Sensory System Interactions. Flashcards
What is sound localisation important for? And how does this mechanism help is a noisy environment?
important for communication. And localising where people are in specific locations.
We use this mechanism to focus on one thing in a noisy environment
The older you are the harder it is to do sound localisation
How does sound localisation allow for perception of auditory space?
Enables perception of auditory space
This happens from taking information from the environment by the both ears
Sound is used to create an auditory map (remember the eyes make a visual map)
What is binaural hearing?
Binaural hearing?
Is when you hear sounds with both ears.
This helps you to located where a sound is i.e if its up or down
This also helps you to PREDICT where a sound will move next.
What is monaural hearing?
This is when you only hear with one ear
You can hear all the sounds but you can’t bin point where its coming from
Sound localisation (detecting where in space a sound is)
How to recognise sounds in the vertical plane (this is the plane of detecting and localising sounds from ABOVE or BELOW )?
What are spectral notches?
What causes them?
We use monaural cues (which require only one input from one ear)
The brain can detect events such as spectral notches (specific points detected by sound vibration) which are precisely timed to the onset of sound hitting the ear.
These are caused by sound bouncing off of the pinna which is the fleshy part of the outer ear.
Different features of the outer ear responsible for helping vertical plane detection?
Every fold of the ear interacts with sound in a different way and distorts this sound
This distortion creates a specific pattern (which can be transferred by neurones)
NOTE Different sounds note are TRANSFORMED in different ways
This helps us to tell the elevation of sounds and where sounds are coming from in the ventral plane.
What can analysing the different patterns caused by sound distortion of the outer ear help us to do?
Helps us to recognise sounds from past experiences. Also helps us to tell where a sound is coming from in the vertical axis
How does the different shapes of the ears between individuals affect spectral notches
Causes spectral notches (certain points detected in the sound distortions which have to be learnt) to differ in person to person
What is the experiment which shows we have adaptive learning processes?
An ear has an insert placed into it
This modifies the direction of the transfer function (how sound is absorbed and processed)
This means the individual cannot recognise where the sound is coming from.
WHAT HAPPENS WHEN THE INSERT IS LEFT?
If the inserts are left in for a long time the individual can RELEARN transfer function and then go onto localising it (saying where the sound is coming from)
Thus this suggests we have adaptive learning. We can correct misaligned sensory input.
What helps us to detect and localise sound in the horizontal plane (as in left or right)?
We use two binaural cues:
Interaural level differences
And interaural timing differences
What are Interaural level differences?
The brain compares LOUDNESS and INTENSITY of sounds arriving at two different ears.
This means that is something is closer to one ear than the other then that sound is louder at the ear the sound is closest to.
The head physically defects sound so its quieter at the other ear.
Sounds as small as 1 -2 dN can be detected
The degree of detecting the difference in sound loudness corresponds on how far / close the sound is to the centre line of the body
This detects sounds at HIGH frequencies
What are interaural timing differences?
The brain compares the difference in the arrival of time of sound at both ears. This is as small as 10 micro sec
Sounds closer to one early than the other reach the ear quicker thats its closest to
This is compared to the sound hitting the other ear
This detects sounds at lower frequencies
Sounds furthest away from the midline (centre of head) gives the longest time differences
What do most species use, interaural timing or level differences?
They use both
However one may dominate due to animals head size and hearing range
Auditory pathway. Where do all nerves from the cochlear go? Where is the cochlear nucleus? What are the two pathways in the auditory system?
All the nerves from the cochlear enter the cochlear nucleus
This is in the brain steam
Then the pathway from the brainsteam has two places
Information is either sent to cells for recognition or it is sent from the ventral cochlear nucleus (in briansteam) to other regions of the brainsteam responsible for localising sound.
What is the auditory pathway? Starting with the superior olivary complex?
Starts with the superior olivary complex in the brainstem. This is the circuitry for localising sounds in space is. Remember the ventral cochlear nucleus is in this brainstem too.
From here the pathway goes up to the inferior and superior colliculus
It then travels up to the medial geniculate nucleus (MGN) remember the lateral geniculate nucleus is form vision.
And then the auditory cortex (AC)
What is the superior olivary complex?
This is found in the brainstemm
Here there is a collection of specialised neurones
These form distinct areas
These areas come about at the cell bodies and orientation of nerve fibres
What are the first auditory nuclei? And where do the neurones from the anterior ventral cochlear go?
