Task 7: Ear Flashcards
Physical definition of sound
Sound is pressure changes in the air or other medium. Referred to as ‘sound stimulus’.
Perceptual definition of sound
Sound is the experience we have when we hear. Referred to as ‘sound perception’.
Sound wave
Pattern of alternating high- and low-pressure regions in the air, as neighboring air molecules affect each other.
Condensation
Region of increased pressure on a sound wave that pSounushes surrounding air molecules together, resulting in air pressure above atmospheric pressure (= increased density).
Rarefraction
Region of decreased pressure on sound wave that spreads out air molecules to fill in increased space, resulting in decreased density.
Vibration with sine-wave motion is described by x2
- Frequency
2. Amplitude
Frequency
Number of cycles per second that pressure changes repeat (hertz, Hz)
- perceptual quality of pitch
- higher frequency = higher pitch
Amplitude
size of pressure changes determined by difference in pressure between high and low peaks os sound wave (decibel, dB)
- perceptual quality of sound
- higher amplitude = louder
What are the building blocks of sounds?
pure tones
Harmonic
made up of a number of pure tone components
Fundamental
first harmonic, a pure tone with frequency equal to fundamental frequency
Fundamental frequency
lowest frequency component of a complex periodic sound, that provides it with the strongest audible reference
Higher harmonics
Pure tones with frequencies that are whole-number multiples of fundamental frequency
What 2 things do you add to create the waveform of a complex tone?
- fundamental frequency
2. harmonics
What does a frequency spectra?
is another way to represent harmonic components of complex tone
Threshold
Smallest amount of sound energy that can just barely be detected
Loudness
Perceived intensity of a sound that ranges from ‘just audible’ to ‘very loud’
Magnitude estimation (Stevens)
Procedure that determines relationship between level in decibels (= physical) and loudness (= perceptual)
Thresholds and loudness depend on… x2
- decibels
2. frequency
Audibility curve
Indicates threshold for hearing versus frequency
- The upper curve is the threshold for feeling.
Auditory response area
Green area above the curve in which tones can be heard.
What is the range of frequencies for conversational speech?
2000 to 4000 Hz
What tones result in pain?
tones above threshold of feeling
Equal loudness curve
Indicate sound levels that create same perception of loudness at different frequencies.
Pitch
Psychological aspect of sound related mainly to fundamental frequency.
Low fundamental frequency leads to ___ pitches and vice versa
low
Why is pitch only labelled “high” or “low”
it is a psychological property of sound
Tone height
Perceptual experience of increasing pitch that accompanies increases in tone’s fundamental frequency.
Tone chroma
Notes with the same tone are considered to have same tone chroma.
Effect of missing fundamental
Effect in which the pitch remains the same, even if fundamental or other harmonics are removed.
Periodicity pitch
Perceived in tones that have harmonics removed. Indicates that pitch is determined by period or repetition rate of sound waveform
What does the auditory canal protect?
middle ear structures from outside world and enhances the intensities of some sounds by resonance
Resonance
Occurs when sound waves reflected back from closed end of auditory canal interact with sound waves entering the canal.
Tympanic membrane vibrations it sent to ….
o
Function of ossicles?
to translate sound energy from air medium (outer ear) to fluid membrane (inner ear)
What are the ossicles composed of?
3 small bones (malleus, incus, stapes)
How do the ossicles work?
the malleus (attached to membrane) vibrates, trasmitting this to the incus which transmits this to the stapes
How does the stapes transmit sound energy into the inner ear?
pushes on membrane covering window sending vibrations into inner ear
Middle ear muscles
- Attached to ossicles.
- At very high sound levels, they contract to dampen ossicles’ vibration:
-> It reduces transmission of low-frequency sounds;
-> Helps prevent intense low-frequency components from interfering with
perception of high frequencies.
What makes the makes transmission of sound vibration from air of middle ear difficult?
liquid inside ear
Cochlea
Main structure in inner ear, filled with liquid, containing the organ of Corti.
What causes the liquid of the cochlea to vibrate?
Movement of staples against oval window sets liquid inside cochlea into vibration.
Scala vestibuli vs scale tympani
Scala vestibuli: upper half of uncoiled cochlea.
Scala tympani: lower half of uncoiled cochlea.
Cochlear partition
Structure separating the scala vestibuli and tympani. It extends from base of cochlea, to its apex at far end.
As basilar membrane moves…
it exerts shearing force on cilia against tectorial membrane.
Organ of corti
It sits on basilar membrane and contains hair cells, the receptors for hearing. These are extended the entire length of the cochlea. Arching over these cells, is the tectorial membrane.
Cilia
Thin processes extending from top of the hair cells, which bend in response to pressure changes.
Name and explain 2 types of hair cells
- Inner hair cells: one row of these.
