Textbook Notes (362,902)
Canada (158,096)
Psychology (9,565)
PSYB51H3 (301)
Chapter 9

PSYB51 CH. 9.doc

10 Pages
Unlock Document

University of Toronto Scarborough
Matthias Niemeier

Ch. 9- Hearing: Physiology & Psychoacoustics • fundamental human ability= communication through speech • fundamental sound qualities: loudness + pitch • sound created when object vibrates--> vibrations cause molecules in the object's medium to vibrate= pressure changes (waves) in the medium=wave becomes less prominent as it moves farther away • sound waves travel at a particular speed depending on the medium= move faster through denser substances (340 m/sec in air vs. 1500 m/sec in water) • light waves moves through the air almost a million times faster than sound= lag time between seeing and hearing thunder • Basic Qualities of Sound Waves • sound waves we hear= fluctuations in air pressure across time • amplitude/intensity= magnitude of displacement (increased/decrease) of a sound pressure wave= difference between highest and lowest pressure area ◦ perceived as LOUDNESS in hearing vs. BRIGHTNESS in vision ◦ height of the wave ◦ inc. Amplitude= inc. Loudness ◦ measured in dB (decibels)= a unit of measure for the physical intensity of sound= defines the difference between 2 sounds as the ratio between 2 sound pressures = 20 log (p/p0) where variable p is the pressure/intensity of the sound being described and p0 is a constant ▪ relatively small decibel changes can correspond to large physical changes • frequency= the number of times per second that a pattern of pressure change repeats (number of wavelengths/cycles per second) ◦ measured in Hz (hertz)= a unit of measure for frequency, one hertz is one cycle per second ◦ perceived as PITCH ◦ wavelengths in light= colour ◦ lower freq = lower pitch (tuba) ◦ human hearing= limited range of frequency (20 to 20,000 Hz) • Sine Waves and Complex sounds • sine wave/pure tone= simplest kind of sound, a waveform for which variation as a function of time is a sine function ◦ all sounds are composed of sine waves • complex sounds are best described in a spectrum (representation of the relative energy/intensity present at each frequency) ◦ harmonic spectra= spectrum of a complex sound in which energy is at integer multiples of the fundamental frequency ▪ typically caused by a single vibrating source (string of guitar/reed of a sax) ▪ each frequency component= a “harmonic” ▪ first harmonic= fundamental frequency= the lowest freq. Component--> all other harmonics have frequencies that are integer mulitples of this harmonic ◦ Shape of a spectrum= important quality that distinguishes different soundes ▪ can help identify sound sources--> spectra from different instruments will have diff shapes (different patterns of amplitudes for each harmonic) ▪ timbre= psychological sensation by which a listener can judge two sounds with the same loudness and pitch dissimilar. Timbre quality is conveyed by harmonics and other high frequencies. Quality of sound that depends, in part, on the relative energy levels of harmonic components • Basic Structure of the MammalianAuditory System • Outer Ear • outer ear= external, sound-gathering portion of the ear, consisting of the pinna and the ear canal ▪ pinna= the outer, funnel-like part of the ear ▪ sounds first collected from the environment here= typically called the ear ▪ only mammals have pinna (vary in shape and size between species, less within species) ▪ pinna--> ear canal= canal that conducts sound vibrations from the pinna to the tympanic membrane and prevents damage to the tympanic membrane = extends 25mm into the head ▪ pinna--> ear canal--> tympanic membrane= ear drum= a thin sheet of skin at the end of the outer ear canal= vibrates in response to sound (pressure change of sound waves) • painful to rupture tympanic membrane, but often it will heal itself • border between outer and inner ear • Middle Ear ◦ middle ear= an air-filled chamber containing the 3 tiny middle bones/ossicles= conveys and amplifies vibrations from the tympanic membrane to the oval window ◦ ossicles= malleus, incus, stapes= 3 bones of the inner ear that amplify sound waves= smallest bones in the human body= amplify sound vibrations in 2 ways 1. work like levers= a modest amount of energy one side becomes larger on the other= increases amount of pressure by about a third 2. ossicles increase energy transmitted to inner ear, by concentrating energy from a larger surface to a smaller surface= oval window is about 18X smaller than the tympanic membrance = 18X magnification of pressure **important because takes more energy to move liquid than it does to move air= sound would not be able to move the fluid-filled chambers of the inner ear without this magnification= would just bounce back of the oval window ▪ malleus= connected to the tympanic membrane and the incus= incus= connects the malleus and the stapes= stapes= third ossicle, pressed against the oval window, transmits the vibrations of the sound waves to the oval window ▪ pinna--> ear canal--> tympanic membrane--> malleus--> incus--> stapes--> oval window= flexible opening to the cochlea through which the stapes transmits vibrations to the fluid inside • oval window= border between middle ear and the inner ear **ossicles play an important role in LOUD sounds too= middle ear has 2 muscles (smallest muscles): 1. tensor tympani= attached to the malleus= tensing this muscle decreases vibration 2. stapedius= attached to the