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Temporal processing 2

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.

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Temporal processing 2

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  1. Temporal processing 2 Mechanisms responsible for developmental changes in temporal processing

  2. 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.

  3. Neural representation of temporal characteristics of sound

  4. 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.

  5. Development of phase-locking in human infants

  6. Evoked potentials as measures of phase locking and synchronous transmission

  7. ABR waveform development

  8. Cortical potential waveform development

  9. Evoked potential latency development as a measure of temporal processing

  10. ABR latency development

  11. ABR latency development

  12. ABR latency development

  13. ABR latency development

  14. Cortical potential latency development

  15. Possible anatomical correlates • Myelination • Other aspects of neural transmission • Axonal, dendritic maturation • Synaptic development

  16. Timing of different aspects of neural structural development

  17. 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.

  18. 6 mo 1 mo Dendritic development

  19. Organization of auditory cortex

  20. Axonal development in auditory cortex

  21. Myelination and synaptic transmission contribute to development of ABR latency

  22. Model of ABR generation

  23. Myelination and synaptic transmission contribute to development of ABR latency

  24. 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.

  25. Complications imposed by adaptation

  26. Susceptibility to adaptation in immature neurons

  27. Evoked potential measures of adaptation • Rate effects • Forward masking

  28. Rate effects in human infants: Wave I

  29. Rate effects in human infants: Wave V

  30. Comparison of ABR waves on rate effect

  31. ABR interpeak interval rate effect

  32. Forward masking with ABR

  33. ABR susceptibility to forward masking

  34. 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.

  35. 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.

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