Hearing Flashcards
What is the definition of sound?
Pressure waves in the are producing by a vibrating object, which are detected by the auditory system
What is the distal stimulus of sound?
Vibrating object
What is the proximal stimulus of sound?
Pattern of kinetic energy at the eardrum
What is the phase?
Point along the wave measured in degrees
What is the perceptual counterpart to phase?
There is no direct perceptual counterpart
What is the amplitude?
The displacement of a wave from peak to trough
For large ranges, a logarithmic scale is easier to work with
What is the frequency?
The number of sound wave cycles per second in Hz
What is loudness?
The perceptual experience of sound intensity
Related to amplitude and sound pressure
What is 1 sone of loudness?
100 Hz pure tone at 40 dB
How do we double loudness?
Increase dB by 10 dB
What is pitch?
Quality of sound ranging from low to high; allows sounds to be ordered on a musical scale
Associated with frequency
Short duration will be heard as a click
What is the fundamental frequency?
Lowest frequency in a Fourier spectrum of complex sound wave
What are harmonics?
Components of a complex sound having frequencies that are multiples of the fundamental
The number and amplitude of harmonics contribute to the timbre of a sound
What is timbre?
Character or nature of a sound
Due to different frequency components produced by a vibrating source stimulus
What is the audibility curve?
Describes the absolute threshold for hearing each different frequency
What is the auditory response area?
The dynamic range of intensities from threshold to pain
What is the equal loudness curve?
Graph of decibel levels of various frequencies that seem equally loud
How do we determine the equal loudness curve?
Present standard: 1000 Hz tone at a certain dB level
Adjust intensity of other frequencies to match loudness of standard
What is the equal loudness curve also affected by?
Auditory adaptation
Auditory fatigue
What is auditory adaptation?
Same sound seems softer if presented for a long time
What is auditory fatigue?
Temporary hearing loss due to high intensity sounds
What is the pinna?
The ear on the side of your head
Channels certain sound waves into the ear canal
What is the external auditory meatus?
The ear canal
Protects the middle and inner ears
Amplifies frequencies 2000 to 5000 Hz via resonance
What is the tympanic membrane?
The eardrum
Struck by sound waves and vibrates
Transmits sound to structures in the middle ear
What are the ossicles?
Malleus, incus, stapes; supported by middle-ear muscles
Concentrates vibration of the eardrum to the oval window
Increases pressure by a 20:1 ratio
Acts as levels, increasing vibration
What is the eustachian tube?
Equalizes middle ear pressure with outside
What are the semicircular canals?
Snail-shaped structure, filled with cochlear fluid, divided into canals
-Scala vestibuli
-Scala tympani
-Scala media
What is the scala media formed by?
Basilar membrane and Reissner’s membrane
What is the tectorial membrane?
Overhangs the basilar membrane, contains 15000 hair cells
What are the number of inner hair cells?
3000
What is the cell alignment of inner hair cells?
1 row
What is the cilia number of inner hair cells?
40-60/cell
What is the cilia alignment of inner hair cells?
Straight lines
What is the function of inner hair cells?
Sensory
What is the number of outer hair cells?
12000
What is the cell arrangement of outer hair cells?
3-5 rows
What is the cilia number of outer hair cells?
100-120/cell
What is the cilia alignment of outer hair cells?
V or W shaped
What is the function of outer hair cells?
Supportive
What are spatial ganglion cells?
30000 nerve fibers
95% are type 1 = inner hair cell, large, myelinated
5% are type 2 = outer hair cells, small, slow
What is the transduction of sound waves like?
Vibration -> eardrum -> ossicles -> oval window -> vestibular canal/cochlear partition -> basilar membrane
How do the basilar and tectorial membranes move with respect to each other?
Laterally
What does the shearing force do?
Bends the cilia of outer hair cells, which are embedded in the tectorial membrane
How are the cilia of inner hair cells bent?
By fluid flow
What links the tips of cilia?
Actin fibers
What happens when the cilia of inner hair cells bend?
Actin stretches and opens a trap door, allowing K+ ions into the hair cell which initiates neural signaling by releasing glutamate
What is tonotopic organization?
Neurons activated by similar frequencies are found close to each other
What percent of neurons respond to noise, clicks, and bangs?
40%
What percent of neurons respond to a certain frequency?
60%
What is place code?
The activity of specific neurons encodes different frequencies
What is resonance theory?
Basilar membrane appeared to be composed of transverse fibers
Sounds make fibre vibrate like a harp-string
Each fibre activated by a certain frequency
What is the problem with resonance theory?
The basilar membrane is all connected, no independent stringlike fibres
What is the traveling wave?
The entire membrane vibrates
The basilar membrane differs in elasticity down its length
-narrow/stiff at base
-wide/floppy at helicotrema
Each frequency has its own point of maximum displacement along the membrane
-high frequencies at the base
-low frequencies at the apex
What is the evidence for traveling wave theory?
Observation
Many auditory neurons display frequency tuning curve, responsive to a narrow range of frequencies
Tonotopic organization
Stimulation deafness experiments
Motile response
Masking experiments
What is the point of greatest sensitivity?
Characteristic frequency
What is cochlear amplification?
Outer hair cells sharpen wave around the peak by tilting and changing length
What is tonotopic organization?
Nerve fibres coming from the base are tuned to high frequencies
Those from the apex are tuned to low frequencies
What are stimulation deafness experiments?
High intensity sounds damage parts of the organ of Corti
Damage depends on what frequency was played
What is motile response?
Pattern of vibration on the basilar membrane is narrower than what Bekesy found
Active process sharpens waves
What is two-tone suppression?
Present tone at characteristic frequency of a neuron
Turn on another tone, close in frequency to the other
Neuron’s response rate decreases
Due to outer hair cells affecting movement of basilar membrane
What are masking experiments?
One sound prevents us from hearing another
Masking increases as masker and target frequencies become closer
Making is asymmetrical = target frequencies higher than masker are more affected than frequencies lower than masker
What is perceptual coding?
When we reduce audio file size by removing frequencies that would’ve been masked anyways
What is periodicity pitch?
The case of the missing fundamental
How is periodicity pitch a problem for place coding?
Region on basilar membrane is not moving, so how is pitch corresponding to that location heard?
What is temporal code?
The timing of neural activity encodes different frequencies
What is frequency theory?
Entire basilar membrane vibrates in synch with frequency
Assumed that each vibration produced one action potential in all receptors
What are the problems with frequency theory?
Only part of the membrane moves
There is a refractory period for hair cells
What is the volley principle?
Groups of neurons fire alternately in volleys, some fire while others are refractory
What is phase locking?
Neuron firing is synchronized with the peak of a pure tone stimulus
Does not work well with high frequencies, better with low frequencies
What is tinnitus?
Ringing in the ears, or experiencing a sound when none is present
What is tinnitus commonly caused by?
Loud sounds, drugs, ear infections, food allergies
What are the current theories of tinnitus?
Destroying hair cells causes the brain to remap areas previously served by the destroyed hair cells, resulting in abnormal brain activity
Due to decreased incoming stimulation, there is less inhibition in the auditory cortex, resulting in ore excitatory activity and phantom sound
What is presbycusis?
Age-related hearing loss, due to the degeneration of hair cells and cilia
More likely to occur with increasing age
Higher frequencies are more attenuated with age
