L8-L10 Flashcards
What does an audibility curve depict?
absolute threshold for hearing as a function of frequency
Audibility threshold
the lowest sound pressure level that can be reliably detected across the frequency range of human hearing (20-20000 Hz)
Audiometer
an instrument used to measure the absolute threshold (dB) for pure tones of different frequencies
What 2 kinds of sounds stimulate the cochlea?
air-conducted sounds (e.g. headphones) and bone-conducted sounds (e.g. vibration of skull)
2 ways in which loudness perception is different from intensity
(1) different sound pressure levels can result in the same loudness perception depending on frequency; (2) loudness increases with duration of sound (up to 200ms) with intensity held constant
Temporal integration
the perception of loudness depends on the summation of energy over a brief, but noticeable, period of time (100-200ms)
3 methods used to study loudness perception
loudness matching, loudness scaling, and loudness discrimination experiments
Psychoacoustics
branch of psychophysics that studies the psychological correlates of the physical dimensions of sound
Task performed in loudness matching
adjust the intensity of comparison tones to match the loudness of a 1000 Hz standard tone of a certain intensity, resulting in an equal loudness contour
What does an equal-loudness contour depict?
the sound pressure level necessary for comparison tones between 20-20000 Hz to match the loudness of a 1000 Hz standard tone of a fixed sound pressure level (indicated by the number on each curve)
Phon
unit of loudness level for pure tones obtained from matching experiments; sound pressure level of an equally loud 1000Hz pure tone
Task performed in loudness scaling
adjust the intensity of a 1000Hz, 40dB tone to be twice as loud (2 sones), half as loud, etc.
Sone
unit of loudness from scaling experiments
What’s the JND for loudness?
a 1-2 dB increase in intensity is required to be able to notice any increase in loudness
loudness increases more slowly than intensity!
What is pitch perception related to in pure tones and complex tones?
frequency of pure tones and fundamental frequency of complex tones
Frequency range of human hearing
20-20000 Hz (can’t hear below or above regardless of intensity)
At what frequency range is pitch discrimination good?
low frequencies; JND increases as standard frequency increases
therefore, place theory of frequency coding can’t entirely explain pitch perception
Masking
measures the absolute threshold for detecting a pure tone in the presence of masking noise of varying bandwidth (range of frequencies with equal amplitude)
Why do psychoacousticians use masking experiments?
to investigate frequency selectivity
Critical bandwidth
bandwidth beyond which adding more frequencies to the masking noise does not raise the absolute threshold any further
General finding on critical bandwidths
lower frequency test tones have smaller critical bandwidths
What is the interpretation of critical bandwidths?
reveals the frequency tuning of sets of auditory neurons used to detect the test tone; frequencies outside the bandwidth may stimulate a different set of neurons
Upward spread of masking
masking effect is asymmetrical; masking frequencies lower than the test tone are more effective
Task performed in psychophysical tuning curves
adjust masking tone intensity until the low dB test tone (1 of 6 frequencies) that occur at some point during the masking tone is just detectable
When does the greatest masking effect occur?
hardest to hear the test tone when its frequency and that of the masking tone are equal
Ohm’s acoustical law
separation of sound components by auditory system based on Fourier analysis
Conductive hearing loss
disturbance in mechanical transmission of sound through outer or middle ear that usually results in uniform loss at all frequencies
3 causes of conductive hearing loss
injured ear drum, infections (otitis media), abnormal growth of ossicles (otosclerosis)
What kind of sound can be heard with conductive hearing loss?
bond-conducted sounds (via inner ear) but not air-conducted sounds
Otitis media
middle ear fills with mucus during ear infections
Sensorineural hearing loss
most common and serious form usually caused by cochlear or auditory nerve damage
What kind of sounds can be heard with sensorineural hearing loss?
cannot hear bone-conducted or air-conducted sounds
Cochlear damage in sensorineural hearing loss
characterized by decreased activity or injury of hair cells and is usually restricted to certain frequencies
Causes of cochlear damage in sensorineural hearing loss
infections, genetic disease, ototoxic drugs, aging, exposure to sudden or prolonged loud sound
Auditory nerve damage in sensorineural hearing loss
type of retrocochlear dysfunction (occurs beyond cochlea) that is often unilateral and caused by tumors
Presbycusis
age-related hearing loss that is usually sensorineural and bilateral; loss begins at high frequencies then low frequencies with advancing age
What damage in the ear causes presbycusis?
wearing out of hair cells with age and degeneration of stria vascularis (metabolic hearing loss)
Metabolic hearing loss
stria vascularis loses its ability to perform its job of bathing the cochlear partition with nutrients and ions, which reduces hair cell activity
What is used to assess hearing loss?
audiogram (normal threshold at 0 and elevated threshold indicating hearing loss)
Acoustic reflex
prolonged loud sounds cause the bilateral contraction of the tensor tympani and stapedius muscles regardless of which ear is stimulated
Acoustic reflex threshold
softest sound that elicits the acoustic reflex; normally 70-100 dB
Ipsilateral acoustic reflex
right ear stimulation causes right reflex; left ear stimulation causes left reflex
Contralateral acoustic reflex
right ear stimulation causes left reflex; left ear stimulation causes right reflex
What do the status of ipsilateral and contralateral acoustic reflexes indicate?