stapes= tensing this muscle decreases vibration ** main purpose= ACOUSTIC RELEX= tense when sounds are very loud, restricting the movement of the ossicles and thus muffling pressure changes that might bthlarge enough to damage the delicate structures in the inner ear= follows onset of loud sounds by 1/5 of a second= helps in sustained loud sounds but not abrupt ones (ex. Firing of a gun)= also tense during swallowing, talking, general body movement helping to keep auditory system from being overwhelmed by sounds generated by our own body • Inner Ear ◦ here fine changes in sound pressure available in the environment are translated into neural signals that inform the listener ◦ function of inner ear= analogous to that of retina with respect to light waves= translates the info carried by waves into neural signals ◦ major structure= cochlea= a spiral structure of the inner ear containing the organ of Corti ◦ cochlea is filled with water fluids in three parallel canals ▪ tympanic canal= one of three fluid-filled passages in the cochlea. Extends from the round window at the base of cochlea to the helicotrema at the apex ▪ vestibular canal= extends from oval window at the base of the cochlea to the helicotrema at the apex ▪ middle canal= sandwiched between the tympanic and vestibular canals= contains the cochlear partition **tympanic canal and vestibular canal are effectively wrapped around the middle canal **helicotrema= opening that connects the tympanic and vestibular canals at the apex of the cochlea ◦ 3 canals of the cochlea are separated by two membranes ▪ Reissner's membrane= between the vestibular canal and the middle canal ▪ basilar membrane= between the middle canal and tympanic canal= not really a membrane (unlike tympanic membrane, oval window or Reissner's membrane) b/c its a plate made up of fibres that have some stiffness • basilar membrane= forms base of the cochlear partition • cochlear partition= a complex structure through which sound waves are transduced into neural signals= made up of the basilar membrane, tectorial membrane and organ of Corti **vibrations transmitted through the tympanic membrane and middle-ear bones (malleus, incus, stapes), cause the stapes to push and pull the flexible oval window in and out of the vestibular canal at the base of the cochlea--> movement of the oval window causes waves of pressure changes, called “travelling waves” to flow through the fluid into the vestibular canal--> “ bulge” forms in the vestibular canal because its a closed system--> “ bulge travels from the base of the cochlea down to the apex--> by this time the traveling wave's displacement has mostly dissipated **IF sounds are extremely INTENSE= any pressure that remains is transmitted through the helicotrema (opening that connects the tympanic and vestibular canals at the apex of the cochlea) and back to the cochlear base through the tympanic canal---> absorbed by stretching the round window= soft area of tissue at the base of the tympanic canal that released excess pressure remaining from extremely intense sounds ** vestibular and tympanic canals are wrapped tightly around the middle canal--> when the vestibular canal bulges out, it puts pressure on the middle canal which DISPLACES the cochlear partition lying at the bottom of the middle canal--> the moves the partition down as the vestibular bulge comes through and back up as the bulge passes by • Organ of Corti- structure on the basilar membrane (btwn the middle and tympanic canals, forming the base of cochlear partition) of the cochlea that is composed of specialized neurons called hair cells and dendrites of auditory nerve fibres that terminate at the base of the hair cells and a scaffold of supporting cells= translates movements of the cochlear partition into neural signals ◦ hair cell= any cell that has stereocilia for transducing mechanical movement in the inner ear into neural activity sent to the brain= some hair cells also receive input from the brain ◦ auditory nerve fiber= collection of neurons that convey info from hair cells in the cochlea (afferent) to and from the brain stem (efferent) ◦ hair cells in each human ear are arranged in four rows that run down the length of the basilar membrane= 1 row of inner hair cells and 3 rows of outer hair cells ◦ inner and outer hair cells= foundation for stereocilium= any of the hairlike extensions on the tips of hair cells in the cochlea that, when flexed, initiate the release of neurotransmitters ◦ inner hair cells= stereocilia arranged in several nearly straight rows with the shorter stereocilia in front and the taller ones peering over their shoulders ◦ outer hair cells= stereocilia stand in rows that form the shape of a V/W ◦ tectorial membrane= gelatinous structure attached on one end, that extends into the middle canal of the inner ear, floating above inner hair cells and touching outer hair cells= extends atop the organ of Corti= because its attached at only one end, it SHEARS across the width of the cochlear partition whenever the partition moves up/down= shearing motion in turn causes the stereocilia of both inner and outer hair cells to bend back and forth • like photoreceptors in the retina, hair cells= specialized neurons that transduce one kind of energy (sound pressure) into another form of energy (neural firing)--> deflection of a hair cell's stereocilia causes a change in voltage potential--> initiates release of neurotransmitters--> encourages firing by auditory nerve fibers that have dendritic synapses on hair cells **differences between photoreceptors and hair cells that is most interesting • retina= 100 mill. Photoreceptors VS. Cochlea= only 14,000 hair cells ◦ stereocilia is better when it comes to speed and sensitivity ◦ sensitivity= shortest stereocilia are in front of slightly taller stereocilia etc.