l7

Question 1

phase locking low vs high frequency

Answer 1

low- neurons phase lock and fire at each phase of cycle
- gives additional information about timing
high- cannot keep up to phase lock instead use tonotopy

Question 2

how are APs conveyed on a ms time scale

Answer 2

action potential takes longer

• how can we compete faster if input to brain is slower
• because whole population gives informaiton not just 1 neuron

Question 3

3 cues for sound localization

Answer 3

distance (forward and backward)
elevation (veritcal) most difficult to locate
azimuth *horizontal)

Question 4

cue 1- direct/reflection ratio

Answer 4

direct- if someone is close by
reflection- if someone is far away sound reflects off surfaces
compare frequencies of direct/reflect to tell how far they are
(must be in enclosed room)

Question 5

cue 2- loudness

Answer 5

distand sounds hav elower loudness than close ones

Question 6

cue 3- sound spectrum

Answer 6

high frequencies are more quickly dampened by the air than low
- distant sound source sounds more muffled

Question 7

cue 4- movement

Answer 7

when listener is moving, sound sources pass by faster than distanct sound sources

Question 8

cues for horizontal localization

Answer 8

monoaural cues - 1 ear
bilateral cues-
interaural time difference
interaural level difference

Question 9

vertical cues

Answer 9

pinna viltering

Question 10

interaural time difference measuring

Answer 10

for sound source infront: ITD = 0
can accurately localize 1 degree
directly to the side: around 600us diff (size of head)
can accurately localize 15 degrees

Question 11

formula for ITD

Answer 11

time = distance/speed

= .20m/343m/s = 0.00000058 or 600us

Question 12

jeffress model

Answer 12

coincident input is required for activation: binaural inputs converge

• axonal path length differences cause specific delay
• when neural delay is offset by ITD of the same magnitude the coincidence occurs and cell fires
• only at a ceratin ITD

Question 13

AVCN axons

Answer 13

nucleus laminers in auditory systtem of owls shows shows evidence for delay lines in neurons on one side and not in the other

Question 14

medial superior olive

Answer 14

where comparison is thought to happen in mammalian brain- bushy cells synapse from hair cells and sendoinput to MSO

• also have contralateral delay lines from cochlea on oppsoite side
• excited by ipsilateral and contra AVCN
• inhibited by MNTV and LNTB

Question 15

expermental ITD

Answer 15

placed animal in sound proof room and recorded from auditory brain stem
- change time difference in sound to stimulate positions

Question 16

neural response vs interaural time difference graph

Answer 16

when ear leads by too much there is no response, as it gets closer you see response

• positive ITD then you see firing
• neurons sensitive to small window time (200us)

Question 17

interaural phase difference

Answer 17

ONLY LOW FREQUENCEIS- needs to phase lock

transient: difference in time of arrival of first wavelength at two ears
sustained: on going time differences

Question 18

periodic ITDs in MYSO

Answer 18

vary delays- doesnt like 500ms but like 1100, doesnt like 1500 this is because delay corresponds to certain phase phases and it repeats over and over, get a cyclical characteristic response

Question 19

varying frequencies at MSO

Answer 19

perodicity oc cycles now varies because each frequency will come in and out of phase at diff times
low freq- longer
high freq- shorter
have same best delay no matter what frequency (if not optimal freq you get lower repsonses)

Question 20

MSO frequency tuning

Answer 20

lower frequencies mostly

• tonotopically organized emphasizing low frequencies
• dorso-ventral tonotopic gradient
• high freqs ventral

Question 21

head shadow- localization cue

Answer 21

high frequencies take advantage of second factor - interaural intensity difference due to head shadow

Question 22

ILD of LSO & MNTB

Answer 22

excited by ipsilateral ear (globular bushy cells)
inhibited by contralateral ear (globular bc)
binaural suppression

Question 23

calyx of held

Answer 23

largest synapse in brain

Question 24

lateral superior olive

Answer 24

majority of cells receive excitatory input from VCN, inhibitory input from contra VCN via ipsi MNTB
e and i inputs have identical spectral receptive fields

Question 25

what is respone determined by

Answer 25

balance between excitation and inhibition

response = excitation - inhibition

Question 26

MSO vs LSO frequencies

Answer 26

MSO- low

LSO- high

Question 27

mso outputs

Answer 27

DNLL and ICC (dorsal low frequency)

Question 28

LSO outputs

Answer 28

bilaterally:
- excitatory projections to DNLL and ventral ICC on contralateral
inhibitory projections to DNLL and ICC on ipsilateral