Quiz 2 Flashcards
frequency coding
- what happens during a “peak”?
- high vs low freq
- threshold tuning curve
- outer hair cells
peak = when stereocilia bent the most = AP fired
- peak occurs near oval window for high freq
- near helicotrema for low freq
- absolute threshold for indiv auditory nerve fibers as a function of frequency –> lowest threshold is at characteristic freq
- outer hair cells improve sensitivity and frequency selectivity (sharpness of tuning curve –> respond to a narrower range of freq)
two-tone suppression
- frequency code
decrease in firing rate of auditory nerve fibre to its characteristic frequency when a 2nd tone of similar freq is presented at the same time
- frequency code for complex sounds is not the sum of individual AN fiber responses to indiv pure tones (complicates sensory coding)
isointensity curves
- curve represents what
- curve = APs vs freq –> plot multiple intensities
- there is a loss of frequency tuning in auditory nerve fibers at higher intensities (higher dB) –> curve flattens instead of having a sharp peak –> all neurons across the basilar membrane are responding
rate saturation
point at which an AN fiber is firing as rapidly as possible and further stimulation cant increase the firing rate
- AN nerve fibers fire faster for higher freq
phase locking
- definition
- above what freq do you need to use volley
- what is the volley principle –> what freq
AN fibres fire at distinct point (phase) in cycle of sound wave –> provides a temporal code for sound wave freq
- at frequencies above 1000Hz AN fibers cant fire on every cycle
- volley principle: hypothesis that combining firing of a group of fibers matches freq of incoming sound (1000-4000Hz) to provide a temporal code for freq
(basically they take turns firing to get the right freq code)
sound frequency coding
- 500-4000Hz
- below 500Hz
- above 4000Hz
500-4000Hz: both temporal (firing rate) and place (place of maximal firing) coding
below 500Hz: timing of firing in AN nerve (temporal = firing rate)
- can’t use place coding because the basilar membrane envelope is too broad for good freq discrimination –> no sharp envelope of activation
above 4000Hz: place of maximal firing on basilar membrane
high vs low spontaneous fibers
- low
- high
- sound intensity coding (+ example)
low spontaneous fibers: high threshold, maximum rate above 60dB –> don’t fire when no sound is present, does not respond to low intensities –> only responds to high intensity sounds so it tells brain about changes in high intensities –> has thinner axons (spontaneous firing rate is related to axon diameter)
high spontaneous fibers: low threshold, maximum rate below 60dB –> codes intensity changes at low intensities –> saturates at high levels of sound –> cannot distinguish between high dB
sound intensity is coded by the number of fibers of each type firing
eg. the characteristic freq is 1200Hz, but a weak 1200Hz tone has a similar firing pattern to a strong 1400Hz tone since they are similar freq –> brain is able to tell the difference between a weak 1200Hz tone and a strong 1400Hz tone through high and low intensity fibers
intensity coding vs frequency coding
- how the graphs look different
Intensity: more AN fibers fire as sound intensity increases (curve gets bigger)
Frequency: AN fibers from diff regions of basilar membrane fire when intensity is constant but the frequency is changed (whole curve moves over)
ipsilateral vs contralateral
monaural vs binaural
ipsilateral: same side of body
contralateral: opposite sides of body
monaural: input from one ear
biaural: input from both ears
central auditory pathway
- SONIC MG (+2)
path goes from:
- cochlear nucleus: first synapse in auditory pathway
- SON: superior olive nucleus
- IC: inferior colliculus
- MG: medial geniculate nucleus
- auditory cortex (A1)
cochlear nuclei
- cochlea connection
- dorsal, posteroventral and anteroventral
- monaural to biaural
cochlea to ipsilateral cochlear nucleus (3 subdivisions)
- dorsal cochlear nucleus: no synapse in SON
- posteroventral cochlear nucleus: synapse in CONTRALATERAL SON
- anteroventral cochlear nucleus: synapse in CONTRALATERAL OR IPSILATERAL SON
*note: until superior olive, everything is monaural –> crosses happen at SON –> becomes biaural –> need both ears to localize sound
inferior colliculus
- SON
- dorsal cochlear nucleus
- medial geniculate nucleus
- left and right
- SON to ipsilateral inferior colliculus
- dorsal cochlear nucleus to the contralateral AND ipsilateral inferior colliculus (bypasses SON)
- inferior colliculus to ipsilateral MGN
- connections between left and right inferior col.
medial geniculate nucleus
- inferior col
- A1
- inferior col to ipsilateral MG
- MG to ipsilateral auditory core region (includes A1)
olivocochlear bundle
- function (+speed?)
