Sound and hearingProf. Tom C.T. YinDept. of PhysiologyNeuroscience Training ProgramWhat is sound? Common wavelengthsf = 100 Hz λ≈ 3 mf = 1000 λ ≈ 30 cmf = 2000f = 2000λλ ≈≈ 15 cm 15 cmf = 10000 λ ≈ 3 cmSound is a mechanicaldisturbance propagated throughan elastic medium as alongitudinal traveling wave. Itobeys the wave equation, i.e. forwavelength λ and frequency fλ = c/fwhere c is speed of sound (~330m/s or .2 miles/sec in air)Time1/fλHuman psychophysics Psychophysics is the study of the relationshipbetween stimuli and their subjective correlate,or perception. The physical parameters of frequency andintensity are associated with thepsychophysical properties of pitch andloudness. The absolute threshold of detection is astandard psychophysical measure. At the human threshold, the pressure differencesare ~10-9 of atmospheric pressure! The air vibrations at threshold are ~0.1 of atomicdiameters!!Human audiogramFourier analysis:decomposing complex soundsFrequencyanalyzerAmpl.10753 dB3 dBdB = 20*log(P1/P2)Parts of the earBear et al., 2001Middle ear and inner earBear et al., 2001Middle ear ossiclesFS = FTMPS*AS = PTM * ATMPS/PTM = ATM/AS, pressure amplification of ~20StapesTympanic membraneStructure of the inner earPurves et al., 2001Width of basilar membrane changesfrom base to apexBear et al., 2001Pressure wave conduction in inner earKandel et al., 2000Basilar membrane is tonotopicallyorganizedBear et al., 2001Traveling wave on basilar membraneto sinusoidal tonevon Bekesy, 1960Maximum displacement for this particular frequencyCochlear traveling wave Courtesy Lloyd WattsBasilar membrane: traveling waveOne signal in, 3 components outKandel et al., 2000Transduction in hair cells of the auditoryand vestibular systemsAuditory nerve fiber responsesFrequency tuning Responses to tonesPurves et al., 2001Irvine, ANFs arenarrowlytuned infrequencyLow CF ANFsfollow thetemporalwaveform, i.e.,phase lock totonesThe Outer EarSome of the videos shown in this talk are based on “Auditory Transduction”by Brandon Pletsch which was awarded 1st place in the NSF/AAAS Scienceand Engineering Visualization Challenge 2003. Video edited by S. Lichti .Courtesy Prof. Ian ShipseyTympanic vibrationsThe tympanic membrane and ossicles1543AnatomistAndreas Vesaliusdescribes thestructure of themiddle ear.The tympanic membrane and ossiclesThrough the ossicles the vibration of the tympanic membrane is transmitted to the stapesBony labyrinth, stapes and round windowThe bony labyrinth, cochlea and its chambers1561 Gabriello Fallopiodiscovers the snail-shapedcochlea of the inner ear.The cochlea is about the size of a peaThe cochlea houses the Organ of CortiAuditoryNerveOrgan of Corti1st detailed study of Organ of Cortiby Alfonso CortiOriginal figures (scanned) from: Zeitschrift für wissenschaftliche Zoologie (1851)Hair Cells are a mechano-electric transducerThe basilar membrane is a frequency analyzerTonotopic OrganizationPhase-locking of auditory nerve fibersInnervation of IHCs and OHCsThere are two kinds of hearing loss Conductive hearing loss Sound information cannot reach the inner ear Commonly caused by middle ear infections Sensorineural hearing loss Abnormalities in the cochlea or in the brain Commonly caused by loss of hair cellsHair cell loss due to noise damageNormalGood song Good talkFollowing noisedamageBad song Bad talkCochlear implant facts First approved by FDA in 1985 and for children in1990. It is the first and most successful BMI to date. Worldwide, over 40,000 patients from age 1 to 80years old have received implants. Miss America of 1995, Heather Whitestone, deafsince infancy received an implant in 2002. Cost of CI ~$60,000 each; Medicare will pay for$20K; some insurance companies will pay the rest,others will not Surprisingly, perhaps, the most resistance toimplants comes from the deaf community.1. Sounds are picked up by amicrophone and sent to a speechprocessor where the spectrum isanalyzed and “coded” (turned into aspecial digital pattern of electricalpulses).2. These pulses are sent to a coilantenna, then transmitted acrossthe intact skin (by radio waves) to areceiver in the implant.3. The implant reads the program andfollows the instructions sending apattern of analog electrical pulses tomultiple electrodes in the cochlea.4. The auditory nerve picks up theelectrical pulses and sends them tothe brain.5. The brain recognizes the signals assound.Unlike hearing aids, which makesounds louder, a Cochlear Implantbypasses the non-functional haircells of the ear and delivers weakelectrical signals directly to theauditory nerve.Cochlea ImplantCochlear implant systemtimeamplitudeAmplitudeCurrent Multiple electrodesat separate locationsexploit the tonotopicarrangement of thecochleaCochlear implant can restore some hearingdespite hair cell lossSpectrograms of speech soundsAuditory nerve fiber responses to speech sounds1-1-channelchannel2-2-channelchannel4-4-channelchannel8-8-channelchannel16-16-channelchannelOriginalOriginalSpectral Resolution (Number of Channels) StudyImplant simulations by Arthur Boothroyd, based on the work of Robert ShannonLike VoltaThe limited number ofchannels affects pitchperceptionMusic – 8 channelOriginal
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