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
View Full Document