Hearing Sciences Final

Transient Sounds

- Transient : a brief acoustic signal; a sound w a very short duration - E.g., click : typically less than 1 ms - Rule: the shorter the duration of the sound, the broader the amplitude spectrum

Transient Sounds

- Transient : a brief acoustic signal; a sound w/ a very short duration - E.g., click : typically less than 1 ms - Rule: the shorter the duration of the sound, the broader the amplitude spectrum

When sound media change, one of four things can occur :

- Transmission - Reflection - Absorption - Diffraction

Frequency tuning curves

- Tuning curves (getting the neuron to fire) for different auditory neurons w different CFs - Asymmetry of BM tuning curves is preserved

Duplex Theory of Localization

- Two cues for determining (horizontal) location: • ILDs at high frequencies • ITDs at low frequencies -- The theory dictates that we would rely upon ITDs at low frequencies because ILDs are not available

Primary structures of middle ear

- Tympanic membrane - Ossicles • Malleus, incus, stapes - Eustachian tube - Middle ear muscles • Tensor tympani muscle • Stapedius muscle

Organization of cochlear nerve bundle

- Unmyelinated between organ of corti & habenula perforata - Become a twisted bundle in the modiolus (spiral ganglion) • Nerve fibers innervating the hair cells at apex are at the center • Nerve fibers innervating the hair cells at the base are on the outside -Therefore, tonotopic organization is preserved in the cochlear nerve - Structural organization of frequency

Loudness

- Variations in sound level usually result in a change in perception of loudness - Loudness ranges from barely perceptible to uncomfortably loud - Loudness can be quantified in a number of ways

otoacoustic emissions

- spontaneous or evoked sound waves produced within the ear by the cochlea and escape from the ear - sounds emitted by the cochlea of the inner ear that show sex differences

An equal loudness contour displays sound intensity levels that result in the perception of equal loudness across the range of all frequencies audible to the human ear, with reference to a 2000 Hz tone at some loudness level.

False

Because ITDs and ILDs do not exist in the vertical plane, humans are unable to localize in the vertical direction.

False

Every individual neuron in the auditory nerve is able to encode the entire dynamic range of intensity that a person can hear.

False

For humans with normal hearing, our absolute thresholds (in dB SPL) are the same across all frequencies between 20-20,000 Hz.

False

If two sounds of 50 dB IL are played simultaneously, the resultant summed intensity is 100 dB IL.

False

Sounds that are consider maskers can only be noise, not tones.

False

The central auditory nervous system consists exclusively of afferent (ascending) projections.

False

The speed of sound is not affected by density or stiffness of its traveling medium.

False

True or false. A low-frequency sound is more likely to reflect off of a small interfering object than a high-frequency sound.

False

True or false. Any frequency of noise can mask out a signal, even if it falls outside of the critical bandwidth

False

True or false. Humans demonstrate equivalent performance in forward masking as in backward masking.

False

True or false. Information conveyed from the auditory nerve remains on the same (ipsilateral) side all the way up through the auditory cortex.

False

True or false. Standing waves are only generated at one frequency for a tube of a particular length.

False

True or false. The minimum audibility curve is the same regardless of what transducer (headphone, soundfield, etc.) is used.

False

The upward spread of masking is a phenomenon in which:

a tone is more susceptible to a masker with a lower frequency (below the signal frequency) than a higher frequency (above the signal frequency), especially at high intensity levels.

The smallest increment of change needed in order to determine a just noticeable difference between two otherwise identical stimuli is referred to as

a. The differential threshold.

The amplification of the traveling wave that occurs as a result of the electromotility of the outer hair cells is activated the MOST

at the CF, the peak of the traveling wave.

complex aperiodic sounds : continuous spectrum

Has a continuous spectrum - i.e., an INFINITE # of frequencies

bony labyrinth spiral ganglion

a collection of neurons in the modiolus of the cochlea that receives input from hair cells and sends output to the cochlear nuclei in the medulla via the auditory nerve

spiral ganglion

a collection of neurons in the modiolus of the cochlea that receives input from hair cells and sends output to the cochlear nuclei in the medulla via the auditory nerve

What is a technique used in psychophysical testing to avoid the confounding factors of bias?

c. Utilizing a forced-choice paradigm with two or more intervals

Masking w Noise/Critical Band - Noise terminology : narrowband noise

limited range of frequency components (used to map out PTCs)

Absolute threshold

lowest level of stimulation that is detectable some pre-specified proportion of the time

The ossicle attached to, and immediately medial to, the tympanic membrane is referred to as the ___________________.

malleus

What two properties must an object have to become a sound source?

