Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
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. • 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.
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
Absolute sensitivity Development of conductive efficiency
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.
Transfer function of the external ear 4k 8k 16k
Absolute sensitivity Cochlear sensitivity?
Absolute sensitivity Neural transmission
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?
What else do we need to know? • Cochlear sensitivity • Growth of neural response with age • Older ages • More central parts of the nervous system
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.