears, MSO neuron is more likely to fire.
It relies on differing lengths of axons.
provides a neuronal map of sound location
When would you use inter-aural phase differences?
If sound is a continuous tone, you use phase difference to localise it. Its not very useful when the wavelength is shorter than the head (ie a high frequency sound)
Explain how inter-aural volume differences works
the head provides a sound shadow. Reduces volume in the ear opposite the sound source.
There is greater reduction for high frequency sounds, hence far away speech is more bassy.
explain the role of spectral colouring by the pinna and head
The pinna (outer ear) reduces sounds from certain directions and amplifies sound from other.
Invisible to low frequency sounds (bass)
Therefore, the spectral content of sound combined with prior experience, can be used for localisation.
Why does head size matter?
big head = large left/right time difference. small head = not so much.
BIg heads will use timing inter-aural differences. Small heads will use loudness differences.
Smaller heads are better at detecting high frequency sounds
Explain the role of the cone of confusion
sounds coming from 2 different places can produce identical interaural level differences (ILD) and ITD (timing) profiles and the 2 ears.
- eg sounds coming from behind the head can sometimes seem like they’re coming from in front.
- Tilting and turning the head alters the cone of confusion
What are the auditory time reaction values?
140-160 ms
sound takes 3ms per metre
What is the startle response? Whats it evoked by?
Evoked by loud sounds at about 120 dB
evokes a blink at 40ms and a neck contraction at 80ms.
It is too fast to involve the cerebral cortex. and is mediated by the brainstem