mass & elasticity

electrocochleography

process of recording the electrical activity in the cochlea

inner ear function

hearing and equilibrium

outer hair cells

neurons in the organ of Corti; serve to amplify & sharpen the responses of inner hair cells

formulas : inverse square law

I = P/4pir^2 20 (log1/2)

saturation of a neuron

the state in which a neuron predominantly outputs values close to the asymptotic ends of the bounded activation function

resting potential

the state of the neuron when not firing a neural impulse

Intro to psychophysics Psychoacoustics:

the study of the psychological response to acoustical stimulation • The study of the perception of sound

compound action potential

the sum of the signals transmitted by several neurons

basilar membrane vibration

transduction of mechanical stimuli to neural signals

Masking w Noise/Critical Band - Noise terminology : white noise

All frequencies between specifies limits of bandwidth are present at the same average intensity of pressure

Complex sounds (periodic or aperiodic)

- Can be periodic or aperiodic • Periodic = repeats itself —> pure tone; sine wave • Ex: Complex sound : periodic : square wave; aperiodic : white noise

Psychoacoustics paradigms

- Auditory detection - Auditory discrimination - Auditory identification

IPDs in Lateralization

- 0°IPD - fused sound perceived at midline of head - Up to 180°IPD - fused sound located closer to ear that received tone first (leading in phase) - More than 180°IPD - fused sound located closer to ear receiving tone w lagging phase - 360°IPD - fused sound perceived at midline again

Other psychophysical methods Matching procedure

- 2 stimuli w different properties are presented (e.g. sounds of 2 different frequencies) - Listener asked to match equality along some stimulus attribute (ex. Loudness)

Central Auditory Nervous System - cochlear nucleus

- Auditory nerve fibers exit through the internal auditory canal within the temporal bone - Synapse at the ipsilateral cochlear nucleus - Located in the brainstem - Junction points between the medulla, pons, & cerebellum - cerebellopontine angle Dorsal: back Ventral: belly

Complex sounds

- Can have more than one frequency & starting phase • NOT sinusoidal (sine wave; simple sounds; pure tone)

Cochlear nerve fibers

- 2 types of fibers • Radial fibers: type I fibers • Outer spiral fibers: type II fibers - Type I fibers • Comprise 90-95% of the auditory nerve fibers • Exclusively innervate inner hair cells • Each neuron only innervates 1-2 IHCs • Each IHC may be innervated by 16-20 type I fibers - Many-to-one innervation • Thicker than type II fibers - Type II fibers • Compromise 5-15% of the auditory nerve fibers • Mostly innervate OHCs - "One-to-many" innervation - 1 fiber innervates about 10 hair cells • Basal end of cochlea — inert outermost row of outer hair cells • Toward apex — innervate middle & innermost rows of OHCs

Ossicles - stapes

- 3rd ossicle, attached medially to lenticular process of incus: "stirrup" - Head, neck, crura, footplate • Footplate sits against the oval window of the cochlea

Aperiodic Complex Sound

- A complex sound that does NOT repeat itself regularly over time • Does not include fundamental frequencies nor harmonics - Spectral energy is continuous, not distributed only at integer harmonics • Continuous : long duration - Has a continuous spectrum - i.e., an INFINITE # of frequencies

Cone of Confusion

- A cone of confusion exists for the location of every sound source - Sounds on surface of cone produce same ITD/ILDs - How do we compensate for this? - Possibly with head movement - However, localization is still possible even without head movement - Spectral cues • Head related transfer functions (HRTFs)

Tectorial membrane

- A gelatinous membrane immediately above Organ of Corti - Longest OHC stereocilia (kinociliia) embedded in underside of tectorial membrane - Assists w active amplification system of cochlea (to be discussed later) - Attached to a structure called the spiral limbus at the center of the cochlea (medial side) - Attaches to supporting cells on the lateral side

Scientific notation

- A system that allows us to quantify very large or very small #s more easily

Refractory period(s)

- Absolute refractory period: the amount of time during which a neuron cannot fire again (about 1 msec) - Relative refractory period: begins near end of polarization/hyperpolarization through restoration of resting state • Action potential can be initiated at this time, but greater depolarization is needed

Review: absolute sensitivity/loudness

- Absolute threshold • Auditory sensitivity • Minimum audibility curve • Threshold of pain/feeling • Dynamic range - dB hearing level scale - Loudness • Phon scale • Sone scale

Basis of MLDs

- Additional cues provided based on interaural time and level differences that aid in signal detection - MLDs for MoSπ decrease as frequency increases best at low frequencies - Consistent with claim that ITDs/IPDs are more effective at low frequencies

Afferent & efferent fibers

- Afferent fibers: carry information from peripheral sense organ to brain - Efferent fibers: bring information from higher neural centers to lower neural centers - Fibers of the auditory nerve (spiral ganglion) are largely afferent • (Efferent system will be discussed later when we talk about the olivocohlear bundle)

Speech sounds

- All complex - Vowel • Periodic complex sound - Fricative • /ʃ/ • Aperiodic continues complex speech sound - Stop consonant • Aperiodic transient complex speech sound - Simple sounds - pure tones, sine waves - Complex sounds • Periodic continuous • Aperiodic continuous • Aperiodic transient

White noise

- All frequencies between specifies limits of bandwidth are present at the same average intensity of pressure

