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66 Cards in this Set
- Front
- Back
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What is Sound, physically?
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- changes in pressure over time, transmitted through a medium - air or water
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Sources of Sound
- how is it produced |
- initiated by movement that disturbs air molecules
- molecules collied w/ each other - this results in changes in air pressure that spreads from the source |
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How Sound Propagates through the air
Tuning Fork example |
- Tuning fork gets struck
- Tine moves out (right)> collides w/ air molecules to right. Compressing molecules in section close together. - Tine moves in (more left than original)> Results in rarefaction, less than normal air pressure. - Time moves back out> collides w/ air molecules again, and pushes those molecules out further colliding into further out air molecules. |
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Definition:
Soundwave |
- Waves of pressure changes in air caused by vibrations of a source
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Definition:
Cycle |
In a soundwave, a repeating segment of air pressure changes.
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Definition:
INverse Square Law |
- Sound E on wave front decreases w/ distance from source.
- Falloff in Sound E w/ distance: Inverse Square Law - Sound decreases in proportion to square of the distance from source - Sounds at a distance are much quieter |
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3 Most Important physical dimensions of sound are:
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1) Frequency: pitch
2) Amplitude: loudness 3) Waveform: timbre (sound quality) |
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What is a Periodic Sound Wave?
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- Waves in which the cycles of compression and rarefaction repeat in a regular, or periodic, fashion.
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What is a Pure Tone?
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- simplest periodic sound wave
- sound wave which air pressure changes over time according to a mathematical formula called Sine Wave or Sinusoid - can be produced by an electronic signal generator and can be approximated by a flute |
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Definition:
Frequency |
The physical dimension of sound that is related to perceptual dimension of pitch
- expressed in hertz (eg. 1000 cycles/sec = 1000Hz) - number of cycles per second of a periodic sound wave |
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What is PItch?
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Perceptual dimension of sound that corresponds to physical dimension of frequency
- perceived highness or lowness of a sound. > HIgh pitch: piccolo > low pitch: tuba |
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What is the sound detection range for humans?
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20-20,000 HZ
- outside range, is inaudible to humans (no matter how loud) |
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What is Amplitude?
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- Difference between the Max and minimum sound pressure in a sound wave
- distance from peak to trough. - perceptual dimension of loudness |
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Define:
Loudness |
- Perceptual dimension of sound related to physical dimension of amplitude
- how intense or quiet a sound seems - also depends on frequency of sound and other factors |
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What are Decibels (dB)?
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Unit to measure sound amplitude; logarithmically related to sound pressure measure in micropascals.
- amplitude is measure in terms of sound pressure |
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What is:
dB SPL dB SPL = 20 log (p/p0) |
decibel sound pressure level
P0 is set at agreed-upon 20uPa, thus amplitude of a sound w/ pressure p = 20,000 uPa 20 log (20,000/20) = 20 log 1,000 = 20x3 = 60dB SPL |
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Calculating Decibels
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- 20 dB = 10x increase in sound pressure
- 100 dB = 100,000x more intense 20=20 log (p1/p0) 100=20 log (p1/p0) 1= log (p1/p0) 5=log (p1/p0) 10=p1/p0 100,000=p1 / p0 |
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Absolute Threshold for Hearing
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- Absolute threshold is the intensity of least intense sound that can be heard.
