BMS248 Lecture 8 - Sound localisation and sensory interaction Flashcards
What is sound localisation?
The ability to tell the direction from which a sound is originating
Why is sound localisation important?
- Survival
- Provides a perception of auditory space - differences in loudness/timing between the two ears
What are the two methods to localise sounds in the horizontal plane?
- Interaural level differences (ILDs)
- Interaural timing differences (ITDs)
What are Interaural level differences - ILDs?
- Difference in the loudness level of the same sound at the two ears
- Size of ILD depends on distance from centreline - Zero ILD would be a sound on the centreline (both ears hear it equally)
- High frequency sounds
What are Interaural timing differences - ITDs?
- Difference in the arrival time of the same sound at the two ears
- Size of ITD depends on distance from centreline - Zero ITD would be a sound on the centreline (both ears receive sound at the same time)
- Low frequency sounds
- excitatory - excitatory
Where are the level and timing differences detected?
The brain stem
What is the order of circuitry of sound localisation?
- Ear
- Cochlear nucleus (CN)
- Lateral Superior Olive (LSO) - ILD
- Medial Superior Olive (MSO) - ITD
- Medial Nucleus of the Trapezoid Body (MNTB)
- there is one of each centre on both sides of the midline (each centre has a near and far ear)
How does the ILD circuit function? - The LSO Excitatory-Inhibitory Pathway
- Each LSO receives an excitatory input from near ear and an inhibitory input from far ear
- The MNTB makes the input from far ear inhibitory - indirect
- The outputs if two LSOs are opposite but balanced - this gives an indication of sound position
E.g. if sound from left side of head:
- Output of left LSO high
- Output of right LSO low
How does the ITD circuit function? - The MSO Excitatory-Excitatory Pathway
- Each MSO receives 2 excitatory inputs - one from each ear
- MSO becomes maximally active when both inputs arrive simultaneously
- Neurons are from near and far ear are different lengths - key to function
- Output of left MSO is maximum for sound close to right ear and vice versa
- Combined balanced and opposite output gives an accurate indication of sound position
What are the major differences between the circuitry of ILDs and ITDs?
- ILD: excitatory-inhibitory
ITD: excitatory-excitatory - ILD: left LSO tuned to left side of head
ITD: left MSO tuned to right side of head
A shifted visual map in owls has what effect on the auditory map
Imposes the same shift
- The auditory space map is modified based on changes to the visual space map
The visual map is dominant for what kind of perception?
Space perception - used to realign the auditory map if there is differences between the two
How quickly do the visual and auditory maps adapt to changes in the field?
- Visual: rapidly adapts
- Auditory: takes longer to adjust
How does adaptive plasticity occur in the owl midbrain?
Auditory map in the ICX is aligned with the visual map in the OT with instructive feedback
What is the Central Nucleus of the Inferior Colliculus (ICC) tuned to and what adaptivity to the prisms
Central Nucleus of the Inferior Colliculus (ICC)
- Contains neurons tuned to specific ITDs
- The ITDs are in sound frequency-specific layers
- These neurons show little adaptive tuning to prisms