- efferent fibers location + function
- Ach release
- suppress continuous background noise to make sounds easier to detect –> protects against damage from loud sounds (not fast tho, must go from ear to SON and back to ear)
- efferent fibers are in the olivocochlear bundle –> control electromotility of outer hair cells –> innervate outer hair cells (come from SON) –> synapse with cochlea –> elongate and contract
- Ach released by efferent –> decrease in [K+] = hyperpol = elongation
auditory cortex
- location
- auditory core region (3)
- auditory association cortex (2)
- tonotopic map
- located in sylvian fissure (lateral nucleus)
- auditory core region: includes A1, rostral core and rostrotemporal core
auditory association cortex:
- Belt: inside sylvian fissure –> surrounds ACR
- parabelt: can see from outside of brain; partially surrounds belt
- tonotopic map: neurons that respond to diff freq are organized anatomically in order of freq (low CF = red, high CF = blue)
“where” pathway
“what” pathway
where: (aka dorsal) posterior parabelt to posterior parietal cortex to dorsolateral prefrontal cortex –> location
what: (aka ventral) anterior parabelt to orbitofrontal cortex –> pitch
audibility curve
- most sensitive + why
- standard threshold
- base boost
absolute threshold for hearing as a function of frequency = sound pressure level that you can JUST detect
- most sensitive from 2000-6000Hz –> pinna + auditory canal can amplify this range
- @1000Hz –> STD amplitude threshold is around 0 dB (but we can hear below 0dB)
- base boost: compensates for higher thresholds at high and low frequencies (without base boost, low pitch sounds will stop being heard first as loudness decreases)
hearing thresholds
- audiometer
- marking
- staircase procedure
- absolute threshold
- high vs low freq
audiometer: instrument used to measure absolute threshold (dB) for pure tones of diff freq
1: yes
0: no
- staircase procedure: decrease by 10dB until they cant hear, inc by 5dB until they can hear –> find dB level where they can hear 4 times (the absolute threshold is between the lowest dB they can hear and the next level below it)
- at lower freq it is more noisy = need more trials to get overall dB level
air vs bone conductance
- voice
air: cochlea stimulated (eg. headphones)
bone: vibration of skull
- your own voice is both air and bone conducted –> can hear low freq better –> ur voice in a recording is just air conduction
loudness perception
- confusion
- diff SPLs; duration
- matching task
- phon
subjective impression of sound intensity (often confused with intensity or sound pressure level)
- diff sound pressure levels can result in the same perceptual experience –> increases with duration of sound
matching: adjust intensity of comparison tone to match loudness of standard tone with fixed intensity and freq
eg. 1000Hz 40dB –> adjust dB of 2000Hz tone to it
phon: unit of loudness for pure tones obtained from matching experiments
- sound that is 20 phon sounds the same as a 20 dB 1000Hz tone
equal loudness contour
- examples
equal loudness contour: (for a single person) shows the sound pressure level necessary for comparison tones between 20 and 10,000Hz to achieve a match to the loudness of a 1000Hz standard tone of a fixed sound pressure level
(2 diff freq can sound the same if they’re on the same loudness contour, even if dB is diff; or 2 diff freq can sound diff if they’re on diff loudness contours even if they do have the same dB –> diff perception of SPL
scaling
- axes
- unit of loudness
- JND + webers law
if it was linear axes we would see a curve that levels off –> we use a power function with an exponent less than 1 (log log axes produces a line with a constant slope)
- loudness increases more slowly than intensity
sone: unit of loudness from a scaling experiment –> participants assign number to how loud diff SPLs seem to be (magnitude estimation) –> freq constant
- able to tell one sound is louder than the other (JND) requires 1-2dB change –> not a violation of webers law because dB scale is logarithmic! (increased intensity is still associated with an increase in sound pressure by louder amount to notice change)
pitch discrimination
- detection (range)
- what causes the JND to increase in an experiment?