- not a single value - depends on sounds freq |
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Absolute Threshold for hearing
- experiment |
- psychophysical experiments
- P sits in sound attenuating chamber, w/ high fidelity speaker 2m in front of head, at ear level - chamber reduces outside noise - walls absorb sound waves, to reduce echoes - heartbeat is present - amplitude of tones, measure when taking P out, and placing mic where head was. |
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Audibility Curve
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Curve showing minimum amplitude at which sounds can be detected at each frequency
- audibility threshold at lower and higher freq that people can hear (20-20,000 hz) is greater that freq in middle range (500-5,000) - auditory sensitivity is max in this middle range, range of freq present in most human speech sounds. |
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Waveform
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- sounds produced by vibrations of objects such as vocal cords & clarinets - consist of multiple pure tones added together
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Waveform
- Fourier Analysis |
- Fourier Analysis: mathematical procedure for decomposing complex waveform into a collection of sine waves w/ various freq & amplitude
Eg) Fourier analysis shows complex waveform is sum of 3 sine waves. - Amplitude of complex waveform at any given time is sum of amplitudes-positive or negative- of the component wave at that time. |
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Waveform
- Fourier Spectrum |
A depiction of the amplitudes at all frequencies that make up a complex waveform
- each sine wave is represented as a vertical line, single freq w/ a given amplitude |
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Waveform
- Fundamental Frequency |
- Frequency of the lowest-freq component of the complex waveform
- determines the perceived pitch of the sound. |
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Waveform
- Harmonic |
- Each component of a fundamental spectrum is called a harmonic
- first harmonic is the fundamental freq, 2nd harmonic is next lowest-freq component, and so on. - 2nd & higher harmonics also called: overtones - 2nd & higher harmonics are integer multiples of the fundamental freq. eg) fundamental freq of the note A880 produced by clarinet is 880Hz, - 2nd harmonic is 880x2=1760Hz, - 3rd harmonic is 880x3= 2640 |
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Waveform
- what is Timber? |
- Two complex sounds that have same pitch & loudness, but dont sound the same.
- difference in sound quality between two sounds - for complex periodic sounds, timbre is due to dif in relative amplitudes of sounds overtones - perceptual dimension of sounds is that is related to physical dimension of waveform - low amplitude overtones contribute less to timbre than high-amp overtones |
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Differences in Timbre
Flute vs Violin |
- Flute spectrum is dominated by first 2-3 harmonics, give flute a sound quality closer to that of a pure tone
- Violin has significant E at many of the higher harmonics, giving the violin a "richer" sound quality - diff in relative amplitudes of harmonics are what give each sound its distinctive timbre. |
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What happens if only the fundamental freq is remove, without removing any other harmonics?
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- There is a diff in sound quality
- pitch of the sound seems to be same as before, even though the fundamental freq, which determines the pitch of a complex periodic sound, isn't present. - Called Illusion of Missing Fundamental |
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The Ear
- What is it, and what does it do? |
- Peripheral part of auditory system
- Transduces sound into neural signals - divided into: outer, middler, and inner ear |
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Outer Ear
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3 parts
- Pinna, auditory canal, Outer surface of Tympanic Membrane - Function: outer ear funnels sound onto tympanic membrane - which vibrates in response to sound waves. > vibes are transmitted into middle ear. |
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Outer Ear
- Pinna |
Outermost portion of ear
- shaped like funnel to direct sound into ear canal - aids in sound localization |
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Outer Ear
- Auditory Canal |
- Narrow channel that funnels sound waves gathered by Pinna onto tympanic membrane
- amplifies freq in the range of 2000-5000 Hz |
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Outer Ear
- Tympanic membrane |
aka; eardrum
- thin, elastic diaphragm forms seal between outer & mid ear - vibrates in response to sound waves that strike it. |
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Middle Ear
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- responsible for amplifying and transmitting sound signal between outside air (eardrum) and inner ear (oval window)
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Middle Ear
- Ossicles |
Three smallest bones in the body
- transmit sound E from tympanic membrane to inner ear 3 Bone: - Malleus (or hammer), Incus (or anvil), Stapes (or stirrup) - bones are connect to one another, malleus is connected to tympanic membrane> when tym. membrane pushes on the malleus, malleus pushes on incus, displaces stapes, pushes on Oval Window> sends vibration to cochlea (liquid chamber) |
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Middle Ear
- ossicle anatomical advantages |
1) Tympanic membrane is 15-20x larger than Oval Window.
- sound E collected by tymp mem is concentrated on smaller area, amplifying effect! 2) Ossicles produce lever action - small movement at Malleus (near axis point), causes large displacement of the stapes (moment) - magnifies vibrations > these two characteristics can amplify sounds in air by 20-30dB |
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Middle Ear
- Acoustic Reflex |
- reflex contractions of 2 tiny muscles in ear
- responds to high intensity sounds - dampens movements of ossicles, helps protect auditory system from damage due to loud noises - Limited capacity, responds to lower freq. - vulnerable to loud high-freq noise - Also takes more than 1/10th of sec to occur, too slow for brief high-intensity sounds |
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Middle Ear
- Eustachian Tube |
Tube connecting the mid ear and top part of throat; normally closed but can open briefly (yawning, swallowing) to equalize air pressure in mid ear w/ air pressure outside.