- Outer hair cells: three rows of these. Tallest row of cilia on outer hair cells is in contact with tectorial membrane, which plays a crucial role in activating hair cells, along with the basilar membrane.
_____ are translated into traveling waves in the basilar membrane
Vibrations of liquid inside cochlea
Up-and-down motion of basilar membrane has 2 results
- It sets organ of Corgi into an up-and-down vibration (blue arrow in image above) and;
- It causes tectorial membrane to move back and forth (red arrow in image above).
What causes the hair cells of the cochlea to move?
tectorial membrane slides back and forth above inner hair cells
What leads to changes in firing rate of auditory nerve cells?
- Movement to right
- Movement to left
Shearing of hair cells
- Movement to right (increase in pressure) – Causes tip links to stretch, activates the cell and attached auditory nerve fibers fire. Result = release of neurotransmitters, which diffuse across the synapse separating inner hair cells from auditory nerve fibers and causing them to fire.
- Movement to left (decrease in pressure) – Causes tip links slacken, stopping the firing.
Phase locking
-high frequency tones
Auditory nerve fibers fire in synchrony with rising and falling pressure of pure tone
- High frequency tones: may not cause nerve fiber to fire every time pressures changes (= refractory period).
-> One fiber might miss change in pressure, but since there are many, some of them fire.
= Combination of response of many fires shows that overall firing matches f
frequency of sound stimulus.
Place code
Different frequencies are signaled by activity in neurons that are located at different places in auditory system
Tonotopic map
Place vibrating the most depends on frequency (hair cells are activated at different frequencies and places along cochlea).
Neural frequency tuning curve
Maps different frequencies along cochlea to measure sound level needed to cause neuron to increase firing
Characterisitc frequency
Frequency to which a particular auditory nerve fiber is most sensitive. It is also the lowest point on the curve.
Temporal code
Tuning of different parts of cochlea to different frequencies, in which information about a particular frequency of an incoming sound wave is coded by the timing of neural firing as it relates to period of the sound.
Volley principle
Idea that multiple neurons can provide temporal code for frequency if each neuron fires at distinct point in period of a sound wave but does not fire on every period.
- Timing of firing matches frequency of sound stimulus, thus providing information about the fundamental frequency, as the repetition rate stays the same when latter is removed
Primary central auditory pathway
Cochlear nucleus -> Superior olivary nucleus -> Inferior colliculus -> MGN -> Auditory cortex
Cohlear nucleus
First brain stem nucleus at which afferent auditory nerve fibers synapse.
Superior olivary nucleus
Brain stem region where inputs from both ears converge.
Inferior colliculus
Midbrain nucleus in auditory pathway.
Medial geniculate nucleus (MGN)
– Part of thalamus that relays auditory signals to temporal cortex and receives input from auditory cortex.
In which lobe is the auditory cortex?
temporal
Hearing loss typically involves the _____ of sound thresholds.
elevation
Conductive hearing loss
- otitis media
Conductive hearing loss: hearing loss caused when middle-ear bones lose ability to freely convey vibrations from tympanic membrane to oval window.
-> Otitis media: inflammation of middle ear, in which it fills with mucus and
causes conductive hearing loss.
Presbycusis
Hearing loss greatest at high frequencies, caused by hair cell damage resulting from cumulative effects over time of noise exposure, ingestion of drugs that damage hair cells, and age-related degeneration.
Noise-induced hearing loss
Occurs when loud noises cause degeneration of hair cells. Damage of organ of Corti is often observed in these cases.
Sensorineural hearing loss
Type of hearing loss or deafness, in which the root cause lies in inner ear or sensory organ (= cochlea).
Hidden hearing loss
Does not normally affect person’s ability to hear sounds, but it makes it harder to hear sounds when there is background noise
Cochlear implant device
electronic hearing aid, that amplify sounds for people with hearing impairments
Cochlear implant
a microelectrode that stimulates directly the auditory nerve, has benefited many individuals with profound deafness.
Discuss the 5 steps of a cochlear implant
- External microphone collects sound waves and;
- Speech processor converts sound waves into electrical impulses;
- These are then transmitted to receiver implanted under skin;
- Receiver sends electrical impulses to microelectrode array implanted within cochlea.
- Electrodes stimulate correct populations of auditory fibers so that electrical signals are propagated to appropriate regions of cochlear nucleus and then to higher auditory processing centers.
Auditory brainstem implant
a prosthesis consisting of a microelectrode that directly stimulates one of auditory processing centers of brainstem and might restore hearing to patients with no auditory nerve or lesions beyond cochlea.
Audiogram test
Gold standard of hearing tests, in which patients listen to sounds of different frequencies at different volumes, in order to determine their thresholds for sound detection.
-> People with damaged hair cells have trouble detecting low-volume sounds at certain frequencies.
