Neural Coding / Sound Localization Flashcards
Coding of Sound Features / Localization of Sound in Space
review: the sharpening mechanism provided by the ___________ (OHCs) to enhance the spatial resolution (frequency resolving power) of the basilar membrane
cochlear amplifier
the hearing range implies that each individual frequency is “best represented” by a patch of BM = to about ____ mm or about ____ um, which is at best _____ individual hair cells
0.02 mm; 20 um, 9-12 individual hair cells
manner in which info about a stimulus (sound or ant other sensory modality) is represented by neuronal activity
neural code
specific set of input patterns to which a neuron will respond
- think low level vs high level
- think broad vs narrow
(all diff types of sensory info)
receptive field
range of a stimulus parameter (intensity, freq, direction, etc.) which is reflected by neuronal activity
- neuronal activity. helpful for identification of stimulus parameter
dynamic range
auditory neurons response to stimulus intensity typically increase firing rate through the dynamic range of _____ dB but the response becomes saturated at that point
20-50 dB
what characterizes individual neuron?
neuron tuning curve
stimulate neurons @ lowest stimulus level
- least amount of energy need to stimulate
characteristic frequency
different characteristic frequencies have different what? (3)
1) different nerve fibers
2) different thresholds
3) different bandwidths
the characteristic frequency of a given fiber is roughly the same as the __________ of part of the BM that it is attached to
resonant frequency
minimal stimulus needed to produce a response at that charactersitc frequency is the ___________
threshold
_______ affects the neuron curve
ototoxicity
how can ototoxicity affect the neuron tuning curve?
(3 ways)
1) elevated threshold
2) widened bandwidth
3) shift of characteristic frequency toward lower frequency
characteristic frequency is directly related to the ___________ on BM
location
increased frequency means it is ________ to basal end of cochlear
closer
certain cells respond to certain types of stimulus
- freq dependent (auditory) or movement dependent (visual)
- most basic
- if this neuron is firing, this is what it means
labeled line code
express or relay info about the intensity of a stimulus
rate code
rate of firing of a given neuron is dependent on the _________
stimulus intensity
known as DR, auditory neuron rate increases through range of __________ and then __________
20-50 dB and saturates
aspect of stimulus = reflected by _________
firing rate, which carrys info
neuronal activity (firing) locked to the periodicity of the stimulus
temporal code
how can temporal code be useful?
useful for stimulus parameters that can be designated by that periodicity (frequency)
what are the limitations of the neural coding strategies?
they limit the firing limit of action potential mandates
different nerve fibers elicit different sensations by virtue of their central connections on BM
PLACE THEORY
acoustic info is carried by the rate or frequency of the discharge of a neuron
TEMPORAL THEORY
firing rate can be tuned to the frequency of certain stimuli
phase locking
______ theory can be seen in cochlear implants (benefits and limitations)
place
phase locked neurons fire to a ________ in sine wave cycle
specific point
phase locking works up for frequencies up to about _____ Hz
1000 Hz
group of neurons/hair cells that can work collectively to continue this place locking by sharing the responsibility of representing each part of the stimulus
volley principle
illustration of volley principle
which theory best accommodates the needs of the auditory system?
both place and temporal theory
widening of cochlear tuning with increasing intensity improves reproduction of the _________ pattern while degrading the spatial patterm
temporal
sharp tuning observed at LOWER frequencies facilitates _________
spatial resolution
- at the expense of temporal resolution
what is one of the most critical functions of the auditory system?
localization of sound in space
why is localization so important?
auditory signal recognizes - 13 ms as opposed to 1 ms
- time of arrival is different (shorter)
- system works with high accuracy & reproductivity (fidelity)
what two types of information does the central auditory pathways derive about localization
1) ITD (interaural time difference)
2) ILD (interaural level difference)
different between arrival times of acoustic stimulus at both ears
ITD
difference between stimulus amplitudes (intensities) at both ears
ILD
a change of 1-2 degrees in the location of a stimulus corresponds to an ITD of about ______ microseconds
13 microseconds
ITD works better with _____ frequencies
low frequencies
(one ear first then to second ear)
ILD works better with _______ frequencies
high frequencies
(head shadow effect - less intensity)
degree of exactness with which something is copied or reproduced
fidelity
______ is useful when sound waves are large enough to wrap around head and avoid shadowing
- wavelength of 500 Hz
- phase info (most useful below <1.5kHz
ITD
caused by shadowing of sound stimuli by structures of the head
- cues exist only for frequencies > 500 Hz and reliable for frequencies above 3kHz
ILD
________ differences between L and R ears are most effective for localization for higher frequency stimuli
ILD
_____ consists of stacks of neurons, each receiving inputs from both ears
MSO
where is MSO on the auditory pathway
SOC
MSO system detects which neuron receives _______ signals from both sides and determines localization based on that info
coincident (same time)
MSO works best for localizing ______ frequencies
lower
illustration for understanding MSO
which neurons get sent to both ears at same time
MSO and ITD illustration
________ consists of stacks of neurons, each receiving bilateral inputs, but the contra input has passed through the MNTB to become a inhibitory signal
LSO
LSO amplifies the level difference and allows even subtle ILD to be transformed into an ___________ response
an all-or-nothing
LSO is better with ______ frequencies
higher
ascending pathways: neuronal activity at any level, info can be extracted, may be modified by _________ feedback circuits
descending
what specializations are unique among sensory neural networks and allow for signal precision or fidelity (2)
1) ribbon synapses
2) giant terminals
- endbulbs
- calyces of Held
specialized transport & timing system for synaptic vesicle release designed for synapses that require a wide dynamic range and accurate sustained release
ribbon synapse
what can you think of the ribbon synapse as?
Ferris Wheel
- constantly tuning to provide accurate delivery of vesicles (NT) to BM
(time release & ongoing release)
where are ribbon synapses found?
in auditory system and portions of light system
ribbon is a very dense structure surround by ___________
synaptic vesicles
what do the endbulbs of Held consist of? (2)
staining neurons such as:
1) axosomatic terminals
2) spoon-shaped with filopodia
what is the LARGEST nerve terminal in CNS
Calyces of Held
the 2 terminals associated with Calyces of Held are associated with what pathways?
pathways used to localize in space
what do calyces of held arise from?
AVCN projecting to (synapsing on) the contra medial nucleus of trapezoid body (MNTB)
neither cue works well
- human localization in this range tends to be relatively poor as a result
around 2,000 Hz
____________ promote fidelity or accuracy of stimulus reproduction/analysis by the auditory system.
Synaptic specializations
