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P105 Lecture #20 visuals

P105 Lecture #20 visuals. 25 Feburary 2013. Acoustic Pressure is measured in decibels (dB ). 1 atm = 100,000 pascals = 10 11 micropascals Threshold: the softest sound detectable is 20 micropascals (at 1000 Hz). 2 parts in 10 billion of an atmosphere

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P105 Lecture #20 visuals

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  1. P105 Lecture #20 visuals 25 Feburary 2013

  2. Acoustic Pressure is measured in decibels (dB) • 1 atm = 100,000 pascals = 1011micropascals • Threshold: the softest sound detectable is 20 micropascals (at 1000 Hz). 2 parts in 10 billion of an atmosphere • We hear sounds 1-10 million times more intense than threshold • dB are logarithmic units with 0 dB at threshold • adding 20 dB = factor of 10 increase in pressure • 6 dB approximately doubles the pressure • 40 dB SPL = 20 x 100 = 2,000 micropascals Slide from Ian Shipsey, Purdue U., presentation on cochlear implants

  3. loud Hearing threshold of a profoundly deaf person (ex: Shipsey) Hearing threshold of a severely deaf person soft

  4. Slide from Ian Shipsey, Purdue U., presentation on cochlear implants The Ear Has Three Distinct Regions ca. 175 A.D. Galen Nerve transmits sound to the brain ca. 550 B.C. Pythagoras & successors It has taken until the present to unravel the rest

  5. Auditory System Physiology Illustration from E.J. Heller, “Why you hear what you hear”

  6. 3D Rendering of Auditory Transduction System • Show video “Auditory Transduction”, by Brandon Pletsch. (This video was awarded 1st prize in the 2003 NSF/AAAS Science & Engineering Visualization Challenge) http://www.youtube.com/watch?v=46aNGGNPm7s

  7. The tympanic membrane & ossicles 1543 Anatomist Andreas Vesalius describes the structure of the middle ear. Slide from Ian Shipsey, Purdue U., presentation on cochlear implants

  8. Why is our “sound sensor” not on the outside of our head? Impedance mismatch overcome by ratio of areas and lever action Hermann Ludwig von Helmholtz first to understand the role of the ossicles ( 1860’s) Slide from Ian Shipsey, Purdue U., presentation on cochlear implants

  9. Pressure Amplification in middle ear Lever action of ossicles (gives 1.5x amplification of force) Ratio of areas of oval window to tympanum (20x amplf’n of pressure Illustration from E.J. Heller, “Why you hear what you hear”

  10. Inner Ear Illustrations from E.J. Heller, “Why you hear what you hear”

  11. Slide from Ian Shipsey, Purdue U., presentation on cochlear implants The cochlea and its chambers 1561 GabrielloFallopio discovers the snail-shaped cochlea of the inner ear. The cochlea is about the size of a pea

  12. The Cochlea houses the Organ of Corti Auditory Nerve Slide from Ian Shipsey, Purdue U., presentation on cochlear implants

  13. Slide from Ian Shipsey, Purdue U., presentation on cochlear implants Organ of Corti 1st detailed study of Organ of Corti by Alfonso Corti Original figures (scanned) from: ZeitschriftfürwissenschaftlicheZoologie (1851) Hair Cells are mechano-electric transduction devices

  14. End of Early History The Middle Ages Georg von Békésy (Nobel 1961) Experimentally measured traveling wave profiles published by von Békésy in Experiment in Hearing, McGraw-Hill Inc., 1960. Hermann Ludwig von Helmholtz first theory of the role of BM as a spectrum analyzer providing a frequency-position map of sound Fourier components. Slide from Ian Shipsey, Purdue U., presentation on cochlear implants apex base

  15. Tonotopic Organization Slide from Ian Shipsey, Purdue U., presentation on cochlear implants

  16. Critical Bands & Pitch Determination • Can think of the 3.5-cm long Basilar Membrane as being divided into 10 regions of 3.5 mm each providing sensitivity to ~10 octaves. • The region of the basilar membrane excited by a pure tone of given frequency is wide: ~ 1.5 mm – “Critical Band”; region corresponds to just under 3 semitones (frequency range of about 18%), where 12 semitones = 1 octave. • “just-noticeable difference” = ~ 1/10th of a semitone (i.e., ~ 0.6% difference in frequency) • Interplay between physiological effects of signal sent to brain and signal processing by the brain are complicated and important!

  17. Slide from Ian Shipsey, Purdue U., presentation on cochlear implants The Copernican Revolution Von Békésy's findings stimulated the production of numerous cochlear models that reproduced the observed wave shapes, but were in contrast with psychophysical data on the frequency selectivity of the cochlea. displacement Davies (1983): a revolutionary new hypothesis there exists an active process within the organ of Corti that increases the vibration of the basilar membrane.

  18. Active amplification Careful measurements on living animal cochlea Same animal post mortem What causes the amplification? Johnstone et al (1986) Slide from Ian Shipsey, Purdue U., presentation on cochlear implants

  19. Rows of Hair Cells in the healthy cochlea Inner hair cells 10,000 afferent (signals go the brain) Outer Hair Cells 30,000 Sparsely innervated Hair 5m Hair cell 30m Slide from Ian Shipsey, Purdue U., presentation on cochlear implants

  20. Hair cells are mechano-electrical transducers 1980’s 500 nm Both inner and outer hair cells work this way 2nm diameter

  21. The inner hair cells send signals to the brain that are interpreted as sound. What do the outer hair cells do? Outer hair cells exhibit electro motility they are also electro-mechanical transducers 1987-2003 Slide from Ian Shipsey, Purdue U., presentation on cochlear implants

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