Efferent system

- All neural pathways discussed up to this point have involved afferent projections - Efferent projections of central auditory system originate at • Superior olivary complex (olivocochlear bundle) auditory cortex • Play a role in affecting input form the periphery

Cochlear microphonic

- Alternating current (AC) potential from OHCs —> result of depolarization/hyperpolarization fluctuation - Potential oscillates at the same frequency as the incoming stimulus (sound) - CM amplitude proportional to displacement of BM - Only occurs during presentation of an acoustic stimulus - Because electrical potential measured matches stimulus so closely, it is related to the function of a microphone

Threshold shift from masking

- Amount by which threshold is increased by the presence of the masker: threshold shift - Example: voices detectable at 20 dB, but w background noise, not detectable until 50 dB • 30 dB threshold shift; 30 dB of masking

cochlear microphonic

- An alternating current (AC) whose frequency mimics that of the incoming stimulus -Acts like a "microphone" mimicking the incoming signal -Appears to be predominantly generated by the Outer Hair Cells

Review of exponents

- An exponent is a notation of how many times a # is applied by itself - 2 x 2 = 4 = 2 sq. - a • a • a • a = a to the power of 4 - A to the power of b (A is the base; b is the exponent) - A few basic exponent rules • X to the power of 0 = 1 • X to the power of 1 = X • X to the power of - y = 1/(X to the power of y) - 5 to the power of 0 = 1 - 23 to the power of 1 = 23 - 2 to the power of -2 = 1/4

All sound sources must have mass & elasticity

- Anything can be a sound source as long as they have these 2 - Mass • the amount of matter present in an object as characterized by weight & density (inertia) -- Requires a force to move -- Requires the perfect amount of mass to move - Elasticity • the ability of an object to return to its original state after a force has been exerted on it -- Ex: if you move a guitar string it's going to revert back to its original state - Inertia & elasticity counter each other • Move to a different state then come back to its original state : vibration - Vibration is the movement that results when a force is exerted on an object - Object is displayed by a certain force needed to overcome its inertia - Elasticity is the property that allows the object to restore itself to its resting state (equilibrium)

Low SRs

- Associated w higher thresholds (less sensitive to sound)

High SRs

- Associated w lower thresholds (more sensitive to sound)

Cochlear nucleus

- Auditory nerve fibers exit through the internal auditory canal within the temporal bone - Synapse at the ipsilateral cochlear nucleus - Located in the brainstem • Junction points between the medulla, pons, & cerebellum - cerebellopontine angle

Summary: The cochlear nerve: physiology & sound encoding

- Auditory nerve is able to encode frequency, intensity, & timing characteristics of incoming sound - Frequency encoded by • Preferential firing of neurons to a limited frequency region (especially CF) • Periodic firing (phase locking) for frequencies under 4-5 kHz - Intensity encoded by • Increase of firing rate above spontaneous rate of neurons • Number of neural fibers recruited (more neurons w different ranges of firing recruited over a large intensity range) • Neural synchrony also though to play a role - Timing/phase encoded by • Neural phase locking for frequencies under 4 - 5 kHz

Spontaneous firing rates (SR)

- Auditory neurons can be classified in 3 groups • Low firing rate (0 - 0.5 spikes/second) • Medium firing rate (0.5 - 18 spikes/second) • High firing rate (>18 spikes/second)

MGB —> auditory cortex

- Auditory tract fans out into auditory radiations to project to auditory cortex

Auditory Sensitivity - threshold : Minimum Audibility Curve

- Average thresholds in normally-hearing adults plotted as a function of frequency - Humans are sensitive to sounds between 20-20,000 Hz - More sensitive in the mid frequencies, especially 1 - 4 kHz - Most speech cues occur between 500-4000 Hz - Threshold of discomfort: about 100 dB SPL - Threshold of pain: about 125-140 dB SPL

Minimum audibility curve

- Average thresholds in normally-hearing adults plotted as a function of frequency - Humans are sensitive to sounds between 20-20,000 Hz - More sensitive in the mid frequencies, especially 1 - 4 kHz - Most speech cues occur between 500-4000 Hz - Threshold of discomfort: about 100 dB SPL - Threshold of pain: about 125-140 dB SPL

Saltatory conduction

- Axons of many neurons are wrapped in sheath of myelin - insulates cell membrane & prevents it from "leaking" - Allows action potential to propagate down axon at a much faster rate - Nodes of ranvier - gaps between myelination • Action potential "jumps" between nodes

Basilar membrane

- BM will experience maximum displacement at different places depending on frequency of incoming vibrations - Higher frequencies will maximally displace BM closer to the base (higher stiffness) - Lower frequencies will maximally displace BM closer to the apex (higher mass) - Traveling wave • displacement /movement of basilar membrane - TW starts at the base & grows until it reaches a maximum displacement corresponding to its resonant frequency

Masking w Noise/Critical Band - critical band theory : Patterson notched noise experiment

