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PSYC 2390
Lana Trick

What is the Stimulus for Hearing? 11/4/2012 7:29:00 AM What is the stimulus for hearing? What is sound?  Sound is mechanical energy o Travels at around 340 m/s through air  Occurs when molecules bump up against each other  Air molecules bump into each other all the way into molecules in ear  Compression: molecules are close together than normal (dense, increase in air pressure)  Rarefaction: molecules are farther apart than normal (decreased density, causes slight decrease in air pressure  Plot normal air pressure vs. time o Go from having above normal air pressure (compression) to lower than normal air pressure (rarefaction) and back to above normal etc.  Measured in force per unit squared area o Force can be measured in dyne (force needed to accelerate 1 gram at 1 cm per second per second) Properties of a sound wave: Pure Tone: when pressure changes in the air occur in pattern described by mathematical function (sine wave)  E.g. flute, tuning forks  Rare in environment (normally more complex) Amplitude  Height of wave (half height of wave)  Corresponds to loudness of sound (volume) o Bigger the amplitude, the louder the sound  Softest sound we can hear is 0.0002 dynes/cm squared o If you have good hearing o Also known as sound pressure level (SPL) o Can hear a range of around 10 million sound intensities  Decibel (dB): created by Graham Bell created unit of loudness based on human abilities o How much louder sound is compared to softest sound we can hear o Uses logs to reduce magnitude of numbers from SPL o dB = 20 log [(actual sound pressure) / (sound pressure of softest sound we can hear)]  actual sound pressure P1 and softest sound is P0 o dB = 0  threshold of hearing  Normal breathing – 10 dB  Rustling leaves – 20 dB  2 person conversation – 60 dB  Busy traffic (beginning of danger level) – 70 dB  Vacuuming – 80 dB  Subway train – 100 dB  Concerts – 120 dB  Space launch (pain) - 180 dB  Decibels are physical measure whereas loudness is psychological Frequency  Related to idea of wavelength o Peak to peak  Wavelength and time o How many waves per second  Measured in Hz (wavelength per second)  Lowest key on piano – 27 Hz  Highest note on piano - 4186 Hz  Frequency is related as pitch (how high or low the sound is) o Low note – low frequency o High note – high frequency  Different species hear different ranges o Humans can hear from 20 - 20 000 Hz  Most sensitive to 2 000 – 4 000 Hz (speech frequencies) o Cats can hear higher frequencies but cannot hear some of the low frequencies that we can o Dogs can hear higher frequencies than us o Bats can hear even higher frequencies than us o Elephants can hear lower frequencies than us  Tone height: perceptual experience of increasing pitch that accompanies increases in tone‟s fundamental frequency  Tone chroma: notes with same letter (in music) sound similar o Going up octaves (tones separated by octaves have same tone chroma) o Tones with same chroma also have fundamental frequencies that are multiples of each other Audibility Curves  Plot dB vs. frequency in Hz  Have threshold of feeling (top, can become painful and cause damage to auditory system) and audibility curve (threshold for hearing, at bottom, anything below we cannot hear) Timbre  Most sounds we hear are not sine waves (like flute) o Most are complicated waves (not simple waves) o Have same loudness, duration and pitch but still sound different  difference is due to differences in timbre  Fourier analysis  any complex waves can be broken down into simple sine waves o Complex wave is sum of sine waves of different frequency, amplitude and phase angle o Ear is doing Fourier analysis by finding the simple sounds  Attack and decay o Attack  build up of sound at the beginning of the tone o Decay  decrease in sound at end of the tone o Harder to distinguish between two instruments when the first and last 1 ½ seconds are erased from recording / not heard  2 instruments playing the same note but sound different because they have differences in the mixture of frequency, amplitude and phase angle and missing harmonics Phase Angle  What point of the sound wave we are at  Plot normal atmospheric pressure o 0 degrees when you start o 90 degrees at peak of compression o 180 degrees back at zero o 270 degrees is peak of rarefaction and then back to zero again  Is it rarefaction time or is it compression time How does sound interact with… Objects  Echoes: bounces / reflect off the object o Bats make use of that (echolocation)  Sometimes sounds are absorbed by objects o Carpet absorbed about 25 % of sounds you have o Plaster and tile do not absorb as much (sounds are stronger)  Resonate o Every object has frequency at which it vibrates (resonate frequency) o Singing so loud can break glass  High clear sounds that makes molecules in glass vibrate so much that they shatter o Concert  Bones shake  you have reached resonance frequency  Bones can shatter o Everything has resonant frequency Other sounds  Can reinforce one another  put two sounds together