Quiz 2

Question 1

frequency coding

• what happens during a “peak”?
• high vs low freq
• threshold tuning curve
• outer hair cells

Answer 1

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)

Question 2

two-tone suppression

- frequency code

Answer 2

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)

Question 3

isointensity curves

- curve represents what

Answer 3

• 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

Question 4

rate saturation

Answer 4

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

Question 5

phase locking

• definition
• above what freq do you need to use volley
• what is the volley principle –> what freq

Answer 5

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)

Question 6

sound frequency coding

• 500-4000Hz
• below 500Hz
• above 4000Hz

Answer 6

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

Question 7

high vs low spontaneous fibers

• low
• high
• sound intensity coding (+ example)

Answer 7

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

Question 8

intensity coding vs frequency coding

- how the graphs look different

Answer 8

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)

Question 9

ipsilateral vs contralateral

monaural vs binaural

Answer 9

ipsilateral: same side of body
contralateral: opposite sides of body

monaural: input from one ear
biaural: input from both ears

Question 10

central auditory pathway

- SONIC MG (+2)

Answer 10

path goes from:

1. cochlear nucleus: first synapse in auditory pathway
2. SON: superior olive nucleus
3. IC: inferior colliculus
4. MG: medial geniculate nucleus
5. auditory cortex (A1)

Question 11

cochlear nuclei

• cochlea connection
• dorsal, posteroventral and anteroventral
• monaural to biaural

Answer 11

cochlea to ipsilateral cochlear nucleus (3 subdivisions)

1. dorsal cochlear nucleus: no synapse in SON
2. posteroventral cochlear nucleus: synapse in CONTRALATERAL SON
3. 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

Question 12

inferior colliculus

• SON
• dorsal cochlear nucleus
• medial geniculate nucleus
• left and right

Answer 12

• 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.

Question 13

medial geniculate nucleus

• inferior col
• A1

Answer 13

• inferior col to ipsilateral MG

- MG to ipsilateral auditory core region (includes A1)

Question 14

olivocochlear bundle

• function (+speed?)
• efferent fibers location + function
• Ach release

Answer 14

• 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

Question 15

auditory cortex

• location
• auditory core region (3)
• auditory association cortex (2)
• tonotopic map

Answer 15

• 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)

Question 16

“where” pathway

“what” pathway

Answer 16

where: (aka dorsal) posterior parabelt to posterior parietal cortex to dorsolateral prefrontal cortex –> location
what: (aka ventral) anterior parabelt to orbitofrontal cortex –> pitch

Question 17

audibility curve

• most sensitive + why
• standard threshold
• base boost

Answer 17

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)

Question 18

hearing thresholds

• audiometer
• marking
• staircase procedure
• absolute threshold
• high vs low freq

Answer 18

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

Question 19

air vs bone conductance

- voice

Answer 19

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

Question 20

loudness perception

• confusion
• diff SPLs; duration
• matching task
• phon

Answer 20

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

Question 21

equal loudness contour

- examples

Answer 21

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

Question 22

scaling

• axes
• unit of loudness
• JND + webers law

Answer 22

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)

Question 23

pitch discrimination

• detection (range)
• what causes the JND to increase in an experiment?
• low freq?

Answer 23

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)

Question 24

masking

• measure
• bandwidth
• task
• result
• critical bandwidth example + explanation
• general finding

Answer 24

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

Question 25

pitch perception - AN fiber selectivity - critical bandwidth - example

Answer 25

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)

Question 26

psychophysical tuning curves - task - result - effect on pitch perception - upward spread - when can both tones be heard?

Answer 26

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

Question 27

hearing loss types - conductive loss - sensorinerual loss (cochlear and auditory nerve) - presbycusis

Answer 27

1. 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 2. 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)

Question 28

hearing loss assessment - healthy ears - conductive loss - sensorineural loss - acoustic reflex threshold

Answer 28

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

Question 29

ipsilateral vs contralateral reflexes - ipsilateral - contralateral - middle/inner ear problem - retrocochlear dysfunction

Answer 29

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

Question 30

Hearing loss treatment - hearing aid (2 design components) - behind the ear - in the ear - bone anchored - surgery - cochlear implants - brainstem implant - future

Answer 30

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)

Question 31

hidden hearing loss - cause - hypothesis

Answer 31

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)

Question 32

sound localization - azimuth - elevation - eg. left side path - ILD - largest vs no intensity difference - high vs low Hz waves - ITD

Answer 32

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)

Question 33

superior olive - MSO - LSO

Answer 33

- 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

Question 34

cone of confusion - time differences - ILD - prediction - explanation (2)

Answer 34

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)

Question 35

directional transfer function

Answer 35

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)

Question 36

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)

Answer 36

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

Question 37

vestibular sense - directionality - 3 planes - 3 axes

Answer 37

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

Question 38

vestibular sense - rotation - roll - pitch - yaw - linear motion (3 axes) - tilt directions (3) - lying down?

Answer 38

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

Question 39

rotary acceleration - path of stimulation - kinocilium - head rotation - towards vs away - receptor potential

Answer 39

- 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

Question 40

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

Answer 40

- 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

Question 41

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

Answer 41

- 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)

Question 42

vestibular system dynamics - alcohol - oculogyral illusion - oculogravic illusion

Answer 42

- 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)

Question 43

judging distance | - 3 cues

Answer 43

cues: 1. 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) 2. 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 3. relative amounts of direct vs reverberant energy (close = mostly direct)

Question 44

echolocation

Answer 44

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)