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Prof. Greg Francis1PSY 310: Sensory and Perceptual ProcessesPurdue UniversityAuditory PhysiologyPSY 310Greg FrancisLecture 29A dangerous device.Purdue UniversityHearing The sound stimulus is changes in pressure The simplest sounds vary in: Frequency: Hertz, cycles per second. How fast the pressurechanges Amplitude: decibels. How big a change there is. Complex sounds are made up of simple soundssuperimposed on each other Fourier analysis / synthesis Obviously, we do not hear all possible sound stimuliPurdue UniversityAuditory limits Different species are able to hear different frequencies ofsoundsPurdue UniversityAudibility curve Threshold forhearingvaries withfrequency Perceivedloudnessalso varieswithfrequencyPurdue UniversitySpecies variability Many animals can hear sounds at frequencies thatwe cannotPurdue UniversitySpeech sounds Speech sounds are an especially important stimulus They cover particular frequency ranges to which people arevery sensitiveProf. Greg Francis2PSY 310: Sensory and Perceptual ProcessesPurdue UniversityHearing loss As people age, their threshold intensity for hearing tends to goup Usually this is because of exposure to loud soundsPurdue UniversityiPods Unfortunately, people now listen to quit loud sounds fairlyoften And they turn up the volume in environments with loudsurrounding soundsPurdue UniversityHearing loss Worse still,hearing losstends to coverthe range offrequenciesthat includespeech No one “getsused” to anoisyenvironment,it means youare goingdeaf.Purdue UniversityAuditory system Basic anatomy of earPurdue UniversitySound stimulus Sound waves travel down the ear canal Hit the tympanic membrane (ear drum) It vibrates with the sound wavePurdue UniversityOssicles The tympanic membraneis connected to a smallbone Malleus Which connects toanother bone Incus Which connects toanother bone Stapes The end of the stapes Pushes against anothermembrane called theoval window, which is onthe cochleaProf. Greg Francis3PSY 310: Sensory and Perceptual ProcessesPurdue UniversityCochlea Spiral shape Filled with fluidPurdue UniversityCochlea Several membranes that divide it into separate compartments The round window pushes into one of these compartmentsPurdue UniversityCochlear chambers A cross-sectionview indicatesthe chambersof the cochleaPurdue UniversityCochlear membranes Special cells are located on the middle membrane to respondto movement of another membrane These membranes move in response to pressure from thestapes on the oval windowPurdue UniversityBasilar membrane This membrane contains the organ of CortiPurdue UniversityOrgan of corti Here’s another schematic The whole organ stretches along the entire membraneProf. Greg Francis4PSY 310: Sensory and Perceptual ProcessesPurdue UniversityOrgan of corti Here’s a electron micrograph Three rows of outer hair cells are visiblePurdue UniversityOrgan of Corti Three main components Tectorial membrane Sits on top Inner hair cells Outer hair cellsPurdue UniversityOrgan of Corti When sound hits the ear and the pressure istransferred to the oval window, the basilarmembrane moves Show animation This causes the haircells to bend Show animation Sound energy istransduced into anelectrical signal at thehair cellsPurdue UniversityHair cells Each hair cell has cilia that sticks up on top of the organ of corti They are arranged in a particular pattern 16,000 to 20,000 along the whole cochleaPurdue UniversityInner hair cells This is a electron micrograph of the top of a single inner hair cell The cilia pivot on their base in response to movement from thetectorial membrane, which is above themPurdue UniversityOuter hair cells This is a electron micrograph of the top of a single outer hair cell The tallest cilia are connected to the tectorial membrane, which isabove them. The smaller cilia are connected to their larger neighborProf. Greg Francis5PSY 310: Sensory and Perceptual ProcessesPurdue UniversityHair cells Movement of the tectorial membrane opens a“trapdoor” on the top of the cilia Normally, potassium ions stay outsidePurdue UniversityHair cells Movement of the tectorial membrane opens a “trapdoor” on thetop of the cilia With pressure, the trapdoors open and, potassium ions enter Animations Excitation Inhibition The potassium leads toneural responsesPurdue UniversityHearing loss Here’s another view of a healthy cochlea with normalhair cellsPurdue UniversityHearing loss Exposure to long-term loud noise can damage the haircell ciliaPurdue UniversityHearing loss Another comparison of a single outer hair cell Currently, there is no recovering from such damage It is permanent hearing loss An iPod (or whatever) played fairly loud can lead to this kind ofdamage If it’s too loud around you to hear your music, don’t listen Might be a good idea to keep the earbuds in (to block sound!)Purdue UniversityConclusions Anatomical structure and function of the ear Outer ear Middle ear Inner ear Cochlea Basilar membrane Organ of Corti Hair cells Hearing lossProf. Greg Francis6PSY 310: Sensory and Perceptual ProcessesPurdue UniversityNext time Responses to stimulus properties Frequency analysis Place


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Purdue PSY 31000 - Lecture 19

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