Lecture One Flashcards
Rarefaction
The vibrating objects move in, the air molecules move out and fill the space vacated creating a slight decrease in density and pressure.
Condensation
The vibrating object moves out, the nearby air molecules are pushed away and squeezed together creating a slight increase in density of pressure.
What are pressure variations called?
Sound waves; longitudinal waves are waves that transmit wave ossicles backwards and forwards in the direction of the movement of the wave.
What is the speed of sound
330m/s
1500 m/s under water
The stiffer the object the quicker the sound passes through it e.g. 5200m/s for steel but the denser the material the slower the speed because it takes longer to accelerate.
What does the outer ear consist of?
The pinna, concha and ear canel.
Purpose of the pinna
Cause spectral modifications e.g. Filtering the sound of it as it enters the ear. This also helps to determine the location of the sound.
External auditory meatus
The concha that leads to the ear canel which is a short and crooked tube ending at the ear drum (tympanic membrane)
What sound frequencies are we most sensitive to ?
1000 to 6000hz
Describe the middle ear
It’s filled with air and connected to the back of the throats Eustachian tube.
Swallowing and yawning opens the tube and allows the pressure in the middle ear to equalise with external air pressure
Our ears pop because of an imbalance between the two ears.
What does the ossicles do?
Transmit pressure variations in an air filled compartment into pressure variations in a water filled compartment as efficiently as possible.
How do you work out pressure
Pressure - force / area
What acts like a lever system ?
The ossicles act as a lever system turning large, weak vibrations into smaller, stronger vibrations in the oval window.
What does the eardrum do?
The eardrum performs a buckling motion that increase the force of vibration and decreases the displacement and velocity.
What do the ear drums and ossicles collectively do?
They increase the pressure in the oval window to around 20-30 times that act at the ear drum. ( Impedance matching transformer. )
The cochlea
This is where transduction occurs; acoustic vibrations are converted into electrical neural activity.
It’s a fluid filled cavity
Thin tube that’s 3.5cm long and 22mm wide.
Varies along the length of the cochlea being the greatest at the base (near the oval window) and least at the apex.
It’s divided into two tubes
- The basilar membrane
- The resiller membrane
The two membranes create three fluid filled compartments
- The scala vestibuli
- The scala media
- The scala tympani
What are the three bones in the ossicles called
Malleus - hammer
Incus - anvil
Stapes - stirrup
What is loudness?
That attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quite to loud.
Pitch
Is that attribute of auditory sensation in terms of which sounds can be ordered on a musical scale.
Timbre
The attribute of auditory sensation in terms of which listeners can judge that two sounds sound similar presented and having the same loudness and pitch are dissimilar.
Timbe relates to the quality of sound.
What does the cochlea do?
Act as a frequency analyser; convert energy at different frequencies in sound into neural activity in different fibres of the auditory nerve.
What is phase locking
When the response of the neuron is locked to a particular phase of the stimulation. ( a particular phase in the vibration of the basilar membrane)
Johnson 1980
Auditory nerve fibres show a tendency to produce spikes at a particular phase of the sound waveform up to a maximum frequency of about 5000hz.
Temporal code
Is the time between consecutive spikes.
Joris and Yin 1992
Neurons tend to phase lock to the envelope of sound. So they produce spikes at a particular phase of amplitude modulation.
Recap what happens when sound enters the ear.
- Sound enters the ear canal and causes the ear drum to vibrate
- The vibrations are transmitted to the cochlea by the bones in the middle ear.
- Vibrations of the oval window cause pressure changes in the cochlea which cause the basilar membrane to vibrate ( different places on it responding to different frequencies)
- Vibrations on the basilar membrane are detected by the inner hair cells which cause electrical activity (spikes) in the auditory nerve.
Amplitude and Intensity
Subjective experience of loudness
Frequency and Periodicity
Subjective experience of pitch
Quality and Complexity
Subjective experience of timbre
How does sound arise
From the vibration of objects
Pressure waves spread outward from the source of the sound of the listener
Organ of Corti
Embedded in the tectorial membrane are outer hair cells that when bent in a particular direction open ion channels therefore changing the electrical potential and resulting in neural discharge.
How many neurons in the human auditory system?
30,000
