Sound localisation and sensory system interaction Flashcards
What are 3 reasons why sound localisation is important?
1) Survival
2) Communication
3) Perception of the auditory space
How is a perception in auditory space acheived?
- All information taken from sound arriving at both ears
- MAP of the environment is formed that is NOT intrinsically represented on receptor cells
What are 2 benefits of sound localisation?
1) Know where a sound is and where is is moving to
2) Can improved speech understanding
What are the 2 cues for sound localisation?
Where do they require input from?
1) Monaural cues (one ear)
2) Binaural cues (both ears)
What do monaural cues help to localise?
How is this different to binaural cues?
Monaural - sounds in the vertical place (elevation)
Binaural - sounds in the horizontal plane (azimuth)
What is the horizontal plane called?
Azimuth
What is the vertical plane called?
Elevation
What do the head and the shape of the ear do (in relation to sounds)?
What do these show?
Create hear-related transfer functions (HRTFs)
Characteristic notches in the recordings of an auditory nerve, depending on where is was received in elevation
What can HRTFs be used to create?
A map of how sound is amplified in the ear from different elevations and frequencies
What happens if you modify the outside of the ear with an insert?
The map changes and can no longer locate sound in the vertical plane
What are 2 examples of binaural cues to localise sounds?
1) Interaural TIME differences
2) Interaural LEVEL differences
What are 2 examples of binaural cues to localise sounds?
What strategies are normally used in a species?
What can cause one strategy to dominate?
1) Interaural TIME differences
2) Interaural LEVEL differences
BOTH strategies are normally used, but it depends upon evolutionary history
Hearing range
Head size - large head is better for timing, small head is better for levels
What are interaural TIME differences?
The difference in the ARIVAL TIME of sounds at the 2 ears
What are interaural TIME differences usually used for?
Why?
Low frequency sounds
High frequency sounds - time difference between the waves are much smaller and harder to detect
What are interaural LEVEL differences?
The difference between the INTENSITY of the sound at the 2 ears
What are interaural LEVEL differences used to detect?
High frequency sounds
What structure is involved in DETECTING timing/level differences of sound?
Where is it present?
Superior olivary complex
In the brainstem
What structure/s are involved in CALCULATING timing/level differences of sound?
Where are these present?
aVCN - anterior ventral cochlear nucleus
MSO - medial superior olive
LSO- lateral superior olive
MNtB - medial nucleus of the trapezoid body
Present in the superior olivary complex
In what pathway is interarual LEVEL differences calculated?
What area in the superior olivary complex is not involved?
LSO-MNtB binuaural excitatory inhibitory (EI) pathway
Doesn’t include the MSO
Describe the LSO-MNtB binuaural excitatory inhibitory (EI) pathway used to detect interaural level differences in sound (when sound is coming from the LEFT ear)
- Input from left ear to left aVCN
- Excitatory input from here to the left LSO
- Input from the right ear to the MNtB - excitatory input
- Inhibitory input from here to the left LSO
- LSO detects DIFFERENCES between excitatory and inhibitory inputs
- Excitatory input is larger than inhibitory input, loudness of sound in the left ear is very loud
- MAXIMUM output from the left LSO
What happens to the output from the left LSO when the sound moves from the left side of the head towards the right?
- Loudness heard in the left ear becomes less
- Inhibitory input from the right ear starts to become more than the excitatory input from the left ear
- LSO output becomes smaller until there is no output
How many LSOs are there in the brainstem?
2
When there is high sound at the left ear, which LSO has high output?
Low output?
High output - left LSO
Low output - right LSO
When there is high sound at the right ear, which LSO has high output?
Low output?
High output - right LSO
Low output - left LSO
In any auditory pathway, what is the first structure that the ‘sound’ travels to?
What does this structure then do?
aVCN
Anterior ventral cochlear nucleus
This structure sends EXCITATORY projections to structures further along the pathway
What are ILD encoded by?
What is the overall position of sound encoded by?
Cells in the LSO that compare the coicidence of excitatory and inhibitory inputs from the contralateral and ipsilateral ears
Overall position of sound is encoded by the BALANCE in the average output rate of these LSO channels
Is the ILD mechanism of hearing conserved?
Yes
In what pathway is interarual TIMING differences calculated?
What structures in the superior olivary complex are involved?
The binaural excitatory excitatory (EE) pathway
Strucutures involved:
- aVCN
- MSO
Describe the binaural excitatory excitatory (EE) pathway
- 2 excitatory inputs (one from the contralateral and one from the ipsilateral side)
- Coincidence of these inputs create activity in the MSO
Describe the binaural excitatory excitatory (EE) pathway used to detect TIMING differences in sound (when sound is coming into the right ear)
- In the left side of the head (ipsilateral) input from the left aVCN to the left MSO comes along a SHORT axon
- From the right side of the head (contralateral) input from the right aVCN to the left MSO is along a LONG axon
In the binaural excitatory excitatory (EE) pathway, what neuron is the input sent along if sound is going into that ear? Where to?