- Band-reject noise used instead of band-pass - Noise outside of auditory filter: no masking (detection unaffected) - Notched-noise method provides way to estimate shape & width of critical band - The wider the spectral notch (w no noise) the lower the threshold of the signal - Threshold determined by total amount of power coming through filter

Notched noise method (Patterson, 1976)

- Band-reject noise used instead of band-pass • Noise outside of auditory filter: no masking (detection unaffected) • Notched-noise method provides way to estimate shape & width of critical band • The wider the spectral notch (w no noise) the lower the threshold of the signal • Threshold determined by total amount of power coming through filter

Noise Terminology

- Bandwith: quantified range of frequencies in a sound (highest frequency - lowest frequency) - Total power: sum of amplitudes of all sinusoids in spectrum of noise - Signal to noise ratio (SNR): level of noise (in dB) subtracted from level of signal (in dB) • Ex: 60 dB tone, 70 dB noise = -10 dB SNR

Frequency encoding by place

- Basilar membrane is tonotopically organized: hair cells will be maximally stimulated depending on location along basilar membrane - Auditory neurons innervate only 1-2 IHCs —> tonotopic organization of BM is preserved - Each neuron will respond best to one frequency —> tuned to 1 frequency - This is referred to as place coding mechanism of frequency - Neurons will respond (increase firing above SR) to tones of many different frequencies - Does not discharge equally to all frequencies: is tuned to respond best to one frequency (characteristic frequency) - The characteristic frequency of a neuron will require the LEAST amount of sound (lowest threshold) to result in neural firing - Other frequencies above/below will require greater sound intensity to elicit an equivalent response - Each auditory neuron has a tuning curve - Tip = frequency at which neuron is most easily stimulated - Lowest intensity level of sound needed to raise neuron firing rate above spontaneous rate - Tip of tuning curve = neuron's characteristic frequency

Effects of binaural input

- Binaural summation • Thresholds approximately 3 dB lower w binaural input - Improved DLI/DLF • Lower thresholds for discrimination of intensity and frequency - Binaural fusion • One sound heard instead of 2 - Localization/lateralization - Binaural masking effects

Ossicles

- Bones suspended in middle ear cavity (by ligaments) connecting TM & inner ear • Malleus • Incus • Stapes

Inner ear structures

- Bony labyrinth: a series of intricate cavities of petrous portion of temporal bone housing the inner ear • Filled w perilymph • High in sodium (Na+), low in potassium (K+) - Membranous labyrinth: located inside bony labyrinth • Filled w endolymph • High in potassium (K+), low in sodium (Na+) • Inner ear organs are houses within the membranous labyrinth

Frequency encoding

- Both place & temporal coding mechanisms appear to contribute to frequency encoding in general - Phase-locking appears to be more limited

Cerebral Cortex

- Brain tissue - Gyrus/gyri - Sulcus/sulci - Longitudinal fissure - Central sulcus - Lateral sulcus

Horizontal Localization Accuracy

- Broadband noise contains wide range of frequencies - Accuracy of localization very high

Noise Terminology continued

- Broadband/wideband noise: noise containing a large range of frequency components - Narrowband noise: limited range of frequency components (used to map out PTCs)

Hair cell components

- Cell body w cuticular plate on top - Stereocilia • sensory receptors embedded in cuticular plate on top of cell - Kinocilium • longest stereocilium - Contain pores in top that open with excitation - Stereocilia connected to each other by filaments known as tip links & cross links

Telencephalon

- Cerebral cortex - Corpus callous - Basal ganglia

Clinical application

- Certain tumors that grown on the cochleovestibular nerve (acoustic neuromas) will typically cause a high frequency hearing loss because they are commonly located on the OUTSIDE of the nerve

Changes in loudness

- Changes in loudness are highly correlated w changes in level - However, loudness is also affected by changes in frequency, duration, bandwidth - Intensity is NOT the only characteristic of sound that can affect loudness perception

Summary: psychophysical methods

- Classical methods • Method of limits (adaptive) • Method of adjustment (adaptive) • Method of constant stimuli (not adaptive) - Other methods/techniques • N-interval forced choice vs. yes/no forced choice • Adaptive/staircase method w n-interval forced choice • Magnitude estimation • Matching procedures adaptive = changes according to the person's performance

Main structures of inner ear

- Cochlea • Primary structure for hearing - Otoliths (vestibule) • Organs for balance: linear acceleration - Semicircular canals • Organs for balance: rotational movement

Cochlear frequency encoding

- Cochlea provides 2 types of cues for frequency of vibrations: 1. Place: BM displaced most near CF, therefore hair cells at/near CF are depolarized 2. Timing: stereocilia shear at the same rate of vibration of stapes footplate —> rate of vibration is therefore preserved

CANS nuclei roadmap

- Cochlear nucleus —> brainstem - Trapezoid body —> brainstem - Superior olivary complex —> brainstem - Nuclei of lateral lemniscus —> brainstem - Inferior colliculus —> brainstem - Medial geniculate body —> thalamus - Auditory cortex —> cerebral cortex

