L10 - Sound Localisation and Sensory System Interction Flashcards
What 3 things are sound localisation important for?
Important mechanism for survival
Important for communication
Enables perception of auditory space
What is the importance of sound localisation as a mechanism for survival?
For prey and predator
Owl and bat - nocturnal hunting
What is the importance of sound localisation for communication?
Identify where and who people are
Concentrate on one person in a noisy environment – cocktail party effect
How does sound localisation enable perception of auditory space?
All information is taken from features of sound arriving at the two ears
Map is formed that is not intrinsically represented on receptor cells like it is in visual system
What are the two benefits of sound localisation?
Know exactly where a sound is
Improve speech understanding
How does sound localisation help you identify where a sound is?
Know what direction it is moving
Predict where it will move next
Feel part of the 3D world even with your eyes closed
How does sound localisation help improve speech understanding?
Know where people are – you can turn and listen or run away
Help to hear individuals in a noisy environment
What are monaural cues for sound localisation?
Requires input from one ear
Sound elevation in the vertical plane - elevation
Characteristic notches that differ depending on the elevation of the sound
Head related transfer functions
What are binaural cues for sound localisation?
Requires input from both ears Sound position in the horizontal plane - azimuth Either - Interaural timing differences - ITDs - Interaural level differences - ILDs
Interaural timing differences - ITDs
Difference in the arrival time of sound at the two ears (Δt)
As small as 10μs
Mainly low frequency sounds
Interaural level differences - ILDs
Difference in the intensity of sound at the two ears (ΔI)
As small as 1-2dB
Mainly high frequency sounds
Do people use single or both binaural strategies?
Most species use both binaural strategies
- One can dominate based on animals hearing range and head size
- Also depends on evolutionary history
Where are sound localisation centres found?
Found in the Superior Olivary Complex in the Brainstem
Hair cells –> aVCN –> LSO –> MSO –> MNTB
What is involved in interaural level differences?
LSO – MNTB binaural excitatory-inhibitory pathway
Lateral superior olive (LSO) and medial nucleus of the trapezoid body (MNTB) involved
Interaural level differences method
Encoded by cells in the LSO that compare the coincidence of excitatory ipsilateral and inhibitory contralateral inputs
The two LSOs act as broad hemispheric channels tuned to sounds in each hemisphere
Overall position of a sound is encoded by the balance in average output rate of LSO channels
Interaural level differences evolution
Evolved over 200 million years ago – mainly high frequency (4-18KHz)
Very conserved among all mammals
Interaural level differences - sound coming from left method
- Input from left ear goes to the aVCN
- Excitatory input to cells in the LSO
- Input from right ear goes via MNTB and changes to inhibitory input
- Cells in the LSO detect balance between excitatory and inhibitory inputs
Interaural timing differences pathway birds
MSO binaural excitatory-excitatory pathway
Interaural timing differences method birds
Encoded by cells that compare the timing in arrival of excitatory ipsilateral and contralateral inputs
The cells are tuned to a particular timing difference for sounds originating from contralateral side
- Created by neuronal delay lines
Overall position of a sound is encoded by the particular channel activated
Interaural timing differences evolution birds
Mainly low frequency hearing (100Hz–3KHz)
Very conserved among birds
Interaural timing differences - how it works birds
As sound moves round the head the time it takes to get to the MSO is lower so it progressively activates cells as we go down to the shortest time difference
In the centre cells from both side MSOs are activated
The closer the sound is to the ear, the longer the pathway needs to be for activity to be coincidence in the cell
Interaural timing differences method mammals
Encoded by cells in MSO that compare the coincidence of excitatory ipsilateral and contralateral input
The two MSOs act as broad hemispheric channels tuned to sounds from the opposite hemisphere
Overall position of a sound is encoded by the balance between the average population response of the two MSO channels
Interaural timing differences evolution mammals
Mainly for low frequency hearing (<3KHz)
Evolved later in mammals and is not very conserved
Sound localisation in mammals summary
ILDs are represented in the LSO
ITDs are represented in the MSO
Both ITDs and ILDs are represented by two hemispherically tuned channels
Sound localisation in birds summary
ITDs are encoded by individual cells that are tuned to a narrow range of ITDs
This produced a hardwired topographic map of ITDs
That of mammals is more dynamic and adaptable
How was visual dominance of space perception during development shown?
Demonstrated by Knudsen and Knudsen on juvenile barn owls
Showed the plasticity of auditory orienting behaviour
Owls looked 20o to the right when wearing the prism glasses
How do prisms affect information flow in the midbrain auditory localisation pathway? - before prisms
ITDs are mapped to frequency specific layers in the ICC
These frequency layers converge to forma space map in the inferior colliculus
Auditory map in the inferior colliculus is aligned with the visual map in the optic tectum with instruction from the optic tectum
How do prisms affect information flow in the midbrain auditory localisation pathway? - after prisms
Instruction from the optic tectum realigns the inferior colliculus to match
Shows dominance of visual input over the auditory receptor field
What is sensory interaction?
Combination of different sensory modalities from a common source
Our ability to perceive objects requires?
Multisensory integration
What does sensory interaction improve?
Precision Discrimination Speed of perception Improving reaction Selective attention Motor output
What is the McGurk effect an example of?
Visual and auditory interaction
What is the McGurk effect?
Our perception is context dependent – use the most statistically reliable cue to inform decisions
- Visual cues for spatial decisions
- Auditory cues for timing decisions
- Either can dominate
Sensory interaction is highly reliant on temporal synchrony or small delays that allow prediction
What is the cocktail party effect an example of?
Selective attention
What is the cocktail party effect?
Our ability to selectively attend to a single object is an important survival mechanism
- Improves task performance and motor output
Works by resetting rhythmic brain oscillations and is important for associating multisensory information during selective attention
What are the 4 key processes of the cocktail party effect?
Active exploration of the scene active sensing
Selective attention to speaker
Stimulus driven entertainment
Cross modal predictive cues are involved in phase resetting
What is active exploration of the scene active sensing?
Involves motor and visual systems to scan the scene
Fixations enable the phase resetting (PR) of brain oscillations
What is selective attention to speaker?
Phase resetting synchronises the oscillatory activity in the appropriate sensory areas to the temporal pattern of the speech stream
What is stimulus driven entertainment?
Visual cues and the auditory waveform fine tune the entrainment to the speech stream in the auditory cortex
Cross modal phase resetting occurs
How are cross modal predictive cues involved in phase resetting?
Facial articulation and head movement precede speech
Auditory system can anticipate what is coming
Enhanced tracking of auditory stream from visual predictions
What is the most statistically reliable input for topographic information?
Visual
What is the most statistically reliable input for temporal cues?
Auditory
Why does perception require multisensory integration?
Relies on predictive alignment of oscillatory brain waves in different sensory areas
Alignment of sensory streams allows?
Allows us to perceive individual sensory objects and devote our attention selectively to one when we are confronted with may
2.5% of the population are?
Supertaskers
What are supertaskers?
Brain activity in supertaskers is lower than normal
Show enhanced neural efficiency that leads to better performance with a decrease in brain activity and volume
The reduced burden on these brain areas gives an improved ability to focus on more than one demanding task at a time
What is ventriloquism?
Our strong visual association with mouth movement and speech is known as ventriloquism