eg) airplane or tall elevator, - Unequal air pressure when going up tall bldg - air pressure outside tymp mem goes down - air pressure in mid ear doesn't change - greater pressure on inner ear, makes membrane stretch, dampens vibrations> causes muffling sound. |
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Inner Ear
- Cochlea |
- Snail shaped compartment
- has 3 chambers: Vestibular canal, Cochlear duct, Tympanic Canal - Reissner's membrane separates chambers |
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Inner Ear
- Cochlear duct & organ of Corti |
- one of three chambers in cochlea
- resting on basilar membrane w/ in cochlear duct is Organ of Corti> responsible for auditory transduction - Cochlear duct is filled w/ endolymph, fluid that facilitates auditory transduction - Organ of Corti contains hair cell receptors |
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Inner Ear
- Vestibular & Tympanic Canals |
- chambers of cochlea
- both filled w/ perilymph, fluid similar to CSF. - perilymph carries vibrations through cochlea |
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Inner Ear
- Semicircular Canals |
1) Vestibular system
- sense organs used to produce neural signals carrying info about balance and acceleration; includes semicircular canals and otolith organs 2) semicircular canals - part of vestibular system; perpendicular hollow curved tubes in skull, filled w/ endolymph, responsible for signaling head rotation. |
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Organ of Corti
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- w/in cochlear duct
- rests on basilar membrane - responsible for auditory transduction - 3 components: two sets of neurons: - Inner Hair Cells and Outer Hair Cells, and Tectorial Membrane |
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Hair Cells
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- One row of 3,500 inner hair cells
- 3 rows of 12,00 outer hair cells total > Outer hair cells are cylindrical, stereocilia are attached to tectorial membrane, amplify and sharpen responses of inner hair cells, 5% of auditory nerve fibres > Inner Hair cells: are pear shaped, tips of inner h.c stereocilia float free in endolymph, Inner h.c responsible for tranducing sound into neural signals, 95% of auditory nerve fibers |
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Tip Link open ions channels on
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a) bending of hair cell stereocilia increases tnesion on the tip links connecting them
- tip links pulls open channel, positively charged Ca & K ions enter hair cell |
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What do outer hair cells do?
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- depol of cell membrane results in change in shape of protein, called prestin in the membrane
- shape change causes cell body and stereocilia to execute physical movements similar to stretching & contracting - motile response > changes in length of outer H.C, magnify movements of basilar membrane in regions w/ characteristics freq corresponding to freq in the sound> means inner HC in those regoins send stronger signals in response to sound> motile response amplifies sound > Magnified movements ocur in narrow regions of bas membrane, means iiner HC send more signals that are more freq specific - motile response sharpens response to freq in sound |
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Basilar Mmebrane & Neural encoding of pitch
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- pitch is the psychophysical counterpart of freq
- 2 major theories of how vibration affects the basilar membrane and the encoding freq (pitch) > which fibres are responding - Place Theory - specific groups of hair cells on basilar membrane activate specific set of nerve fibers (guitar string) > How fibres are firing- freq theory at Temporal code - rate or pattern of firing of nerve impulses |
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Code of Pitch: Place Theory
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- Suggests that diff freq disturb diff regions of bas. membrane (ie, diff cells)
- Helmhotz proposed "resonance" theory > bas mem. wider at apex > suggested fibers in bas mem resonated at diff freq at diff locations along its length (long fibres at apex, short at base) - Problem w/ resonance theory > no fibers > not under tension |
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Psychophysical Tuning Curves
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>experimental procedure
- First, a low level test tone is presented - Then, masking tones are presented w/ freq above & below test tone - Measures are taken to determine level of each masking tone needed to eliminate perception of test tone - Assumption is that masking tones must be causing activity at same locations as test tone for masking to occur - common neural mechanism > Resulting tuning curves show that the test tone is affected by a narrow range of masking tones > Psychophysical tuning curves show the same pattern as neural tuning curves which reveals a close connection between perception and the firing of auditory fibers. |
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Evidence for Place Coding
- Stimulation Deafness Experiments |
- expose animals to high amplitude tones of a particular freq & examine which hair cells are damaged
- Low freq causes damage to cells near the end > damage to relatively broad area - High freq causes damage to cells near stapes > damage to relatively narrow area |
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Frequency Theory (Temporal Code)
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- Proposes the basilar membrane vibrates in synchrony w/ the pressure changes (at the same freq as the sound)
