Audition Flashcards
Which stimulus is used for audition?
Sound waves
What are sound waves?
Pressure waves travelling through any medium that will allow their conduction
What are the two key characteristics of sound waves?
Frequency
Amplitude
What is frequency?
The number of sound waves (or cycles) per second
What is frequency measured in?
Hertz
What does frequency determine?
The pitch of a sound - high frequencies produce high-pitched sounds and low frequencies produce low-pitched sounds
What is the full range of frequencies than humans can detect?
20 to 20,000 Hz
What is amplitude?
The vertical size of sound waves
What is amplitude measured in?
Decibels - the measure of the physical pressure occurring at the eardrum
What does amplitude determine?
The loudness of a sound - smaller waves are quieter, larger sound waves are louder
What is considered a safe level in decibels?
85 and below
What is the minimum threshold of hearing?
0 decibels
Give an example of a sound at 0 decibels
A fly at 3m away
Give an example of a sound at 50 decibels
A busy restaurant
What is the level of decibels that can cause damage with prolonged exposure?
90 decibels
Give an example of a sound at 90 decibels
A kitchen blender
What is the human pain threshold for hearing?
130 decibels
Give an example of a sound at 130 decibels
A loud metal workshop
What is the threshold for potential immediate damage to hearing?
140 decibels
Give an example of a sound at 140 decibels
A jet fighter taking off 25m away
What does the outer ear consist of?
Pinnae
Auditory canal
Eardrum
What are pinnae?
The visible parts of the ears which reside outside of the head
What is the function of the pinnae?
To collect sound and help localise where sounds are coming from
Which frequencies are the pinnae particularly good at collecting?
Frequencies within the human speech range
What happens once a sound is detected by the pinnae?
It is funnelled, amplified and directed into the auditory canal
What happens after sounds reach the auditory canal?
They travel to the eardrum, which vibrates in response
What does the middle ear consist of?
Three bones - the ossicles
What are the names of the ossicles?
Hammer
Anvil
Stirrup
What are the roles of the ossicles?
Protecting the inner ear from damage
Impedance matching - matching the impedance of the air to that of the cochlea
What is impedance?
How much a given medium impedes sound waves
Give examples of different mediums and their impedance
Concrete - high
Pillows - moderate
Water - moderate to low
Air - very low
Inner ear - extremely low
What is the danger caused by the inner ear’s low impedance?
Loud sounds can damage the inner ear
What does the inner ear consist of?
The cochlea
What is the cochlea?
A coiled, fluid-filled tube
What is the basilar membrane?
A sheet of tissue that runs the length of the cochlea
What is the organ of Corti?
An organ that contains thousands of tiny sound receptors (hair cells)
Where is the organ of Corti located?
On the basilar membrane
What happens once a sound reaches the inner ear?
Pressure is created at the oval window (by vibrations of the ossicles) and this causes the cochlea to be in motion
What happens once the cochlea is in motion?
The waves of fluid within the cochlea cause the basilar membrane to vibrate, meaning that the hair cells in the organ of Corti bend
What happens once the hair cells in the organ of Corti bend?
They fire an action potential, triggering the release of neurotransmitters, and the nerve impulses are then sent to the brain via the auditory nerve and the thalamus
Which part of the brain are nerve impulses concerning sound sent to?
The auditory cortex
What do the feature detectors in the auditory cortex respond to?
The frequency and amplitude of sounds
What are the two pieces of information the brain uses to code loudness?
Higher amplitude sound waves cause hair cells to bend more, which releases more neurotransmitters, causing the auditory nerves to fire more frequently
Certain hair cells also have higher thresholds than others, so only bend at louder sounds
What are the two theories of how the brain codes pitch?
Frequency theory
Place theory
What is frequency theory of pitch perception?
The nerve impulses that are sent to the brain match the frequency of the sound wave, e.g. if a sound is at 30HZ, then 30 nerve impulses are sent to the brain
What is the problem with frequency theory of pitch perception?
It only works for sounds up to 1000Hz because there is an upper limit to the frequency of nerve impulses that can be generated - the nerves cannot fire fast enough to match the frequency
What is place theory of pitch perception?
The specific point within the cochlea where the wave of fluid peaks (and bends the hair cells most strongly) serves as information for frequency coding
Where does the wave of fluid peak for high frequency sounds?
Close to the oval window - the lower the frequency of the sound, the further from the oval window the wave peaks
Which theory of pitch perception is correct?
Both are correct, but only place theory can account for sounds at all frequencies
What characteristics of sound does the nervous system use to localise sounds?
The time the sound arrives at both pinnae
The intensity differences of the sound in each pinnae
Which ear will perceive the sound first and loudest?
The closest ear
What is another factor that influences sound localisation and how?
Elevation - this tells the brain whether the sound is coming from high up or down low
How do we know that everyone’s sound localisation is individualised?
There have been experiments where moulds of different people’s pinnae were given to others, and the results showed that when they were “wearing other people’s ears” their localisation abilities were worse
However, we can adapt to different pinnae over time to improve these abilities again
What are the two types of hearing loss?
Conductive hearing loss
Sensorineural hearing loss
What is conductive hearing loss?
Hearing loss that comes from problems with the mechanical system that transmits sound waves to the cochlea
Which specific structures are often damaged in conductive hearing loss?
The eardrum and the ossicles
What potential solutions are there for conductive hearing loss?
Hearing aids - they increase the amplitude or frequency of the sound to allow them to reach the inner ear
The ossicles could also be surgically repaired
What is sensorineural hearing loss?
Hearing loss caused by damaged receptors within the inner ear, or damage to the auditory nerve itself
Why can sensorineural hearing loss not be fixed with hearing aids?
The hair cells in the ear do not regenerate after damage, and so even if the amplitude of sounds are increase, the hair cells still cannot detect the sounds
What are the common causes of damage to the inner ear?
Ageing
Disease
Loud sounds
What are sensory prosthetic devices?
They provide sensory input that can substitute for what cannot be supplied by the person’s sensory receptors
What concept is are sensory prosthetic devices based on?
The idea that we do not hear with our ears, but instead with our brains
How do cochlear implants work?
Electrodes are placed into the cochlea, and sounds are gathered by a microphone - the information is then mechanically broken down into frequency and amplitude, which is translated into nerve impulses that get sent straight to the brain, bypassing any damaged structures
What does the evidence suggest about cochlear implants?
It suggests that they do work, but it takes time to adjust to the implant as the sounds are not the same as they were before the hearing damage
Research on congenital deafness also suggests that the earlier children are given implants, the higher the chance they have to learn how to successfully use them and the better their hearing will be
What is the controversy surrounding cochlear implants?
They take away the need to learn sign language and so they can reduce the sense of community among deaf people