= each stereocilium is connected to its taller neighbour by a tip link (a tiny filament that stretches from the tip of a stereocilium to the side of its neighbour) so the stereocilia connected by tip links bend together as a set when deflected by the shearing motion of the tectorial membrane ▪ stereocilium deflects= tip link pulls on the taller stereocilium= opens an ion pore= permits potassium ions (K+) to flow INTO the hair cell= rapid depolarization= influx of Ca2+= initiation of release of neurotransmitters from base of the hair cell= stimulates dendrites of the auditory nerve ▪ MET (MECHANOELECTRICALTRANSDUCTION)= opening of ion pores that results from direct connection between stereocilia via tips links is the only example of MET= responsible for both extreme speed and sensitivity of hair cells= depolarization does not await a cascade of biochemical processes (speed) and ion pores open when deflection is as little as 1 nm (sensitivity) **OVERVIEW air pressure wave is funnelled by the pinna--> auditory canal--> tympanic membrane/ear drum= vibrates--> moves malleus, moves incus, moves stapes (middle-ear)--> pushes and pulls on the oval window--> pressure bulge moves down the length of the vestibular canal--> displaces middle canal up and down--> up and down motion forces the tectorial membrane to shear across the Organ of Corti--> moves stereocilia atop hair cells--> initiates rapid depolarization--> release of neurotransmitters into synapse between hair cells and dendrites of auditory nerve fibers--> initiate action potentials in the auditory nerve fibers--> brain • Coding of Amplitude and Frenquency in the Cochlea • increase amplitude--> increase bulge in the vestibular canal--> cochlear partition moves farther up and down--> tectorial membrane shears across organ of Corti more forcefully--> hair cells bend farther--> more neurotransmitters to be released--> action potentials fire more quickly ◦ larger the amplitude= higher the firing rate of the neurons • cochlear partition is displaced up and down in a pattern reflecting the pattern/frequency of the sound waveAND different parts of the cochlear partition are displaced to different degrees by different sound wave frequencies ◦ high frequencies= displacements closer to the oval window, near the base of the cochlea ◦ low frequencies= displacements close to the apex of the cochlea ◦ place code= turning of different parts of the cochlea to different frequencies, in which info about the particular frequency of an incoming sound wave is coded by the place along the cochlear partition that has the greatest mechanical displacement ◦ caused greatly by the way the structure of the basilar membrane (between middle and tympanic canal= base of the cochlear partition) changes along the length of the cochlea---> cochlea as a whole narrows from base to apex BUT basilar membrane WIDENS towards the apex (becoming thinner as it widens)--> results in cochlea separating frequencies along its length like an acoustic prism ▪ high frequencies bend the narrower- stiffer regions of the basilar membrane near the base ▪ lower frequencies bend the wider regions near the apex • Active Process Sharpen Tuning to Frequency ◦ inner vs. Outer hair cells ▪ about 90% of afferent (neurons that carry sensory info to the CNS/Brain) fibers in the auditory nerve, synapse on the INNER hair cells--> convey sound TO the brain ▪ most nerve fibers that synapse with outer hair cells are efferent (carry info from the CNS/brain to the periphery)= when these efferent fibers become active, outer hair cells with which the synapse become longer making nearby cochlear partition stiffer= by making some parts of the cochlear partition stiffer= outer hair cells make cochlea more sensitive and sharply tuned to particular frequencies **INNER=AFFERENT, OUTER= EFFERENT • TheAuditory Nerve • cochleabrain • responses of individualAN fibers to different frequencies is related to their place along the cochlear partition due to: ◦ inner hair cells (on which most afferentAN fibers synapse) extend along a line traveling the length of the cochlear parition + ◦ sounds with different frequencies displace different regions of the cochlea • SO different fibers selectively respond to different sound frequencies • frequency selectivity is clearest when sounds are very faint= at very low intensity levels, anAN fiber will increase firing to onl a very restricted range of frequencies • threshold tuning curves= a graph plotting the thresholds of a neuron/fiber in response to sine waves with varying frequencies at the lowest intensity that will give rise to a response= shows how intense the sine waves of different frequencies must be for the neuron to fire faster than its normal firing rate • characteristic frequency (CF)= the frequency that increases the neuron's firing rate at the lowest intensity (lowest point on the threshold tuning curve) • Complications: almost all sounds are more complex than simple sine waves and most sounds are much louder than the very quiet sound waves used to measure thres
More Less

Related notes for PSYB51H3

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.