- low freq?
detection: freq range of human hearing is 20Hz-20kHz (decreases with age)
JND increases as std freq increases
- we have good pitch discrimination at low freq (why place theory not fully correct)
masking
- measure
- bandwidth
- task
- result
- critical bandwidth example + explanation
- general finding
measure absolute threshold for detecting pure tone in the presence of nice (sound contains a wide range of freq)
bandwidth: range of freq of masking noise
task: do you hear the tone in the first interval or the second?
result: harder to detect the tone as the noise bandwidth widens, but only up to a point (critical bandwidth = bandwidth beyond which adding more freq to the masking noise does not raise the absolute threshold anymore)
- critical bandwidth will be a DIFFERENCE
eg. CB = 400 Hz –> 1800 to 2200 Hz
- increasing the noise higher than 1800 will increase the absolute threshold (bad thing) until you pass 2200 then it won’t make a difference (max interference)
general finding: lower Hz test tones have smaller critical bandwidths
- CB = 1mm on basilar memb –> low freq (helic.) are more spread out than high freq (oval window) on basilar memb –> 1mm near helic contains a smaller range of freq than the 1mm near oval window –> therefore there is a smaller CB for lower freq because they are less spread out
pitch perception
- AN fiber selectivity
- critical bandwidth
- example
AN fibers have a characteristic freq and respond to a narrow range of freq –> critical bandwidth interpreted as revealing the freq tuning of sets of auditory neurons used to detect the test tone (selectivity)
- freq outside the CB may stimulate a diff set of freq tuned neurons
eg. if 800Hz is the CF, and CB is 400Hz, AN fiber will respond to 600-1000Hz tones, but 800Hz best (lowest absolute threshold at 800Hz)
psychophysical tuning curves
- task
- result
- effect on pitch perception
- upward spread
- when can both tones be heard?
task: can you hear the test tone during the masking tone
result: greatest masking effect when masking tone and test tone have same freq (need more intense masking tone when not same freq) –> sharper curve
- suggests pitch perception depends on place code
- upward spread of masking: masking effects when not same freq are asymmetrical –> masking freq lower than test tone are more effective
- must have 2 separate peaks on basilar membrane for both tones to be heard
hearing loss types
- conductive loss
- sensorinerual loss (cochlear and auditory nerve)
- presbycusis
- conductive: disturbance in mechanical transmission of sound through outer or middle ear
- usually uniform loss at all freq, caused by injured ear drum, infections, or abnormal growth of ossicles - sensorineural: cochlear or AN damage
a) cochlear damage: decreased activity or injury of hair cells; usually restricted to certain freq, caused by infections, genetic diseases, ototoxic drugs, aging, exposure to sudden or prolonged loud sound
b) retrocochlear dysfunction: damage to AN; often unilateral; often caused by tumors
2.1. presbycusis: usually sensorineural, usually bilateral, loss begins at high freq, but includes lower freq with advancing age; wearing out of hair cells (near oval window first = high freq)/degeneration of stria vascularis (lines middle canal, keeps endolymth healthy + ions balanced)
hearing loss assessment
- healthy ears
- conductive loss
- sensorineural loss
- acoustic reflex threshold
healthy ears: cochlea stimulated by air or bone conducted sounds
conductive loss: can hear bone, not air
sensorineural: cannot hear bone and air –> doesn’t matter how sound is getting to inner ear since inner ear is the part that is the problem
acoustic reflex threshold: softest sound that elicits reflex is normally 70-100dB (pretty loud)
- having an elevated or absent reflex may occur with middle or inner ear damage/retrocochlear dysfunction
ipsilateral vs contralateral reflexes
- ipsilateral
- contralateral
- middle/inner ear problem
- retrocochlear dysfunction
ipslateral reflex: right ear stimulation causes right reflex, left ear stimulation causes left reflex
contralateral reflex: right ear stimulation causes left reflex, left ear stimulation causes right reflex –> happens when signal crosses to opposite SON (facial nerve stimulates middle ear)
status of ipsilateral vs contralateral reflexes can indicate site of damage
eg. middle or inner ear problem: if ipsilateral reflexes are affected, so are contralateral (for damaged side)
- right inner ear damage causes abnormal right and left reflexes with right ear stimulation, but normal right/left reflexes with left ear stimulation
eg. retrocochlear dysfunction: different ipsilateral and contralateral reflex patterns
- right SON damage causes abnormal right and normal left reflex, with either right or left stimulation
Hearing loss treatment
- hearing aid (2 design components)
- behind the ear
- in the ear
- bone anchored
