interaction between sensory systems

Question 1

how do we localise sounds

Answer 1

1) Interaural level differences (ILDs)
2) Interaural timing differences (ITDs)

Question 2

What are Interaural level differences (ILDs)

Answer 2

• The difference in the loudness (level) of the same sound at the two ears (ILD)
• The head acts as a barrier, reflecting or absorbing sound waves
• Size of ILD depends on how far sound is from the centreline

Question 3

What are Interaural timing differences (ILDs)

Answer 3

• The difference in the arrival time of the same sound at the two ears
• Sounds from one side reach the near ear first, and after a delay get to the far ear
• Size of ITD depends on how far sound is from the centreline

Question 4

are ILD or ITD more common for high freq sounds

Answer 4

Interaural level differences (ILDs)

Question 5

are ILD or ITD more common for low freq sounds

Answer 5

Interaural timing differences (ITDs)

Question 6

how do we localise sound

Answer 6

By detecting the ILD or ITD we know where the sound source is

Question 7

where are sound localisation centres

Answer 7

brainstem

Question 8

how does sound travel from ear -> brainstem

Answer 8

neurones from ear -> neurones in cochlear nucleus → lateral superior olive (LSO)/medial superior olive (MSO)/ and medial nucleus of trapezoid body (MNTB)

Question 9

how does sound travel from ear -> brainstem

Answer 9

neurones from ear -> neurones in cochlear nucleus → lateral superior olive (LSO)/medial superior olive (MSO)/ and medial nucleus of trapezoid body (MNTB)

Question 10

main centres involved in ILD and ITD

Answer 10

lateral superior olive
medial superior olive
medial nucleus of trapezoid body

Question 11

how are small differences in loudness detected

Answer 11

• detected in the LSO by the principal neurones
  1. The LSO neurones receive an excitatory input from near ear (+) and an indirect inhibitory input from far ear (–)
  2. excitatory input that crosses the midline to the MNTB on the same side as the LSO
  3. MNTB makes the input from the far ear inhibitory

Question 12

role of lateral superior olive (LSO)

Answer 12

involved in measuring difference in sound intensity between ears

Question 13

role of medial nucleus of trapezoid body (MNTB)

Answer 13

major source of inhibition in auditory brainstem circuitry

Question 14

how does the LSO detect volume differences between ears

Answer 14

• ear closest to sound = excitatory input to LSO > inhibitory input to MNTB
• output of LSO is determined by summation of opposing inputs

Question 15

how do the LSOs work together?

Answer 15

• each LSO receives positive input from near ear and negative input from far ear
• overlap of 2 LSO outputs = accuracy of localisation

Question 16

how do we detect interaural level differences

Answer 16

• the two LSOs act as channels tuned to sounds from each side of head
• each channel is made up of neurones tuned to different ILDs

Question 17

function of ITD/MSO EE pathway

Answer 17

→ detection of interaural timing differences

Question 18

how does the ITD/MSO EE pathway work

Answer 18

• small differences in sounds arrival time are detected in medial superior olive (MSO) by principle neurones
• 2 excitatory inputs (each ear) converge on MSO
• MSO becomes max active when BOTH inputs arrive at same time
• because neurones are different lengths, activity from far ear takes longer to reach MSO than near ear

Question 19

why do we get ITDs

Answer 19

ITDs result because the ears are physically separated in space by the head. Therefore, the direction-dependent differences in path lengths that sound must travel to reach each ear from the source will generate different times of arrival of the sound at the two ears

Question 20

how do MSOs work together

Answer 20

• for sound from left
  
  • L = MSO is low, R = MSO is high
• output of each MSO is highest for sounds from far ear
  
  • due to time delay required for coincidence

Question 21

how are ITDs encoded

Answer 21

ITDs are encoded by neurones in MSO that compare coincident arrival of excitatory inputs from both ears

Question 22

difference between ILD and ITD

Answer 22

left = LSO (sound from left), left MSO (sound from right)

Question 23

sounds in HZ plane are localised using which 2 methods

Answer 23

• interaural level differences (ILDs) = used for high freq sounds
• interaural timing differences (ITDs) = used for low frequency sounds

Question 24

where and how is ILD encoded

Answer 24

lateral superior olive
encoded by summation of excitatory and inhibitory inputs (EI)

Question 25

where and how is ITD encoded

Answer 25

• represented in MSO
• encoded by coincidence of 2 excitatory inputs (EE)

Question 26

are ILDs and ITDs adaptable or fixed based on genetic programmes?

Answer 26

both
- The initial connections are formed based on genetic programmes
- auditory map shows adaptive plasticity that depends on sensory function and sensory system interaction

Question 27

how did they conduct vision as sound localisation calibration in barn owls

Answer 27

• The owls visual field was artificially shifted and they looked at the effect this had on their ability to localise sounds
• assessed ability to localise stimuli using head movements
• They artificially shifted the owls visual field by 20o to the left using prisms in front of the eyes
  
  • To look at the target at 0o the head position will be 20o to the right of it
  • The owls hearing was not artificially modified at all

Question 28

The Measurement of Owl Head Orientation to Visual or Auditory Stimuli

Answer 28

1. owls were put into a dark recording chamber
2. head orientation was measured from the search coil on top of the owls head
3. The position of the light and sound stimulus were varied horizontally and vertically
4. A Shifted Visual Map Imposes the Same Shift on the Auditory Map