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The Auditory System

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Katalin Tamasi

on 15 March 2011

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Transcript of The Auditory System

The Auditory System The physics and psychology of hearing The ear & the cochlea Central auditory processing How perception occurs Would you favor hearing to vision? Functions of sound speech music no social isolation What is sound? pressure changes in air, water etc. experience of hearing sound waves pure tones complex tones amplitude / loudness frequency / pitch Range of hearing Sound quality: timbre aid in localization sound perception:
1. sound stimulus receptors 11. pressure changes electrical signals III. signal pitch, loudness, timbre, location How does energy reach the receptors? Outer ear Middle ear Inner ear: the cochlea Cochlea & organ of Corti Sensitivity of the cilia Which & how fibers fire? Békésy's Place Theory of hearing Traveling wave motion Uncolied cochlea Envelope of the traveling wave The vibration of the basiliar membrane Tonotonic map of cochlea Frequency tuning curves Masking experiment Basiliar membrane vibrations Updating Békésy Basiliar membrane: frequency analyzer Fourier analysis made by the basiliar membrane Cochlea: frequency analyzer Phase locking I Phase locking II Auditory pathways How auditory processing occurs? What and where streams of hearing The auditory cortex Auditory cortex in the monkey Brain image of what and where streams Evidence from brain imaging How does perception occurs? Tonotopic map of the monkey Effect of traning in tonotopic maps Effect of the missing fundamental [demonstration] Additive synthesis Frequency spectrum Analogy to water waves Audibility curve Tympanic membrane & stapes Masking experiment I. Auditory brain stem response = test for hearing and brain function measures the electrical potential of the auditory nerve biological marker for learning disorders, dyslexia, autism slowing in nerve conduction: Rosenhall et al (2003): slow latencies between consecutive sequential waves in autistic individuals
i.e.: prolonged III-V interpeak latency Wave I, II: auditory nerve

Wave III: axons emerging from the CN

Wave IV, V: higher brain stem level Possible explanations: slower myelination of auditory nerves, lesions Method: Alternating 80 dB clicks were presented on a signal averager, within a frequency range of 150-2500 Hz

10% percent of the children required sedation Results Significant difference in the absolute latency of W I and V, interpeak latency III-V 1. large proportion of autistic children show ABR abnormalities
2. no simple ABR pattern can be shown in the autistic population Conclusions Masking experiment II.
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