- surgery
- cochlear implants
- brainstem implant
- future
hearing aid: for conductive or sensorineural loss –> amplifies sound pressure –> best with selective amplification for frequencies with greatest loss –> should keep high intensities at comfortable level
- additional method is to move energy from frequency regions in which hearing is poor (usually high frequencies) into regions where hearing is normal (lower freq)
- behind the ear: useful if some inner ear function remains
- in the ear: good for mild to moderate hearing loss
- bone anchored: surgically implated behind damaged ear –> used for conductive loss or severe unilateral sensorineural loss
- surgery: conductive loss –> replace ossicles if immobilized; graft tympanic membrane
- cochlear implants: severe sensorineural loss –> transforms sound into electrical signal –> electrode array stimulates AN fibers at appropriate positions along cochlea
- brainstem implant: retrocochlear dysfunction –> electrical stimulation of auditory brainstem nuclei
future: sensorineural loss –> regeneration of hair cells (not yet in humans)
hidden hearing loss
- cause
- hypothesis
exposure to high levels of noise can decrease your ability to use sound even when ability to detect sound remains normal (according to audiogram) –> caused by loss of synapses between AN fibers and hair cells (loss of connectivity
- hypothesized that this is why some ppl have difficulties listening in noisy situations (affects ability to understand speech or enjoy music)
sound localization
- azimuth
- elevation
- eg. left side path
- ILD
- largest vs no intensity difference
- high vs low Hz waves
- ITD
azimuth: left/right direction of sound source (straight ahead = 0 degree azimuth)
elevation: up/down position of sound source
eg. if path of sound is on the left, it will reach right ear with lower intensity (some sound will bounce off head)
ILD: interaural level differences –> only present at frequencies above 1000Hz (curves below are flat)
- largest intensity differences occur when sound comes from directly left or right (90 degrees)
- no intensity diff for sounds directly in front or behind (0 or 180)
- high Hz sound waves bounce off head –> only some get to other ear
- low Hz sound waves pass by head with no reflection
ITD: interaural time difference: if not directly in front or behind, there will be a difference in the moment that the sound wave reaches the ear (90 degrees = largest difference)
superior olive
- MSO
- LSO
- interaural info available in the superior olive
- medial superior olive (MSO): neurons sensitive to ITD –> fire APs when stimulated by specific lag between L and R ear signals (small place differences on left and right basilar memb –> peaks happen at diff times)
- lateral superior olive (LSO): neurons sensitive to ILD –> excitatory connections from ipsilateral ear, inhibitory connections from contralateral ear (inhib sent by MNTB to LSO) = results in extra excitation in one ear, and inhibition in the other ear
cone of confusion
- time differences
- ILD
- prediction
- explanation (2)
interaural time differences for diff positions around the head –> every position in front of head has the same ITD as a position behind the head
- ILD also are ambiguous
- cone of confusion: predicts we should find it difficult to tell if sounds come from in front or behind us (but we don’t!)
- able to tell because when we move our head horizontally, it changes the intensity and time differences = disambiguate location of stimulus
- also able to tell because of the shape of our pinna –> unique –> different frequencies reflected from front and back (energy at eardrum not equally intense even tho it is equal at sound source)
directional transfer function
DTF: shape of pinna and upper body change intensity of sounds w diff freq that arrive at each ear from diff locations in space
- sound from each aimuth and elevation has its down DTF; DTF diff for each subject too (diff pinna)
vestibular sense
- what is it for
- semicircular canals (3)
- otolith organs (2)
- change in head motion (2)
- change in position of head with respect to gravity
- qualities of vestibular stimuli (2)
equilibrium
semicircular canals: anterior, posterior and horizontal
otolith organs: utricle (horizontal) and saccule (verticle)
change in head motion (acceleration)
- semicircular canals - angulatory (rotary) acceleration
- otolith organs - linear acceleration
change in position of head with respect to gravity
- otolith organs - tilt
qualities of vestibular stimuli: direction and amplitude
vestibular sense - directionality
- 3 planes
- 3 axes
median (sagittal) plane: splits left and right
frontal (coronal) plane: splits front and back
transverse (axial) plane: splits top and bottom
x: points out front
y: points out left
z: points out top
vestibular sense - rotation
- roll
- pitch
- yaw
- linear motion (3 axes)
- tilt directions (3)
- lying down?
