Temporal processing 2

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Temporal processing 2

• Mechanisms responsible for developmental changes
  in temporal processing

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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.

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Neural representation of temporal characteristics
of sound
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Development of phase locking

• Phase locking takes longer to develop than
  frequency tuning.
• Phase locking develops in the central nervous
  system later than at the periphery.

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Development of phase-locking in human infants
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Evoked potentials as measures of phase locking
and synchronous transmission
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ABR waveform development
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Cortical potential waveform development
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Evoked potential latency development as a measure
of temporal processing
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ABR latency development
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ABR latency development
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ABR latency development
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ABR latency development
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Cortical potential latency development
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Possible anatomical correlates

• Myelination
• Other aspects of neural transmission
• Axonal, dendritic maturation
• Synaptic development

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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.

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Dendritic development
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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
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Model of ABR generation
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Myelination and synaptic transmission contribute
to development of ABR latency
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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.

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Complications imposed by adaptation
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Susceptibility to adaptation in immature neurons
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Evoked potential measures of adaptation

• Rate effects
• Forward masking

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Rate effects in human infants Wave I
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Rate effects in human infants Wave V
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Comparison of ABR waves on rate effect
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ABR interpeak interval rate effect
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Forward masking with ABR
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ABR susceptibility to forward masking
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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.

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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.