Why?
A LONG axon to the CONTRALATERAL side of the head
If the sound is at that ear, it is travelling faster than the other side of the head - needs to go along a longer pathway to meet the sound at the same time
When is there maximum output of the LEFT MSO?
When the sound is at the RIGHT ear
When is there maximum output of the RIGHT MSO?
When the sound is at the LEFT ear
What does the MSO respond to?
Sounds coming from the OPPOSITE side of the head
What is the overall position of sound encoded by?
The balance between the response of the two MSO channels
How many MSOs are there in the superior olivary complex?
2
What is the MSO called in birds?
The NUCLEUS LAMINARIS
What is the Jeffress model?
How is this different to in mammals?
Binaural excitatory excitatory (EE) pathway for BIRDS
Uses DELAY LINES - inputs from both sides of the head only meet each other in SOME cells in the NL
Describe the Jeffress model
- Input from the contralateral side of the head - inputs along a LONG neuron arrives at the NL in sequential progression
- Inputs from the ipsilateral side of the head reach the NL at the same time (along a short axon)
- Inputs from ipsilateral and contralateral sides of the head only meet each other in SOME cells in the NL
When is there activity in the MSO/NL?
When the input from the ipsilateral and contralateral sides of the head meet at the SAME time
In Jeffress model, what does the activated cell in the NL encode?
How?
A particular timing difference and a particular map in space
As specific cells in the NL are tuned to a particular timing difference of sounds from the contralateral side of the head, through delay lines
In Jeffress model, what happens in the NL as the sound travels around the head?
DIFFERENT cells in the NL are activated
What happens when sound is received in the centre of the head?
BOTH MSOs/LSOs are activated equally
What is the difference between the input from the NL in birds and the MSO in mammals?
Output from the MSO in mammals - decreases at travel around the head
Output from the NL in birds - activation of different cells as travel around the head
What important to localise sounds in the environment?
Sensory integration between the auditory system and the visual system
How was it demonstrated that the visual system was important in localising sounds in the environment?
Placed prisms on juvenile barns owls to modify their visual, so the owls thought they were looking 20 degrees to the left
1 day after prisms:
- Visual response shift 20 degrees
- Auditory response stays the same
42 days after prisms:
- Auditory response shift to match visual response
Prisms removed:
- Visual response back to normal but auditory response is still shifted
What do the added prisms affect?
What does this pathway consist of?
Information flow in the MIDBRAIN AUDITORY LOCALISATION pathway
Consists of:
- ICC (inferior colliculus central)
- ICX (inferior colliculus exterior)
- OT (optic tectum)
Describe the midbrain auditory pathway BEFORE prisms are added
- Interaural TIME differences are mapped to a frequency specific layer in the ICC
- These frequency layers CONVERGE to form an auditory space map in the ICX
- During development, the ICX is aligned with the visual map in the OT
- The ICX receives input from the OT
Describe the midbrain auditory pathway AFTER prisms are added
- The visual map in the OT is shifted
- Input from the OT to the ICX, realigning the ICX map to match the OT map
What is sensory interaction?
The combination of different sensory modalities created by a SINGLE SOURCE
What does sensory interaction improve?
- Precision
- Discrimination
- Speed of perception
- Reaction
- Selective attention
- Motor output
Describe the McGurk effect
- Eyes and ears compete for information
- Perception is context dependant - use the most statistically reliable cue to inform decisions
- Visual information or auditory information can dominate
What do we usually use visual cues for?
Auditory cues?
Visual cues for SPATIAL DECISIONS
Auditory cues for TIMING DECISIONS
What does sensory interaction depend upon?
Temporal synchrony
OR
Small delays that allow prediction of what the other input is going to be
What is the ‘Cocktail party effect’?
Selective attention
What does the cocktail party effect allow?
To focus on more than one thing at a time
Improvement of task performance and motor output
How does the cocktail party effect work?
By resetting rhythmic brain oscillations (PR - phase resetting) in order to synchronise the oscillations between different sensory modalities
What are the stages of the cocktail party effect?
1) Active sensing of the scene
2) Selective attention to speaker
3) Stimulus-driven entertainment
4) Cross-modal predictive cues
What does active sensing of the scene involve?
Motor and visual systems
When does the PR stage of the cocktail effect occur?
What happens during this stage?
When fixating on a certain speaker:
- PR synchronises the oscillatory activity in the appropriate sensory areas to the temporal pattern of the relevant speech stream
- Phases in the brain are reset to match the auditory signal from the person attending to
- Wave from PR influences other areas of the brain util finding a synchronous signal
What occurs in the stimulus-driven entertainment stage of the cocktail party effect?
Visual cues from mouth movement used to PREDICT auditory sound
Cross-modal PR occurs
What are ‘supertaskers’?
People who show enhanced neural efficiency, which leads to better performance with decreased brain activity and volume (brain is more efficient)
What can supertaskers do?
Multiple tasks at the same time
