Psychology Of Sound

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Three Divivions of Ear

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OuterMiddleInner

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3 Parts of Outer Ear 

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PinnaAuditory CanalEardrum

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Auditory Canal 

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Tube leading into earAmplifies sounds arond 3000Hz

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Eardrum

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(tympanic membrane)passes vibrations on to the middle ear

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Three bones of the middle ear(ossicles)

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smallest bones in human bodysmalles muscles in human body (4)(In this order)Malleus (hammer)Incus (anvil)Stapes (stirrup)

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Oval Window

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stapes is attached to the oval windowsmall membrane that transmits vibrations to the inner ear

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What is the funciton of the middle ear and the ossicles?

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Impedence matching

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Impedence matching

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Inner ear is full of liquid and impedence of 30dB occurs. Ossicles act like a lever to amplify sound (3dB). Eardrum is 20x larger than oval window and funnels more force to oval window (recovers 23dB).For all of this to work, pressure in middle ear = outside air pressure

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Eustachian Tube

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Part of middle ear that allows for pressure between middle ear and outside air pressure to become equal for impedence matching

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Cochlea

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Inside inner earhollow cavity in the bone of the skullcoiled (spiral shaped)filled with fluidsize of pea

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Cochlear Base

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transmit higher frequenciesend of the cochlea closest to the oval window (where sound enters)

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Cochlear Apex

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transmit lower frequenciesend opposite of the cochlear base

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3 Chambers of the cochlea

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vestibular canal (oval window)cochlear ducttympanic canal (round window)

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Chochlear Membranes

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Reissner's Membrane - separates vestibular canal from cochlear ductBasilar Membrane - separates cochlear duct from tympanic membrane

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How sound travels throgh cochlea

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Oval window transmits vibrations to fluid in vestibular canalmovement of this fluid causes basilar membrane to movemovement of the round window compensates for pressure changes in the fluid of the inner ear

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Organ of corti

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sits on top of basilar membrane inside of the cochlear ductconsists oflayer of supporting cellshair cellstectorial membrane

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Hair Cells

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IHC - Inner hair cellsOHC - outer hair cells (cilia connected to tectorial membrane)top of both hair cells contain cilia

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IHC's

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3500 of themin a single rowrunning length of INNER part of the basilar membrane close to where tectorial membrane connects to wall of cochlear duct

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OHC's

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About 12,000Organized in 3-5 rows running length of the outer part of the basilar membranenot involved in transductiononly receive efferent infocauses cilia to elongate and contract which affect the mechanical vibrations of the membranes

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Transduction of Sound in the organ of corti

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Vibrations in fluid of cochlea cause basilar membrane to movecilia of IHC's bend - pulls open ion channelsIHC's release neurotransmitter into synapse with the auditory nerve fibernerve fibers fire and send info to brain

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Two Major Theories of Pitch Perception

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1. Frequency Theory (volley principle modification)2. Place Theory (2 Versions)

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Rutherford's Frequency Theory

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entire basilar membrane vibrates at the same frequency as the sound wavecauses hair cells to fire at this same ratewhich causes auditory nerve fibers to fire at this rateloudness coded by the number of neurons firingbigger amplitudes cause greater movement of basilar membraneresults in more hair cells being firedmore neurons = louder sound

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Rutherford's Frequency Theory(Support for)

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some auditory nerve fibers fire in synchrony with low frequency sounds(100Hz sine waves will cause some auditory nerve fibers to fire at 100x/sec)

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Rutherford's Frequency Theory(Problems with)

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1. Shape of the basilar membrane - thinner at base, thicker/wider at apex. cannot vibrate at a uniform rate over its entire length for all frequencies2. Refractory Period of Neurons - can't fire faster than 800-1000 times per second, however we can hear up to 20,000 Hz.

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Volley Principle (frequency theory mod)

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two or more fibers whose firing is offset in time can together signal higher ratesgroups of neurons cooperate to signal higher frequencies

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Volley Principle(Support)

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Phase locking: some individual auditory nerve fibers fire irregularly but always fire at same phase angle in the cycle of a sine wave. Therefore, large groups of neurons could signal any frequency.

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Volley Principle(Problems)

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Lower levels of the auditory system : Phase locking becomes very weak above 5,000 HzHigher levels of the auditory system: phase locking hasn't been found above 1,000 Hz.