roll: rotation around x axis (ear to shoulder)
pitch: rotation around y axis (forward)
yaw: rotation around the z axis (shake head no)
translation directions for linear motion:
- backward and forward = x axis
- sideways = y axis
- up and down = z axis
tilt directions: (tilt = single move and stay there)
- pitch = forward or backward
- roll = left or right
- no yaw tilt because there is no change in gravity for yaw
- note: if you’re lying down and moving ur head there is no tilt bc no change in gravity
rotary acceleration
- path of stimulation
- kinocilium
- head rotation
- towards vs away
- receptor potential
- stimulates receptors in the ampulla of each semicircular canal (ant, post, and horiz)
- stimulates hair cells in the crista of the ampulla –> stereocilia of hair cells are embedded in cupula (jelly sheet)
- longest stereocilia = kinocilium –> aligned so that all kinocilium point in same direction
- head rotation causes endolymph to move in opposite direction –> cupula deflected, stereocilia bend toward kinocilium, neural signal (K+ channels open, causes depol –> excitatory –> releases glu into synapse with vestibular nerve fibers)
- bending away from kinocilium = hyperpol (inhibitory –> channels close –> reduced glu = dec firing rate)
receptor potential: graded; slow change in membrane voltage that is proportional to stereocilia bending
direction coding - semicircular canals
- maximal sensitivity axis
- horizontal canal
pitch and roll
- right vs left anterior canal
- posterior canals
- push pull response (right side, left side, firing rate)
- amplitude coding
- each semicircular canal is maximally sensitive around the axis that is perpendicular to it –> not sensitive to the other 2 axes
- horizontal canal responds to vertical axis (z axis) –> therefore sensitive to yaw turns (horizontal canal forms a loop around z axis) –> very easy to study saw
pitch and roll: all 4 canals responsible
- left and right anterior canals sensitive to same axis (oblique) but in opposite directions
- same for posterior –> same axis but opposite directions
push-pull response: yaw motion to the right
- right side: causes endolymph to move to the left; stereocilia bend toward kinocilium, depolarizes hair cells
- left side: endolymph move left, stereocilia bend away from kinocilium, hyperpolarizes
- firing rate increased in right vestibular nerve (excitatory), decrease in left vestibular nerve (inhibitory)
amplitude coding: one direction = how much above spontaneous rate; other direction = how much below spon level
otolith organs
- instead of ampulla
- otolithic membrane
- kinocilia arrangement (utricle vs saccule)
- linear movement vs tilt
- utricle –> which axes, which movements
- saccule –> which axes, which movements
- direction coding
- amplitude coding
- constant velocity
- have macula instead of ampulla
- stereocilia embedded in otolithic membrane (jelly)
- kinocilia arranged towards striola in utricle and away from striola in saccule (striola divides each macula into 2 halves)
- moving your hear forward/backward (linear) causes otocina (CaCO3 –> covers stereocilia embedded in otolithic membrane) to lag behind in opposite direction, but tilting causes them to go in same direction bc of gravity –> both cause stereocilia to bend = causes depol
utricle: horizontal –> sensitive to x and y axes linear acceleration; pitch and roll tilt
- cells on one side are sensitive to forward/backward,
saccule: vertical –> sensitive to x and z axes linear accel; pitch tilt
direction coding: tilt/linear accel in opposite directions cause opposite changes in firing rate
- tilt increases firing rate –> continues to respond whole time head is tilted –> on opposite side hair cells will be inhibited (push pull response)
amplitude coding: by firing rate –> higher for larger movements
- goes back to resting rate if it is at a constant velocity (reduction in response –> you stop feeling like youre turning)
vestibular system dynamics
- alcohol
- oculogyral illusion
- oculogravic illusion
- alcohol changes density of endolymph; cupula deflects as it does when head is spinning
- oculogyral illusion: visual disorientation and apparent movement following rapid body spins; cupula deflected in opposite direction before returning to resting state (why you feel dizzy after spinning –> otolith organs still doing stuff)
- oculogravic illusion: apparent backward tilt and visual elevation experienced during forward body acceleration; macula cant distinguish between displacements due to horizontal acceleration or to static head tilt (why you feel like youre being pushed in an airplane before you start moving)
judging distance
- 3 cues
cues:
- relative intensity: less intense with greater distance
- simplest, but requires some assumptions
- becomes useless when too far away –> inverse square law (intensity diff detectable only when close enough) - spectral composition: further away = more “muddier” sound
- high freq sounds decrease in energy more than low freq sounds because air dampens high freq more
- only noticeable at far distances - relative amounts of direct vs reverberant energy (close = mostly direct)
echolocation
some blind people can make clicks with their mouths and use the returning echos to sense obstacles
- for an fMRI scan, the brain regions associated with vision of an blind echolocation expert light up (but not in a non-expert)