and they get louder (makes amplitude larger) o Waves need to be at exactly the same frequency and same phase angle (go into rarefaction and compression at same time) in order for this to work  Can also cancel each other out o Take two sounds that are exactly the opposite phase (one is going into rarefaction at same time the other is going into compression you will get silence) o Active noise suppression  Can be places that cause reinforcement (sweet spot) and can have places that cause cancellation (dead zones)  Sounds can also alternate reinforcement and cancellation o Two tones (1000 Hz, 1004 Hz) o “Wow wow wow”  can hear because it is out of tune o Bands and tuning  Frequency is lower than it should be  flat  Frequency is higher than it should be  sharp Overview of the Functions of the Ear 11/4/2012 7:29:00 AM Overview of the Functions of the Ear  Hearing evolved from life in ocean o Lateral line: line of nerves  Had hairs sticking out in the water (sensors)  If something came near them, hair cells moved back and forth  Sense of hearing developed from this  Line of neurons with hair like cells that when water vibrates, hair cells vibrate and action potential produced  Moved ocean into ear  Need to gather the sound o Have orphases that are designed to tunnel sound in  Need to amplify sound o Impedance matching  Harder to run in water than in air (molecules in water are much closer together therefore harder)  Sounds can travel easily through air  Must get into fluid in head and must make fluid move  Must make sound more forceful (doesn‟t need to be forceful in air, needs to be forceful in fluid)  30 dB more forceful, must match the force needed  Need to have transduction o Change energy from mechanical energy into electrical energy  Need to perform frequency analysis o Literally do Fourier analysis  Decompose wave into constituent sine waves that produce it Physiology of the Ear 11/4/2012 7:29:00 AM Outer Ear: Pinnae  Floppy bits on outside  Channeling sound, gather sound together  Some animals can point their ears in direction of sound o Do this so they can gather sound o Some humans can do this (residual function)  Important in letting you know where the sound is coming from  Everyone has unique ear (shape) o Ear bounces sound in such a way that lets you know where the sound came from o If you changed the shape of ear, it would be hard for you to know where sound came from (used to how your ear channels sound Auditory Canal  2.5-3 cm long  Protective function (cold, pointy things (Q tip), contains ear wax)  Length causes ear to resonate to certain frequencies, this resonation auditory canal… o Amplifies frequencies of human speech (produces increase in intensity for 2000-5000 Hz, max intensity at 3400 Hz) o Determined partly by rigidity Ear Drum  A.k.a. tympanic membrane  Delicate membrane that vibrates to the sound (Also its problem)  Very soft sounds can make it move  Keeps structures in middle ear at relatively constant temperature Problems and Disorders  Plugged ear canal o Putting things in their ears or can be plugged with wax o Can‟t hear as well  Swimmer‟s ear o Get some fluid in ear and you don‟t quite get it all out o Fluid provides warm place for bacteria to grow o Very uncomfortable, itchy, can ache o Ear canal begins to swell and fluid gets trapped o Can take antibiotics  Broken ear drum o Loud sounds / explosions can break ear drum o Most common: Q tips o Ear drum will grow back  Never as good as it was before Middle Ear: on other side of ear drum, 2 cubic cm in volume Ossicles  3 tiny bones (2 names each), in order from closest to ear drum inwards, vibration from ear drum causes 3 bones to vibrate o Hammer  Malleus o Anvil  Incus o Stirrup  Stapes o 3 smallest bones in body o Help with impedance matching (sound travels much easier in air than in liquid of middle ear)  Must increase sound pressure  Stilettos  Concentrate force on small area (increases force)  Ear drum is large, bones are small  large force on small area  Leverage  Teeter totters (hooked in such a way that they provide leverage, concentrate force and make force more powerful so it can move fluid in inner ear) Eustachian Tube  Hooks together (channel) middle ear and throat  Air pressure can be different in middle ear than outer ear  Ears pop o As you go up in air, air pressure is lower in outer ear than middle ear  Ear drum is being stretched o Swallow so you have same pressure on either side of eardrum  Helps equalize pressure on either side of ear drum  Sometimes gets plugged (e.g. when you have a cold) o Can pop your ear drum and cause bleeding o Important to pop your ears Muscles of the Middle Ear  Attached to ossicles  Tensor tympani  Stapedius  Serve protective function o When experiencing really loud sounds, muscles condense / contract and pull stirrup away from inner ear and thus it is not shaking inner ear as much (acoustic replay) o Prevent damage of inner ear by dampening vibrations o Also protect from sound of chewing  Teeth are close to middle ear  Takes about 1/50 thof a second to work  When muscles are tired, ears