Flashcards in Auditory Deck (72):
What is psychoacoustics?
What we actually perceive (compared to the physiology or physics of sound)
What are the four PHYSICAL properties of waves and sound waves?
What are the physiological characteristics of a wave?
Loudness and pitch
What is waveform?
The amplitude of pressure plotted against time
What is the phase of a wave?
How the wave occurs compared to other waves. They can be "in phase" or "out of phase" depending on their temporal beginning or starting amplitude
What is amplitude?
How is it measured?
The pressure intensity and different in the sound wave (dynes/cm2)
It is measured using the decibel scale
What is the equation for the decibel scale?
P is the current amplitude of pressure
Po is a "reference pressure" which is the human threshold for pressure at the most sensitive region of the spectrum
What is reference pressure?
What is the range of Hz you would find it in?
The threshold for pressure at the most sensitive region of the spectrum (1000-4000hz)
For our purposes, this value is 0.0002 dynes/cm2
So we can say .0002 is equal to 0dB
By what amount do the decibels increase if you increase the sound intensity by one log?
How many decibels is :
1. Threshold (0.0002)
2.Leaves rustling (0.002)
3. Speech (.2)
4. Rock concert (200)
5. Ruptured eardrum (20,000)
4. 120dB (threshold for feeling)
What is the frequency of a waveform?
The higher the frequency, the _________ the wavelength.
Cycles per second (Hz)
The higher the frequency, the shorter the wavelength
What is the difference between the physiological concept of sound and the physical concept of sound?
Physiological is what we perceive based on how the sensory organs and brain manipulate the "physical data"
Physical properties are actual innate properties or the wave
What is the relationship between loudness and intensity?
Is loudness a physiological property or physical?
Why is this relationship this way?
Loudness is a physiological property.
It does NOT have a 1:1 relationship with intensity (amplitude~physical property)
If you increase the amplitude (intensity) by 10dynes/cm2, you will increase the decibels by 20, but the loudness will only increase 2.5-4 fold instead of by a factor of 10.
Physiology condenses the physics scale for us to be able to handle it.
What is the relationship between loudness and frequency?
At what frequencies are we most acute?
We have a frequency dependent threshold where we are most acute between 1000-5000 Hz.
This is the normal range for a human voice so we are esp. Acute at interpreting speech.
What two things do our discriminative ability (resolve power) depend on?
Frequency and intensity (amplitude)
At low and high frequencies, what do you need to do to hear the sound at the same loudness?
Turn up the intensity (increase the wave amplitude)
What is the relationship between pitch and frequency?
A two-fold increase in pitch increases frequency by 3-fold
What is the relationship between pitch and amplitude?
A 4% decrease in pitch will occur of the intensity is increased from 40-110dB.
Pitch decreases as intensity increase (but it takes a HUGE change in intensity for only a slight change in pitch)
Is pitch more dependent on frequency or amplitude?
Pitch is more dependent on frequency. Pitch increases 2-fold for a 3- fold increase in frequency.
Pitch only reduces by 4% for a similar (3-fold) increase in amplitude.
What is sound localization?
Our ability to localize a sound utilizing temporal (phase) and intensity (amplitude) cues
Ex. If the sound is coming from the right, it will hit our right ear before our left ear. The waves will be out of phase so we will know the sound is coming from the right.
What are the structures of the outer ear?
What is their joint function?
Pinna and concha act as resonators to amplify the sound by 10dB (half and order or magnitude)
This only works between the frequencies of 2000 and 5000 Hz
What is the major function of the head and Pinna working together?
At what frequencies/wavelengths does this work?
They block sounds by casting a "shadow" to give intensity differences for spatial resolution
This works only for high frequency tones (kHz) where the wavelengths are less then the width of the head
What is the boundary between the outer and middle ear?
Tympanic membrane (eardrum)
What are the three bones of the middle ear?
What are their two major functions?
Malleus, incus, stapes
1. Transfer sound from a low (air) to high (fluid) imprudence medium. Sound bounces off when you go from air to fluid (mom yelling at you when you're in the pool, but once the sound wave is in the medium it travels faster)
2. Amplification of sound by focusing the force on the tympanic membrane (large diameter) to the oval window (small diameter). This gives a 17x amplification. Level action of the bones increases the amplification by 1.3x
What are the two ways the middle ear increases the amplitude of the sound?
1. Focusing the force from a large diameter (tympanic membrane) onto a small diameter (oval window) --> 17x increase in amp
2. Lever action of the bones --> 1.3x increase in amp
What are the two major muscles of the inner ear and what are their function?
Tensor tympani and stapedius contract to decrease the response to a loud stimuli by reducing transduction during constant loud situations. They are not as effective with acute sounds
What is the tensor tympani attached to?