Compound action potential (CAP)

- Comes from the neurons of the spiral ganglion (not actually the cochlea) firing synchronously (at the same time) - Occurs at a set latency after the presentation of the stimulus • Latency = time elapsed - Response latency —> 1.0 to 2.0 ms after stimulus presentation - Typically a large (-) deflection (N1) followed by a (+) deflection (P1) - The better the neural synchrony (more neurons firing at once), the larger the response

Masking Level Differences

- Comparison of differences in masking are made between baseline monotic condition (MmSm) and diotic/dichotic conditions - Change in amount of masking (i.e., improvement in signal detection in presence of masker compared to monotic condition) is referred to as masking level difference (MLD) • Binaural masking level difference • Expressed in decibels

Tympanic membrane - quadrants

- Conceptually divided into 4 quadrants : superior/inferior, anterior/posterior - Anterior/posterior will look different depending on side

Structures of outer ear

- Concha: bowl/cave in center portion of pinna • Cymbal concha (superior portion) • Cavum concha (inferior portion) • Separated by crus of helix - Concha diameter: approximately 1 to 2 cm. - Leads to an opening w a diameter of about 5 to 7 mm: external auditory meatus - External auditory canal —> 2 to 3 cm. in length - Diameter of canal is larger at opening of canal • Narrows to a point called the isthmus • Open backs up past the isthmus leading to tympanic membrane - Not entirely straight: more S - shaped • More horizontal in children under 3 - Canal can be innervated by several cranial nerves - CN V - trigeminal nerve - CN VII - facial nerve - CN IX - glossopharyngeal nerve - CN X - vagus nerve • Cough reflex - "Arnold's reflex" - Outer (lateral) 1/3 of ear canal has a foundation of cartilage - Lined w hairs & glands: • Ceruminous glands - wax secreting • Subaceous glands - oil secreting - Inner (medial) 2/3 has an osseous (bony) foundation • No glands

Tympanic membrane - landmarks

- Cone of light: in anterior inferior quadrant - Umbo: point of maximum concavity • Center of TM • Where manubrium of malleus (first ossicle) can be visualized

sound propagation : constructive & destructive interference

- Constructive interference : overlap of two points of rarefaction or two points of condensation, resulting in a greater rarefaction/condensation (net addition of the waveforms) - Destructive interference : overlap of rarefaction & condensation resulting in a lesser rarefaction/condensation (net subtraction or cancellation of waveforms)

Anatomical planes

- Coronal • Vertical plane that divides into dorsal/ventral (or anterior/posterior) sections - Transverse • Horizontal plane that divides body into superior/inferior sections - Sagittal • Vertical plane that divides body into left/right sections (perpendicular to coronal & transverse planes) -- midsagittal • Sagittal section directly in middle

Propagation of action potential

- Current flow in cell due to ion transport in & out of cell - Current flow propagates to next section of axon & depolarizes next section - Action potential is propagated down the axon until it reaches the synaptic terminal

Outer hair cell

- Cylinder-shaped, 10 um in diameter - 10 to 90 um in length - 3 or more rows stereo cilia on each cell, graded in length (shortest is at the medial end) - Between 50 - 150 stereocilia per cell - Sterocilia form a "V" or "W" shape

Anatomy of a neuron

- Dendrites : fibers that receive messages from other neurons - Cell body (with nucleus) integrates incoming signals from dendrites - Axons : fibers that carry outgoing signals to other neurons or organs. There are gaps between - Synapse: region where the neuron meets other neuron or target cell - Signals are sent via Neurotransmitters

Hair cell depolarization

- Depolarization only happens once per cycle - Depolarization of hair cell results in the release of neurotransmitter - Diffuses through bottom of hair cell onto nerve fiver of vestibulocochlear nerve (postsynaptic cleft) - Leads to firing of vestibulocochlear nerve

Resting potential: hair cell potential

- Hair cells have resting potential -70 mV - Difference in potential across top of hair cells between inside & outside of hair cell = +80 mV - (-70 mV) = 150 mV

Masking w Noise/Critical Band - critical band theory : Equivalent rectangular bandwidth (ERB)

- Derived critical bandwidth: equivalent rectangular bandwidth (ERB) • ERBn = 24.7 (4.37F + 1) - F is center frequency, in kHz - ERBs of auditory filters derived are usually between 11% & 17% of center frequency • Ex: ERB 1000 = 24.7 (4.37(1) + 1) = 132.6 Hz • About 13% of 1000 Hz - The area of the rectangle is the same as the area under the curved auditory filter, but because it is a rectangle, it is easy to define the lower & upper bandwidth frequencies, which gives us the reason for the name equivalent rectangular bandwidth

Equivalent rectangular bandwidth (ERB)