are especially tired (competing for energy) o Ears are likely to be damaged when exercising to loud music Disorders of the Middle Ear  Otitis media o Occurs when infection creeps up Eustachian tube into middle ear from throat o Bacteria likes warmth  Begins to produce fluid when grows o Fluid basically produces pressure on ear drum (ear ache) and can burst ear drum  Even if you don‟t burst ear drum, can damage ossicles because they are gunged up o Children are likely to get because they have short Eustachian tubes o If happens repeatedly  can lead to cholesteatoma (development of scar tissue in middle ear, might require surgical removal to help hearing) o Worst case scenario: if infection passes into bone and possibly into brain (big problems)  Blood brain barrier  Lots of things in blood cannot pass into system  Brain does not have normal immune function o Treated with antibiotics, tubes to get rid of fluid, surgery  Otosclerosis o Hereditary o Bone growth that grows in around stapes that prevents stapes from moving o Causes deafness o Beethoven had otosclerosis o If person has, can sometimes have stapedectomy  Remove bone growth and are given artificial one instead Summary: Conduction deafness – Problems due to outer or middle ear:  Cannot hear because you cannot conduct sound o Shattered ear drum o By otitis media or otosclerosis o Plugging up auditory canal  Typically treat by increasing intensity of the sound (hearing aids) Inner Ear: Semi-circular Canals  Things that are involved in sense of balance  3 fluid filled chambers that have hair cells (nerve cells) o Designed for different kinds of motion  Pitch forward  Roll (side to side)  Yaw (twisting, rotary motion)  Problems in system might feel dizzy or nauseated Close up on the Cochlea 11/4/2012 7:29:00 AM Close up on the Cochlea Overview:  Size of bean, has fluid inside  Snail shaped tube  Stirrup pushes up against oval window o Causes fluid to move in cochlea and produces wave that travels down tube  Tube is divided into 3 parts o Vestibular canal o Tympanic canal  Perilymph (fluid, watery, in vestibular canal as well) o Cochlear duct  Endolymph (fluid, slimy, lot of potassium ions), if endolymph and perilymph are mixed up, will impair hearing  Round window (budges out when wave comes) Organ of Corti: 1. Reissner‟s Membrane  Very thin 2. Basilar Membrane  Supports organ of Corti and vibrates in response to sound 3. Tectorial Membrane  Extends over hair cells 4. Hair Cells  Inner hair cells (IHC) o Involved in pitch perception (whether note is high or low) o 3000 - 3500 per ear o Have cilia on them  Hooked together via actin fibers, in endolymph (lots of K+)  When there is a sound, causes fluid to move, causes trap doors in hair cells to open (blowing open screen door), potassium and some calcium influx into cell, causes an action potential due to depolarization  Causes release of neurotransmitters  Bending of opposite direction causes “trap doors” to close  Alternating bursts of electrical signals with no electrical signals  Pressure increases  cilia bend to right  firing occurs  Pressure decreases  cilia bend to left  no firing  Therefore hair cells fire in synchrony  Outer hair cells (OHC) o Placed in “V” shape o Helping role  cause basilar membrane to move up and down  Are hooked into basilar membrane o More than IHC o “cochlear amplifier”  What does the transduction (both) 5. Spiral Ganglia  Similar to retina ganglia  Receives message of neurotransmitters from hair cells  Type I o Have wide axon, therefore can send information really fast o Has to do this because it is sending information far (all the way up into the brain) o Involved in pitch perception o Inner hair cells connect with type I spiral ganglia o More abundant than type II (might be counter intuitive because we have more outer hair cells)  Type II o Narrow axon, information is not going very far, used in feedback loop  Ear  superior olive  tells ear what to do o Take information from outer hair cells and control what they do  Both go out the ear through the auditory nerve How do hair cells signal the pitch of a sound? 11/4/2012 7:29:00 AM How do hair cells signal the pitch of a sound?  How we know how high or low a note is Frequency Theory (Rutherford):  “Timing or Temporal Code” How is frequency signaled?  You get 100 action potentials per second for a 100Hz tone (100 waves per second)  Low number of action potentials per second  low sound  High number of action potentials per second  high sound  Can read Hz right off of action potentials Weak point for the theory…  A young adult can hear pitches of up to 20 000 Hz (dogs higher) o A neuron cannot produce 20 000 action potentials per second o Max. 500-800 action potentials per second produced by neurons  Therefore weak point is high sounds, good for low sounds (we can hear as low as 20 Hz)  Solutions to help theory: o Volley Principle  temporal coding  Cells take turns while the others are in various states of recovery  “volleys of fire”  Don‟t have to have every neuron firing for every
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