What is its function and how does it achieve it?
In response to constant loud sound, it will contract to increase stiffness of the tympanic membrane so it can't vibrate as much and transfer as much of the sound.
To what bone is the stapedius attached?
What is its function and how does it achieve it?
With loud constant sound It contracts to retract the stapes from the oval window so it can't transmit the sound from the low to high impedance medium
What is the eustachian tube?
A tube below the bones of the middle ear that connect the ear to the pharynx.
Pressure differences or fluid blockage can cause pain and difficulty hearing.
What is the main structure of the inner ear?
What are the three chambers?
The three chambers are:
1. Scala vestibuli
2. Scala tympani
3. Scala media
What is the entrance to the cochlea?
What is the apex that divides the cochlea?
1. Oval window
Where is the organ of corti located?
What two membranes does it sit between?
What is the function?
The organ if corti is located at the base of the scala media.
It contains structures from the tectorial and basilar membranes.
This is where hair cells sense mechanical forces
The tectorial membrane serves what purpose?
It sits above hair cells in the organ of corti and contributes to shearing action to help the ear sense mechanical forces.
What are the two kinds of hair cells and how many rows of each are there?
What is the function of each type?
Inner hair cells - 1 row that receives 95% of afferent fibers to the ear)
Outer hair cells - 3 rows that serve as efferent fibers to modulate and make areas more or less sensitive
What structure is at the apex of the hair cells?
What are the connections between these structures called?
What is the function?
Stereocilia make connections called tip links that amplify the forces in the area of the molecular sensors.
What is an otoacoustical emission?
If you put a microphone to the eardrum, you can monitor a response after briefly presenting a tone. You will hear efferent sound from the outer hair cells
In what direction would a wave travel with a compression force?
What direction would rarefaction occur?
Compression on the oval window travels through scala vestibuli around the helicotrema, down the scala tympani to the round window
Rarefaction travels from the round window to the oval window because it creates a vacuum pulling stapes
What are the two major functions of the outer hair cell?
1. Sharpen frequency
2. Dampen loud sounds by changing shape and size dependency on depolarization (they can jump up to stiffen and inhibit the basilar membrane)
In the hair cell, what is the concentration of potassium? What does this mean for excitation/inhibition?
At the apex of the hair cell (toward the Stereocilia and tip links) there is Higher K+ outside of the cell so it will flow IN and depolarize.
At the base of the hair cell (near the nerve endings/synapse) there is low K+ outside the cell so K+ flows out and hyperpolarizes.
What stimulates the hair cell?
Shearing forces between the tectorial and basilar membranes
What initiates the auditory nerve action potentials?
The mechanical displacement of hair cell cilia which modulates neurotransmitter release to the nerves.
Why does the apical portion of the hair cell depolarize?
The apical portion of the hair cell is surrounded by high potassium endolymph (+80mV)
The opening of mechanosensitive receptors allow K+ to flow in, depolarizing the cell.
What solution bathes the apical portion of hair cells?
The basilar portion?
1. Endolymph (high K+)
2. Perilymph (low K+)
What is the process of hair cell transmission of sound starting with mechanical shearing?
1. Mechanical shearing btw tectorial and basilar membrane displace cilia
2. Mechanosensitive channels open
3. Because endolymph is high K+, potassium flows in and depolarized
4. Depolarization opens Ca channels at basal end of hair cell
5. Vesicle release occurs and Ca dependent K+ channels open at basal end of cell
6. K+ flows out of the cell at the base because the Perilymph surrounding it has low potassium
7. The cell is repolarized
Why are the hair cells able to "keep up" at low frequency sounds but not high frequency sounds?
There is phase locking at low frequencies.
At higher frequencies (above 1000Hz) phase locking can no longer occur because the neuron refractory period is about 1000Hz
What is phase-locking?
The synchronous firing of auditory neurons with the sound wave
1:1 sound wave to neuronal firing
What is the volley theory?
Encoding pitch at low frequency - the ability of the hair cell system to keep up at low frequencies
What is tonotopic encoding?
Place or label-line encoding.
Compression hits the tympanic membrane, stapes hits oval window, compression travels around helicotrema to round window. The basilar membrane is flexible and supports the traveling wave.
Rarefaction pulls the stapes and fluid travels back toward the oval window.
Compression/rarefaction on the organ of corti cause basilar membrane vibration.
The basilar membrane is thicker and wider the further from the oval and round windows you move so different frequencies will vibrate at different places along the basilar membrane.
High frequency will stimulate hair cells closer to the base (round and oval window) and medium frequencies will stimulate the apex (helicotrema)
How does the thickness and width of the basilar membrane change throughout the cochlea?