- Derived critical bandwidth: equivalent rectangular bandwidth • (ERB) ERBn = 24.7 (4.37F + 1) - F is center frequency, in kHz - ERBs of auditory filters derived are usually between 11% & 17% of center frequency • Ex: ERB 1000 = 24.7 (4.37(1) + 1) = 132.6 Hz • About 13% of 1000 Hz

MLDs Dichotic

- Dichotic: MπSm • Signal presented to one ear • Masker presented to both ears, out of phase Improvement (MLD) of 6 dB - Dichotic: MoSm • Signal presented to one ear • Masker presented to both ears, in phase • Improvement (MLD) of 9 dB - Dichotic: MπSo • Signal presented to both ears, in phase • Masker presented to both ears, out of phase • Improvement (MLD) of 13 dB - Dichotic: MoSπ • Signal presented to both ears, out of phase • Masker presented to both ears, in phase • Improvement (MLD) of 15 dB

Cerebral cortex

- Different sulci divide cerebral cortex into 4 lobes: frontal, parietal, temporal, & occipital - Longitudinal fissure divides cortex into 2 hemispheres (left & right) - Corpus callous: large bundle of neural fibers connecting the 2 hemispheres - Central sulcus runs in a rostral/caudal direction - Creates the anterior/posterior boundary between frontal & parietal lobe - Lateral sulcus (also called Sylvian fissure) divides temporal lobe from frontal/parietal lobes

Psychophysical Methods - threshold : Differential threshold/discrimination

- Differential threshold: smallest magnitude of difference that allows a person to differentiate between two nearly identical stimuli • Also referred to as discrimination

Binaural masking conditions

- Diotic • MoSo - Monotic • MmSm - Dichotic • MoSπ • MoSm • MπSo • MπSm

MLDs Diotic

- Diotic: MoSo - Signal and masker presented to both ears, in phase with each other - No masking level difference observed

Summating potential

- Direct current (DC) electrical response recorded from cochlea - Baseline shift recorded only whenever stimulus is present - Can be either (+) or (-) - Could come from either outer/inner hair cells (or other places)

Summary --> The inner ear: cochlear electrophysiology

- Direction of stereocilia shearing with movement of basilar membrane - Oval window outward —> rarefaction —> BM up —> stereocilia AWAY —> tip links OPEN —> depolarization - Oval window inward —> condensation —> BM down —> stereocilia TOWARD modiolus —> tip links CLOSE —> hyperpolarization - Potassium (K+) influx causes depolarization - Decreases difference in potential charge between inside of hair cell & endolymph - Remember, there is a BIG difference between the two by default (+80 mV endolymph, -70 mV hair cell) - Depolarization triggers release of neurotransmitter onto surface of neurons of auditory nerve - This will result in FIRING of auditory nerve - There are multiple POTENTIALS that can be measured in the cochlea at rest or when there is a sound coming in - Resting potentials —> default charges within the cochlea - CM, SP, & CAP —> can be measured from the cochlea with sound - CM & CAP —> alternating current - SP —> direct current

Properties of a sine wave

- Displacement : the amount of movement away from state of equilibrium at any given point in time - Maximum & minimum displacement are also referred to as the peak amplitude, defined as -A to equilibrium, or equilibrium to +A (always a positive #) - Peak-to-peak amplitude : twice the peak amplitude, or +A to -A (always a positive #); distance between center & peak amplitude - Period : the amount of time needed for the oscillation (revolution) to complete one cycle • Typically measured in seconds or milliseconds • Cycle : go up/down then back to center - Frequency : the rate at which the object vibrates (or oscillates/cycles); in other words, the # of vibrations per specific unit of time • Typically measured in cycles per second, or Hertz (Hz) - F = 1/period; period = 1/frequency

Characteristics of traveling wave

- Displacement of membrane is larger for higher amplitude sounds - Basilar membrane moves up & down in synchrony w the vibrating stimulus (i.e, will move at a rate of 1000 Hz w a 1000 Hz tone) - TW is more uniform/less dispersive ("sharper") as basal end - TW is more dispersive & less uniform at apical end (more "rounded") - Because of the way the BM is laid out, low-frequency sounds can stimulate the basal & apical ends of the cochlea - High-frequency sounds can only stimulate basal end of cochlea

Basilar membrane gradient

- Displacement of scala media causes movement of basilar membrane - Mass-stiffness gradient • BM is stiffer/narrower at base, wider/floppier at apex - In other words, characteristic impedance of BM changes along its length!

Examples of common sources of vibration that result in sound

- Drum head - Guitar string - Diaphragm of a speaker - Human vocal folds

Forced-choice paradigm

- Each trial contains at least two period of time called intervals • Ex: two-interval alternative forced choice (2IFC) • Only one interval contains correct response - Participant chooses one interval per trial

Cerumen

- Earwax/cerumen formed by the secretions of these glands combined w dead skin - Cerumen is NORMAL - Protection against foreign bodies/insects

Binaural masking

- Effectiveness of a masker can be different depending on the phase relationship of signal/masker presented to both ears - Monotic • Stimuli presented to only one ear - Idiotic • Identical stimuli presented to both ears - Dichotic • Different stimuli presented to two ears

Other cochlear potentials

- Electrical charges that can be measured in the cochlea w respect to a reference point - Can be direct current (DC) or alternating current (AC) - AC: potential changes that vary over time • Fluctuate from (+) to (-), etc.