- Freq representation based on a match between the freq in incoming sound waves and the firing rate of auditory nerve fibers - Similar to a diaphragm in a speaker > vibrates as a unit > results in impulses in the auditory nerve at same freq as sound itself - Two Problems: > bas membrane not like a diaphragm > nerve fibres can't fire above 1000 Hz |
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Problems for theories of the encoding of Pitch
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- loudness
- changes in pitch perception in noise - missing fundamental |
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Loudness & pitch
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- as the intensity of tone changes, so does the pitch
- low freq tones - high intensity sounds appear lower in pitch - high freq tones - high intensity tones appear higher in pitch |
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shifts of pitch in noise
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- tones heard in background noise - pitch appears to be shifted in direction opposite to the pitch of the noise
> tone in lower freq noise appears high in pitch > tone in noise higher in freq appears lower in pitch |
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The missing fundamental
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- most natural sounds have a fundamental freq and harmonics, which are always some multiple of the fundamental
- the defining characteristic of the sound is the fundamental - the missing fundamental phenomenon occurs when only the higher harmonics of a tone are presented - In this situation, the fundamental is still heard - Poses problems for a simple place theory |
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Pitch encoding
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- Is pitch encoded according to place or freq theory?
- likely a combination of both of these theories accounts for our perception of pitch - but there is also evidence for a role of auditory cortex in the perception of pitch as well |
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Loudness Perception (amplitude representation)
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Firing rate = freq x amplitude
- a similar "principle of univariance" in colour vision Dynamic Range - the range of amplitudes that can be heard and discriminated when applied to an individual nerve fiber, the range of amplitudes over which the firing rate of the fiber changes |
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Hearing Impairment
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- decrease in a persons ability to detect or discriminate sounds compared to a healthy young adult
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Tinnitus
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- persistent perception of sound in one's ears, ringing or buzzing.
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Myths about Deafness
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- deaf people can't hear anything
- hearing aids "cure" deafness - deaf people can't talk - deaf people are less intelligent than hearing people - all deaf people can read lips - deafness (or hearing impairment) is not just a simple reduction in auditory sensitivity - its not just having permanent ear plugs |
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Audiometer
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- instrument that tests peoples hearing
- presents pure tones w/ known freq and amplitude to right or left of ear - Audiologis uses staircase method to estimate persons absolute threshold for each 6-8 frequencies, ranging from 250-8,000 Hz - need to take into acct freq & intensity - represents amt of hearing loss compared to normal (audiometric zero) |
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Audiogram
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Graphical depiction of auditory sensitivity to specific freq, compared to sensitivity of a standard listener. Used to characterize possible hearing loss
- can reveal the kind of hearing loss present: degree of hearing loss in dB Hearing is measure under diff conditions - air or bone conduction air conduction: > a sound goes through mid-ear bone conduction: > sound bypasses mid ear - Masked or unmasked > masking ensures that only one ear can hear the test tone |
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Forms of Hearing Loss
-2 types |
> Conductive hearing impairment
- outer or mid ear - usually overall reduction in sensitivity > Sensory/neural loss - inner ear or auditory neurons - may show loss over entire range of audible freq or selective loss |
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Conductive Hearing Impairment
Mechanical impediment |
> common causes:
- blockage in external ear - otitis media (infection) - otosclerosis - punctured eardrum Diagnosis - similar bone and air thresholds - typical high freq loss Treatment: - advanced stage, replacing stapes - cochlear implants - not considered profound (loss of 90dB or >) Sound can till be conducted to cochlea via vibrations in bones |
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Sensori-Neural Loss
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Hearing impairment caused by damage to cochlea, auditory nerve, or auditory areas or pathways of the brain
Common Causes: - age, noise, ototoxic (drugs) Diagnosis: - similar bone and air thresholds - loss may be profound Treatment: - hearing aids - cochlear implants |
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Prebycusis
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- age related hearing impairment
- life long exposure to noise - long exposure to: drugs, chemicals, diabetes, CV disease, head trauam - greater in men than women |