It gets wider and and thicker the further it is from the round and oval windows (base)
Hair cells at the base of the basilar membrane Respond to _________frequency stimulation than hair cells closer to the apex.
What is meant by characteristic frequency?
Individual nerve fibers have specific frequencies they are most sensitive to as a result of tonotopic encoding.
Hirt cells from a specific region of the basilar membrane will be more tuned to frequencies where that region vibrates.
How do cochlear implants work?
How is this different from hearing aids?
They utilize the tonotopic map to bypass the hair cells and stimulate the nerves directly.
Hearing aids just amplify sound so you still need intact hair cells. Cochlear implants bypass the hair cells
How does spatial localization occur at low frequency?
Low- phase shifting
High-shadowing from head and pinna
How is frequency encoded at low frequency?
At high frequency?
1. Volley theory/phase locking
2. Tonotopic map (cochlea to cortex)
What is high tone deafness?
Exposure to extremely loud sounds degenerates the organ of corti at the base or the cochlea
What are three ways to encode sound intensity?
1. Recruit more neurons with different thresholds
2. Increased the probability of firing for recruited neurons
3. Loss of spatial resolution at loud stimuli (soft sound at 2000Hz only will recruit the 2000Hz tonotopic neurons, but loud 2000hz sounds will recruit 1500, 2000 and 2500Hz tonotopic neurons)
What are the two different ways sound can be conveyed into the ear (2type of conduction)?
What is damage to each type of conduction called?
1. Air conduction- sound wave goes to tympanic membrane through middle ear to cochlea. Damage to this pathway is conduction deafness.
2. Bone conduction- sound travels through vibrating tuning forks through the bones and the skull to the 8th nerve. Damage to this pathway is sensorineural deafness.
What is Rinne's test?
What would the results be for normal, conduction deaf, sensorineural deaf?
Compare the patients hearing with a tuning fork by bone and air conduction.
Place tuning fork on the mastoid process and when the sound can no longer be heard, remove it but hold it in front of the ear.
Normal- air conduction is better than bone
Conduction deafness- bone is better than air in involved ear
Sensorineural deafness- air is better than bone in involved ear but both forms of conduction are diminished
What is Webers test?
What would be the results for normal, conduction deaf, sensorineural deaf?
Place the tuning fork on the forehead to test both ears at the same time. Ask if they can hear the sound in both ears or if it is louder in one.
Normal- heard equally in both ears
Conduction deaf- sound is louder in abnormal ear (because when your air conduction decreases, your bone conduction will increase to amplify)
Sensorineural deaf- sound is louder in the normal ear
What is the path of processing and relay of auditory info?
Where does the signal become bilateral?
2. Superior olive (bilateral)
3. Lateral leminiscus
4. Inferior colliculus
5. Medial geniculate of the thalamus
6. Auditory cortex
A lesion in the nervous system post-cochlea leads to what deficit?
Overall hearing depression because it is all in the same tract.
What is the processing role of the medial superior olive?
Sound localization by computing interaural time differences.
It integrated input from the left and right ant. Ventral cochlear nucleus to determine phase shifts.
Only works at low frequency because it requires phase locking
What processing occurs in the lateral superior olive and medial nucleus of the trapezoid body?
What structures are involved?
What stimulates the cells? Inhibits them?
Sound localization by integrating left and right anterior ventral cochlear nuclei intensity differences.
Works best at high frequencies because the wavelengths are shorter and it utilizes shadowing from head and pinna.
These cells are stimulated by ipsilateral input and inhibited by contralateral input.
Where do nuclei of the lateral leminiscus receive input from?
What is their function?
Contralateral cochlear nuclei
They process the onset and duration of sound
What is the function of the inferior colliculus?
1.Generating an auditory space map for localization
2. Process "important sounds" like speech
What are the functional properties of the medial geniculate complex (MGC,MGN, MGB)
1. Receives input from the inferior colliculus
2. Relays to cortical areas
3. does frequency comparison
4. Temporal comparison by location on ms time scale (echo) not phase-locking
How is the primary auditory complex organized?
Into columns that receive "EE" stimulus (excited by both ears)
"EI" stimulus (excited by one inhibited by one)
Where is the secondary auditory cortex located?
What does it process?
Inferior on the temporal lobe and it processes complex sounds
Where are the speech recognition centers located?
Which hemisphere usually processes speech?
Posterior to the primary cortex for lateralization of function for speech processing.
The left or dominant hemisphere generally processes speech
What is the developmental window for speech?
What does that mean?
If a language is learned prior to the teen years (14) the person can perceive and develop the language without an accent.
What does the non-dominant hemisphere process in terms of speech?
Inflection and emotional tone (prosody)