Middle ear structures

- Encased within temporal bone of skull - Air-filled cavity divided into 2 sections • Tympanic cavity/tympanum • Epitympanic recess - Bounded laterally by the tympanic membrane - Bounded medially by the promontory • A prominence next to the round window of the cochlea (part of the inner ear)

Organ of corti

- End organ of auditory inner ear - Inside scala media, seated on the basilar membrane - Hair cells: sensory receptor cells inside • Inner hair cells (IHCs) • Outer hair cells (OHCs) - Tectorial membrane - Supporting cells/structures

Phon scale - equal loudness contour

- Equal loudness contour: curve demonstrating sound level at each frequency that results in an equal loudness level in reference to particular 1000 Hz tone - All values along each equal loudness contour have the same number of phons - Note: curves do NOT show how different phon levels relate to each other

Psychophysical methods: method of limits

- Ex: finding threshold of sound intensity - Intensity of stimulus is changed until it is barely detectable to listener - Can be ascending (increasing in intensity) or descending (decreasing in intensity) - Reversal: when the stimulus changes from ascending to descending depending not the listener's response - Threshold is averaged over reversals Consistent step size of stimulus property is used in method of limits (e.g., 5 dB) - Method of limits is considered an adaptive procedure: the listener's response will dictate the next stimulus level - Clinical audiometry is based on the method of limits

Critical band theory: experiments

- Experiments initially conducted by fletcher (1940) - Detection of a tone in noise - Bandwidth of noise slowly increased

More exponent rules multiplying & dividing

- Exponents can be multiplied & divided but • only if the bases are equal 10^1 x 10^6 • 82^5/82^7

Loudness adaptation

- Exposure to a long-duration stimulus results in loudness adaptation - Perceived loudness of sound decreases • Seconds or longer

HRTF Cues

- External parts of head/body/pinna act as small sound shadows - Also delay sound in reaching outer ears - Interaction between sound and body is different depending upon location of sound - Head & torso provide spectral - HRTF alteration of sound source - Especially at high frequencies

Anatomical course of auditory nerve fibers

- Fibers exit cochlea radially and become the auditory nerve trunk - course through opening in temporal bone - internal auditory canal • One branch of the vestibulocochlear nerve, CNVIII- Course toward brainstem

The cochlear nerve: physiology & sound encoding Review:

- Firing of auditory neurons begin w hair cell depolarization (mostly IHC) - Inner hair cell releases neurotransmitters that create a graded potential diffusing though the cell (PSP) - Depolarization to threshold —> action potentials (neural spikes, neural firings) - Neurons will encode incoming sound according to characteristics related to frequency, amplitude, timing

Firing rate

- Firing rate/discharge rate/spike rate - number of times neuron fires per second - Absolute refractory period is 1 msec - Theoretical maximum firing rate is 1000 Hz in a neuron (why?)

Masking w Noise/Critical Band - critical band theory : Fletcher bandpass experiment

- Fletcher measured the threshold of a sinusoidal signal as a function of the bandwidth of a noise masker - The noise was always centered at the signal frequency and the noise power density was held constant - The total noise power increased w bandwidth.

Modern psychophysical methods

- Forced-choice task paradigm used in conjunction w advanced adaptive procedure - Participant chooses one interval per trial - Stimulus property adapted according to algorithm for perforce correct • Ex: 2 down, 1 up - Step size may be changed depending on performance to make things more efficient - Results in one estimated threshold along psychometric function - Much quicker than using method of constant stimuli

Temporal masking

- Forward & backward masking have the greatest effects when the interval between signal & masker is short • Within 200 msec for forward masking • Within 50 msec for backward masking - The longer the interval (delta t), the lower the signal threshold; in other words, the less the effect of the masker - Effects of temporal masking decay very quickly after reaching the intervals mentioned above

Basic Physical properties of sound

- Frequency - Amplitude (intensity/sound pressure) - Time (temporal characteristics)

Critical bandwidth increases w:

- Frequency (but after scaling), frequency selectivity is equivalent - Intensity level - Cochlear hearing loss - The narrower the bandwidth, the better the frequency selectivity • Better discrimination

Passive vs. active mechanics

- Frequency tuning of BM described by von Bekesy is too broad to explain frequency tuning in humans (remember, he studied cadavers) - Frequency tuning according to the basilar membrane & tonotopic organization can be explained by passive cochlear mechanics - Active cochlear mechanics were discovered in 1950s-1970s - Outer hair cell motility contributes to active cochlear mechanics, which increases sharpness of frequency tuning at low/moderate intensities (not at high intensities) • Better frequency selectivity • Considered a "nonlinear" mechanism