Afferent nerve fibres from both ears which enter the cochlear nucleus
Neurones from the anterior ventral cochlear go to the superior olivary complex.
What three regions of the superior olivary cortex do neurones go to?
They go the the lateral superior olive
Then the medial superior olive
Then the medial nucleus of the trapezoid body
There are TWO of these. One each for each side of the head!
What cells in the lateral superior olive detect interaural level differences?
Small differences in intensity of sound are BETWEEN the two ears are detected by the principle cells
These cells in the LSO detect one EXCITATORY input from the anterior ventral cochlear nucleus on the same side as the head (the IPSILATERAL side of the head)
The contralateral (OTHER side of the head) side of the head sends inhibitory inputs to the LSO (Remember both sides of the head have an LSO, but the inhibitory input and the excitatory input in this instance both go to the same side of the head)
In the detection of interaural level differences, how does an inhibitory input go from one side of the head to the other? In this case to the opposite ear
So the inhibitory input from the opposite ear starts as an excitatory fibres from the anterior ventricle cochlear nucleus and it crosses the midline of the brain.
It then synpases onto the the MNTB on the opposite side of the head
This then sends the signal to the LSO
How is sound detected and localised from interaural level differences via the LSO?
The position of sound is encoded by the simultaneous arrival of excitatory and inhibitory inputs to the LSO neurones
Important to note about the LSO
There are two on each side of the head!!
Example of sound localisation when a speaker is on the LHS of the head, is at the centre of the head, and then on the RHS of the head:
This is in reference to what is happening at the left ear’s LSO. Note whatever is happening at the left ear the opposite is happening on the other side of the head.
When the speaker is on the LHS
The ispilateral going to the left LSO (on the same side) is positive and the contralateral input going to the left LSO is negative and small
When the speaker is in the centre of the head. The ipsilateral input going to the left LSO is LESS positive and the inhibitory input coming from the contralateral to the LSO is MORE neagtive. Ath this point the charges are equal to each other.
When the speaker moves to the RHS of the head. The positive input coming from the ipsilateral to the left LSO is much LESS positive and the contralateral input is much MORE positive.
Opposite happens for the other side.
When is there a overlap in both LSOs on both sides of the head?
When the sound is closer to the centre of the head. The positive and negative charges at the LSO become equal!
What do the two LSO’s act as? And how do they tell you the position of the sound in references to charges?
The two LSO’s act as broad hemisphere channels. This is tuned to sounds within the same hemisphere (remember this as it could be on the exam)
The overall position of a sound depends on the balance in the average output rate of these LSO channels. So basically the charges on the channels
The MORE positive a charge - the greater the output rate
How is sound localised in the horizontal plane using the interaural timing differences? I.e. what is the jeffress model?
This models relies on input from both ears alike the interaural level model but this relies on the combination of two excitatory inputs
MSO’s on either side of the head detect inputs at one ear and send this to activate another target neurone.
This Target neurone only becomes active when two excitatory inputs (one from each ear) hits it.
Interaural timing difference. What causes time delays? What is the time delay from a sound at the centre of the head and on either side of the head?
Sound from infront has the same time delay in being detected
Sound on either side of the head have varying delays
The MSO (found on either side of the head) detect the difference in time that excitatory inputs reach them.
When both are active they active a specific neurone downstream
The MSO is part of the delay line
What is common about delay lines in both humans and animals? What does the interaural timing difference model rely on? And what do both MSO’s act as ? How do we find position?
Delay lines are seen in both aminals and humans (the MSO)
The model relies on MSO’s and the detection of sound from both ears
The MSOs act as broad hemispheric channels and this is mainly tuned to sounds in the OPPOSITE hemispheres.
The BALANCE between average population response of both MSOs tells us location
So the key differences and similarities between monaural, binaural cues? And between ITDS and ILDS?
Sound in the vertical axis is detected by monaural cues
Sound in the horizontal detected by binaural
ITDS detect low frequency sound and are encoded by the coincidence of excitatory and inhibitory input in their LSOS
ILDS detect high frequency and are encoded in the coincidence of two excitatory inputs.
In mammals the ITDS and ILDS are tuned by two broadly tuned channels with the balance of output detecting sound
The sounds are tuned to the same hemispheres for ITDS but different hemispheres for IDLS
