Keating Flashcards
2 important aspects of sound localisation
absolute localisation
reletive localisation
define sound localisation
the ability to identify the direction of a sound source, whilst ignoring the other sounds in the acoustic space.
Importance: hearing a car without being able to see it before you step into the road.
ITD
biaural cue
Interaural time difference
Along horizontal plane or azimuth
Spectral cue
mount of energy at different frequencies (when a sound hits our pinna, the pinna will attenuate and boost certain frequencies which are dependent on where the sound is coming from spatially)
How does sound localisation adapt to a developmental hearing loss in one ear?
Remapping- being able to use the abnormal cues by remapping cue values into correct locations - this was mainly true of animals like barn animals and this was the mechanism for them to be able to compensate for 1 ear of hearing. - owl uses this
Reweighting- being able to ignore abnormal cues by increasing the relative weight given to cues that remain unchanged. Ignore the binaural cues and learn to rely on your good ear with spectral cues.-ferrets use this
Inferior colliclus role
relay for auditory infomation and sound localisation
Where does IC send afferents to
medial geniculate nuclues of thalamus
What is IC modualted by?
glutamatergic cells in L4&5, Helps to discrimnate multiple different sound sources.
what converges at IC
both ascending and desending pathways
where do inputs from both ears converge for the first time?
Superior olivary complex
Inferior colliculus properties:
- Organised frequency tonotopic map - With similarly tuned neurons responding to same frequencies beside one another (related to cardinal positions)
2.Dorsal lateral portion of the tonotopic map prefer low frequency - Ventral medial portions prefer high frequencies
4.Intermediate portions prefer intermediate frequencies
where is the only place in the brain you get a map of auditory space
superior colliculus
do you get an auditory map in the auditory cortex?
NO
* Neurons are broadly tuned to sound location and typically respond to contralateral space
Role of the AC in sound localisation
AC lesions =impaired localisation.
inactivating posterior AC
Less accurate sound localisation
Inactivating anterior AC
No effect
How is the sound processed in the AC?
Dorsal pathway -where is the sound, more of a sensorimotor pathway- sound for action
Ventral pathway- what is the sound
role of descending pathways?
learning and plasticity- adapt to altered sound localisation cues
effect on adapation with ear plug paradigm in descending pathway lesion
When these pathways are lesioned, then having hearing loss in one ear (putting ear plug on one side of the ferret model) means that while their ability to detect sound remains normal with both ears. But when they have hearing loss in one ear, they do not adapt as well as control animals to sound localisation
How does ferret adapt to developmental hearing loss in on ear
rear the ferrets from a young age to be ear plugged/ deaf for 80% of their life.
Adaptation-Learning now relies on monaural spatial cues but only
when wearing an earplug
what spectral frequency is importnat for adaptation to hearing loss in one ear
Juvenile-plugged
ferrets are more
sensitive to high
frequency features
Plugged behaviour is driven by features >16 kHz
reverse correlation
The process of reverse correlation implements the analysis of outputs to determine the inputs that the neuron will respond to with a spike.
to figure out which frequency
what did they learn abour cue reweighting
Cue reweighting is not observed when normal hearing is available
Juvenile-plugged ferrets adapt to an earplug by giving greater weight to the unchanged spatial cues provided to the intact ear
if plugged-relience on good ear, when unlugged effect reversed and they rely on both biaural cues again - context dependent plasticity.
would the ferret still be able to adapt if spectral cues were taken away?
yes- Juvenile-plugged ferrets possess a second adaptive mechanism that does not require spectral cues
Juvenile-plugged ferrets can learn to locate sounds correctly using abnormal binaural cues like the barn owl
Adaptive shifts in ILD tuning are seen bilaterally in primary auditory cortex (A1) of juvenile-plugged ferrets
Does auditory cortex have a map in the AC
NO- no explict map so use sound loclaisation as a model of nerual coding for spatial location,
describe representation of auditory space at the level of the cochlea
There is no representation of auditory space in the cochlea, sound localisation (at the level of the relay station inferior colliculus relays processing here) sound localisation serves as a good model for how auditory pathway deals with spatial hearing.
Who can adapt using remapping and reweighting
Both children in development and adults can adapt using altered binaural or spectral localization cues.
What do monaural deprivation stuides suggest aboutn certain periods - and how does this relate to jennifer?
As with other sensory functions, monaural deprivation experiments indicate that critical periods exist for the maturation of binaural hearing.
Under normal hearing conditions which cue is more reliable
binaural cues
which neural pathway and where is impacting plasiticty?
What neural networks or pathways in A1 are involved in plasticity: the cholinergic neuron in the basal forebrain that target the A1 also impair response when they are lesioned.
compare and contrast link to perceptual learning in visual cortex to auditory cortex
Brain areas involved for visual plasticity are higher visual areas like MT or V4.
In contrast to the visual system, auditory training results in more extensive plasticity at earlier stages of the cortical hierarchy, including A1.
Nevertheless, behavioral modulation of cortical responses has been found to be greater in higher-order auditory areas than in A1
How does visual infomation influence auditory spatial plasticity (link jennifer and bizley)
1.Having visual information can improve the accuracy of sound localization estimates
- Improves binaural cue discrimination (links to eye movements affecting auditory system)
What happens to auditory localisation if vision impaired?
auditory localization abilities can be altered if vision is impaired.
what happens to sound loclaisation if person is blind
Like the adaptation to a
unilateral hearing loss, more accurate sound localization
in blind humans is associated with greater dependence on
spectral localization cues. However, in blind subjects,
this superior use of spectral cues for localization in the
horizontal plane appears to come at the cost of a reduced
ability to use these cues for localization in the vertical
plane
Head movements (Carlise et al.,2014) & Coen link.
Encouraging human subjects fitted with pinna molds to make exploratory
head movements in order to maximize audio-motor feedback has been found to improve the rate and extent of
adaptation to altered spectral cues (Carlise et al.,2014) How active movements promote auditory spatial learning is unclear, but it is interesting to note that motor-related signals originating
in the secondary motor cortex can alter auditory cortical
activity- link to coen
