temporal processing 2 mechanisms responsible for developmental changes in temporal processing

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

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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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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

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1 month 3 mo 6-12 mo 1-3 yr 4-6 yr adults0

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Forward masking with ABR

ABR susceptibility to forward masking

Adults Newborns0

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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.