intensity representation 2
DESCRIPTION
Intensity representation 2. Mechanisms underlying the development of intensity representation. What needs explaining?. Absolute sensitivity improves dramatically during infancy and then more slowly throughout childhood. - PowerPoint PPT PresentationTRANSCRIPT
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Intensity representation 2Mechanisms underlying the
development of intensity representation
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What needs explaining? Absolute sensitivity improves dramatically during
infancy and then more slowly throughout childhood.
Intensity discrimination and detection in noise are immature until 5 or 6 years of age.
Temporal tasks that involve intensity resolution mature over the same time period.
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What should we be looking for? Factors that influence absolute sensitivity
Conductive efficiency Cochlear sensitivity Neural transmission Physiological noise
Factors that influence intensity coding Growth of response with increasing intensity Variability in neural response
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Absolute sensitivityDevelopment of conductive
efficiency
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Development of external and middle ear
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Development of pinna
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Predictions about function of external and middle ear Increasing ear canal length and pinna size
will lead to a decrease in the resonant frequency of the external ear, as well as changes in spectral shape.
Changes in the middle ear cavity size, and possible structural changes in the middle ear will lead to changes in the efficiency of the middle ear.
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Transfer function of the external ear
4k 8k16k
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Middle ear impedance level
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Absorption level into middle ear
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Compare to threshold development
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Absolute sensitivityCochlear sensitivity?
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Click-evoked ABR threshold over age (preterm infants)
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Tone-burst evoked ABR thresholds (newborns)
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Tone-burst evoked ABR thresholds (infants)
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Absolute sensitivityNeural transmission
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Neural transmission continues to develop during infancy
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Three-month-olds’ absolute threshold is correlated with I-V interval
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Factors contributing to absolute threshold development Conductive efficiency--all the way to
adolescence, though effect is small after infancy
Probably not cochlear maturity-- at least after term birth
Neural transmission-- brainstem in early infancy; other parts of the brain later?
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Growth of cochlear microphonic with increasing intensity (rats)
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Growth of ABR Wave V amplitude with increasing intensity (infants)
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What else do we need to know? Cochlear sensitivity Growth of neural response with age
Older ages More central parts of the nervous system
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Conclusions Conductive development can account for a large part of
absolute threshold development during infancy and childhood.
Brainstem transmission accounts for additional immaturity of absolute threshold during later infancy.
Although there are hints that neural response grows with increasing intensity differently in infants, the existing data do not support any conclusions about sensory bases of immature intensity processing beyond early infancy.