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Place Theory (Helmholtz Resonance Theory)

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Thought that the basilar membrane was composed of individual fibers under tension, just like strings in piano.Different frequencies cause different fibers in different locations to vibrate(particular PLACE on the basilar membrane that is vibrating signals the frequency)ex. fibers at one place vibrate at 500Hz, while fibers at another only vibrate at 2000Hz 

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Place Theory (Helmholtz)(Problems)

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Basilar membrane is not composed of separate fibers that can vibrate individuallyBasilar membrane is slack, not under tension

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Place Theory(Bekesy)

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Sound waves create traveling waves that travel along the length of the Basilar membrane until it reaches a peak point of maximal displacementThe wave then dies out due to the shape and elacity of the membraneDifferent frequencies create a point of maximal displacement at different places along the basilar membraneCilia of IHCs at that particular place bend, causing the cells to fire and send signals to the auditory nerve fibers that synapse with it

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Tonotropic Organization of the basilar membrane

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Frequencies are represented along the basilar membrane in and orderly way acting like a frequency mapHigh frequencies cause maximal displacement near the baseLow frequencies cause maximal displacement near the apexLouder sounds create bigger amplitudes causing greater displacement of the membrane which causes more cilia to bend more, causing the cells to fire faster

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Place Theory (Bekesy's)(Support)

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 viewed traveling waves and single cell recordings show tonotropic organizationadjacent frequencies are represented in adjacent locations throughout the auditory systemstimulation of different auditory nerve fibers reulsts in perception of different pitchesfrequency tuning curves showed that different cells have differnt characteristic frequenciescharacteristic frequency depends on teh portion of the basliar membrane from which the nerve fiber recieves infoselective deafness where you often find deafness for only small range of frequencies and find damage to just one part of the basilar membrane

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Place Theory(Bekesy's)(Problems)

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with low frequency sounds, there's no real point of maximal displacement the whole membrane vibratesdifferent amplitudes can cause a shift in the point of maximal displacement with no corresponding shift in perceived pitch

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Evidence for and against both

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many believe that both frequency theory for perception of lower frequencies (approx 20Hz up to 1KHz) and place theory for perception of higher frequencies (approx 1KHz to 20KHz) may existphase locking (volley principle) may also play a role

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Missing Fundamental Frequency

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neither theory does a good job at explaining the effect of the missing fundamental frequency.effect must then occur in the brain rather than in the cochlea

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Timbre Perception

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Auditory system must perform something like a fourier analysis on complex tonesbasilar membrane codes the amplitueds and frequencies of all paritals that are presented simultaneously

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Auditory Pathways

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Auditory nerve relays info to nuclei (some nuclei deal with location, other's with identification)after traveling through several nuclei, the info reaches the Primary Auditory Cortextonotropic organization is found at all levels of the auditory system

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Primary Auditory Cortex 

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located within the temporal lobesfrom there information is relayed to other areas for additional processing and integration with other senses

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tonotropic organization of the auditory system

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cells at higher levels of the auditory system respond to more complex kinds of sounds

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Gestalt Psychology

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whole is greater than the sum of its partsdiscovered general principles used by our perceptual systems to group things into meaningful patterns

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Gestalt Principles

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1. Proximity - Objects near eachother tend to be percieved as a unit. (perceptually grouped togther)2. Similarity - objects similar to each other tend to be percieved as a unit.3. Good Continuation - objects arranged in a straight line or curve tend to be percieved as a unit4. Closure - when something has a gap, we tend to percieve it as a closed, complete figure.5. Common Fate - Objects that move together tend to be perceived as a unitthese principles apply to any property of music (pitch, loudness, duration, timbre, spatial location)

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Dichotic Presentation

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presenting each ear with different information

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Scale Illusion

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Ascending and Descending Scale in  dichotic presentationPerception of scale illusion is based on pitch proximity (gestalt's principle of proximity)

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Lateralization and Dominance with scale illusion

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Left dominant hempishere will hear high pitched melody on left and low pitched melody on left. And are also less likely to have unsual precepts (Right Handers).Right dominant hemisphere will equally hear high pitched melody on the the left or the right ear. And are also more likely to have unsual precepts.

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Tchaikovsky's Sixth Symphony

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two different themes whoes notes alternate between first and second violinseach instrument plays jumping pattern of notes with large intervalshowever, people perceive two smooth melodies with small intervals from each group of violins.Grouping based on pitch perception

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Phonemic restoration effect

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Gestalt's Principle of Good Continuationgaps in words or music are filled in with static and yet we percieve a smooth single tone without breaks or we can fill in the missing parts of speech to be able to understand

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Explanation for transformation precepts

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Hypothesis Testingbrain continuously tries to interpret the world, constantly searching for meaning. if more than one meaningful interpretation, brain tests alternative hypotheses.

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Melodic Stream Segregation

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In actual music, it's based on pitch proximity and we perceptually organize notes into different sections or melodic streamsphenomenon is frequently exploited by composerssolo instruments play counterpoint by rapidly alternating between notes in different pitch rangesrather than hearing a single melody that makes large jumps in pitch, we hear two  (or more) separate melodies in different pitch ranges 

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two factors that produce streaming

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1. Interval Size - larger the interval, the more likely streaming is to occur2. Spread of Presentation - the faster the presentation, the more likely streaming is to occur

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Top-Down Processing

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We use our knowledge to influence our perception of the world

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Bottom - Up Processing

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We absorb what we percieve through our 5 senses.