site of damage in the ear
Acoustic reflex affected by middle or inner ear problem
if ipsilateral reflex is affected in one ear, so are contralateral reflexes
Acoustic reflex affected by retrocochlear dysfunction
different ipsilateral and contralateral reflex patterns
Function of hearing aids
selective amplification for frequencies with greatest loss; compresses intensity differences to keep high intensities at comfortable level
3 kinds of hearing aids
behind-the-ear, in-the-ear, and bone-anchored hearing aids
When are behind-the-ear hearing aids used?
when some inner ear function remains
When are in-the-ear hearing aids used?
mild to moderate hearing loss
When are bone-anchored hearing aids used?
conductive loss or severe unilateral sensorineural loss; surgically implanted behind the damaged ear
Surgery for conductive hearing loss
replace ossicles if they are immobilized or graft a tympanic membrane
Cochlear implant
transmits sound into electrical signals, which activate electrode arrays that stimulate AN fibers at appropriate positions along the cochlea
When are cochlear implants used?
only for severe sensorineural loss
When are brainstem implants used?
retrocochlear dysfunction
Interaural time difference (ITD)
difference in time between arrivals of sound in one ear vs the other
Azimuth vs elevation in sound localization
left/right direction of sound source; up/down position of sound source
Which azimuths produce the largest and smallest ITDs?
when sound comes directly from the left or right (90°); when sound comes directly in front of (0°) or behind the head (180°)
Interaural level difference (ILD)
intensity difference between ears as a function of azimuth
Which azimuths produce the largest and smallest ILDs?
largest intensity difference when sound comes directly from left or right; no intensity difference for sounds directly in front or behind head (reaches ears simultaneously)
Why are ILDs only present at high frequencies?
high frequency sound waves bounce off the head, creating a sound shadow, and only some reaches the other ear; low frequency sound waves can pass by the head
ILDs only present at frequencies above 1000 Hz
Medial superior olive (MSO)
contain neurons that are sensitive to ITDs and fire APs when stimulated by specific lag between left and right ear signals
ITDs may create place differences on left and right basilar membranes
Lateral superior olive (LSO)
contain neurons that are sensitive to ILDs, which receive both excitatory and inhibitory inputs
Which ear do excitatory connections to LSO come from?
ipsilateral ear (originate in the left or right cochlea)
Which ear do inhibitory connections to LSO come from?
contralateral ear via the medial nucleus of the trapezoid body (MNTB)
Cone of confusion
region of positions in space where all sounds produce the same time and intensity differences (i.e. ITD and ILD are ambiguous)
2 ways to resolve ambiguous time and intensity differences in sound
horizontal rotational head movements; shape of the pinna (highly ear-specific input)
Directional transfer function (DTF)
graph showing the intensity of sounds over a range of frequencies that arrive at each ear from different locations in space (azimuth and elevation)
2 components of the vestibular sense
perception of spatial orientation and reflexive vestibular responses
3 sensory modalities of our perception of spatial orientation
angular motion, linear motion, and tilt (transduce different kinds of energy)
Examples of reflexive vestibular responses
eye rotation, balance, autonomic responses (motion sickness, blood pressure)
Graviception
ability to sense the relative orientation of gravity (i.e. tilt sensation)
2 types of vestibular sense organs
semicircular canals and otolith organs in the inner ear
Which vestibular receptors do changes in acceleration (rate of head motion) stimulate?
semicircular canals (angular acceleration) and otolith organs (linear acceleration)
Which vestibular receptors do changes in head position with respect to gravity stimulate?
otolith organs (e.g. head tilt)
2 qualities of vestibular stimuli
amplitude (velocity or magnitude of displacement of head movement) and direction
3 translation directions for linear motion
positive x-axis translation (forward and backward); positive y-axis translation (left and right); positive z-axis translation (up and down)
3 rotational directions
roll, pitch, yaw
Roll rotation
Clue: r
head stays in the frontal/coronal plane and rotates around the x-axis; “comme ci, comme ca” nods
Pitch rotation
head stays in the medial/sagittal plane and rotates around y-axis; “yes” nods
Yaw rotation
head stays in the transverse/axial plane and rotates around z-axis; “no” motion
2 tilt directions (with respect to gravity)
roll tilt and pitch tilt (no yaw tilt because movement is aligned with gravity)
Which receptors does rotary acceleration stimulate in the semicircular canal?
receptors in the ampulla of each semicircular canal (anterior, posterior, and horizontal)
Ampulla
swelling at the base of each semicircular canal that includes the cupula, crista, and hair cells, where transduction occurs
Receptor potential
slow change in membrane voltage that is proportional to stereocilia bending
Which semicircular canal is most sensitive to yaw turns?
horizontal canal (z-axis)
Push-pull response in semicircular canals
yaw motion to the right depolarizes hair cells in the right horizontal canal and hyperpolarizes hair cells in the left horizontal canal, which increases firing rate in the right vestibular nerve and decreases firing rate in the left vestibular nerve
What are the two otolith organs?
utricle and saccule, which both contain macula where sensory transduction occurs
How many hair cells in the utricular macula vs saccular macula?
30000 hair cells (horizontal); 16000 hair cells (vertical)
Push-pull response in otolithic organs
tilt or linear acceleration that maximally excites hair cells (and vestibular nerve fiber) on one side of the striola will maximally inhibit those on the opposite side
Oculogyral illusion
visual disorientation and apparent movement followed by rapid body spins; cupula deflected in opposite direction before returning to resting position
Oculogravic illusion
apparent backward tilt and visual elevation experienced during forward body acceleration; macula can’t distinguish between displacements due to horizontal acceleration or to static head tilt
