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Temporal processing 2. Mechanisms responsible for developmental changes in temporal processing. What needs explaining?. Immature performance in some temporal processing tasks as late as 11 years. More certainly, immature temporal processing in infants younger than 6 months old. - PowerPoint PPT Presentation
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Temporal processing 2
Mechanisms responsible for developmental changes in temporal
processing
What needs explaining? Immature performance in some temporal
processing tasks as late as 11 years. More certainly, immature temporal
processing in infants younger than 6 months old.
Neural representation of temporal characteristics of sound
Development of phase locking
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Phase locking takes longer to develop than frequency tuning.
Phase locking develops in the central nervous system later than at the periphery.
Development of phase-locking in human infants
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Evoked potentials as measures of phase locking and synchronous transmission
ABR waveform development
Cortical potential waveform development
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Evoked potential latency development as a measure of temporal processing
ABR latency development
B BB B B
B
33-34 35-36 37-38 39-40 41-42 43-441.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
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2.1
2.2
Conceptional age (wk)
ABR latency development
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ABR latency development
ABR latency development
Cortical potential latency development
Possible anatomical correlates Myelination Other aspects of neural transmission
Axonal, dendritic maturation Synaptic development
Timing of different aspects of neural structural development
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Development of myelination Appears in auditory nerve and brainstem
around 29 weeks gestational age Auditory nerve and brainstem
indistinguishable form adult by 1 year postnatal age
Begins prenatally in projection to thalamus, but colliculus-thalamus and thalamus-cortex take longer to reach adult stage.
Dendritic development
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1 mo
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6 mo
Organization of auditory cortex
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Axonal development in auditory cortex
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Myelination and synaptic transmission contribute to development of ABR latency
Model of ABR generation
Myelination and synaptic transmission contribute to development of ABR latency
Conclusions: development of phase locking Phase locking and neural synchrony
develop over a long time course. The auditory nerve and brainstem appear
to be mature in this regard earlier than other parts of the auditory nervous system.
Maturation of phase locking could be related to the development of some sorts of temporal processing.
Complications imposed by adaptation
Susceptibility to adaptation in immature neurons
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Evoked potential measures of adaptation Rate effects Forward masking
Rate effects in human infants: Wave I
Rate effects in human infants: Wave V
Comparison of ABR waves on rate effect
ABR interpeak interval rate effect
B
BB B B B
JJ
JJ J J
1 month 3 mo 6-12 mo 1-3 yr 4-6 yr adults0
0.2
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Age
B 50-10/sec
J 90-10/sec
Forward masking with ABR
ABR susceptibility to forward masking
Adults Newborns0
10
20
30
40
50
60
70 Forward masked
Slow rate unmasked
Conclusions: development of adaptation Before perhaps 3 months of age, infants
appear to be particularly susceptible to adaptation at the level of the brainstem.
This could explain infants’ susceptibility to forward masking at this age.
Conclusions: Mechanisms underlying development of temporal processing
Both phase locking and adaptation mature during infancy, at least at the level of the brainstem.
Low level neural immaturity may contribute to some immaturity in temporal processing.
Low level neural immaturity cannot explain infants’ poor gap detection performance, however.