Superior olivary complex

- From CN, fibers project both ipsilaterally & contralaterally to superior olivary complex - 2/3 fibers decussate: cross over through trapezoid body - About 1/3 gibers project ipsilaterally - First place in the auditory nervous system that receives information from the other side - Group of nuclei clustered in the pons - First place where binaural (both sides of auditory system) information is represented - Major functions include: • Localization • Efferent regulation of auditory system • Stapedial/tensor tympani acoustic reflex

In a partially enclosed space (i.e., tube w one end open & one end closed):

- Fundamental frequency occurs when frequency has a wavelength that is 4 times the length of the space -- f0 = c/4L - Thus, antinodes are only produced at ODD multiples of the fundamental frequency (3 f0, 5 f0, 7 f0, etc.)

Complex periodic sound - octave

- Harmonic series can be divided into octaves boundaries marked by harmonics that are a factor of 2^n of the fundamental frequency • There is not sound present in every single harmonic : still a periodic sound (square wave) - 1st octave = f0 * 2^1 - 2nd octave = f0 * 2^2 - 3rd octave = f0 * 2^3 - Nth octave = f0 * 2^n

dB SPL to dB HL

- Hearing instruments calibrated to set these thresholds as references - Referred to as dB hearing level, or dB HL - Average thresholds = 0 dB HL

Sensitivity to duration

- Hearing sensitivity improves as sound duration increases • Lower threshold - Improved sensitivity plateaus at durations of 250-500 msec. Longer - Below this range, level of sound must be increased for equivalent detection - We refer to this ability of the auditory system to assimilate sound energy over time as temporal integration - The normal auditory system requires about 300 msec to complete temporal integration

Cochlea - helicotrema

- Helicotrema: narrow duct @ apex of cochlea where scala vestibuli & scala tympani meet —> the one place where they are continuous - Otherwise the membranes are intact & separate the chambers from each other - Fluid flow begins w compression of the oval window via the stapes - Pressure wave progresses through scala vestibuli, passes into the scala tympani through helicotrema - Displaces the round window

Landmarks of pinna

- Helix: outside ridge, superior to EAM • Crus of helix: ridge continued from anterior/superior portion of helix -- Divides concha into 2 parts - Antihelix: ridge inside helix, runs approximately parallel • Splints into 2 segments : crura of anti helix - Scaphoid fossa: between helix/antihelix (anterior to helix, posterior to antihelix) - Triangular fossa: depression formed by crura of antihelix, medial to scaphoid fossa - Tragus: small flap of cartilage on anterior wall of EAM • Connected from anterior portion of helix - Antitragus: opposite of tragus, connected from posterior portion of anti helix • Tragus/antitragus separated by notch: intertragal incisure - Lobule - "earlobe," where the posterior course of the helix terminates

Temporal encoding

- Histograms are plotted to observe the behavior of neural firings over time - Postimulus time (PST) histograms: total number of discharges/responses over a period of time after onset of stimulus - Neural adaptation: decrease in number of neural firings over duration of stimulus - Interspike interval (ISI) histograms: visualization of time interval between successive pairs of neural discharges - Number of discharges for each interspike interval - Regular peaks seen in ISI histograms are indicative of phase locking - Note that this pattern becomes weaker at higher frequencies

Practice - Phon scale

- How many phons loud is a 1000 Hz tone at 65 dB SPL? • 65 phons - How many phons loud is a 2000 Hz tone that is judged to be as loud as a 1000 Hz tone at 65 dB SPL? • 65 phons

Absolute vs. differential sensitivity

- How sensitive are we to changes in properties of acoustic signals? - Difference threshold = just noticeable difference (jnd) or difference limen (DL)

Lateralization Effects

- Identical phase/level • Fusion at midline - Increased intensity on the right • Fusion toward the right - interaural phase difference w lead on the right • Fusion will depend on phase difference

Psychophysical Methods - Classical Methods: Method of constant stimuli

- If one wants to know how signal intensity affects the subject's response rate, the method of constant stimuli can be used. - A (constant) number of stimuli per intensity will be presented, & the subject's response (or failure to respond) will be recorded

Standing waves

- In enclosed or partially enclosed spaces, standing waves can be produced - Standing wave -- when a sound wave is continually reflected off of a surface in such a way that when the two encounter each other, they produce a pattern of minimum & maximum displacements that does not appear to propagate through space - In other words, standing waves occur when there is perfect constructive interference of an incident wave & its reflection in an enclosed space • Tube closed at both ends • Tube closed at one end, open at the other • Tube open at both ends - These spaces are considered to be enough enclosed that standing waves can occur - If sound is flowing through a tube, it is reflected regardless of whether the end is open or closed - Frequency is dependent on size of tube

Localization accuracy by frequency

- In mid-frequency range (around 2000 Hz), neither cue is as strong - Localization more difficult

Intensity discrimination

- In this figure -- a constant ∆I in dB (flat horizontal line) is equivalent to a constant ∆I/I (in absolute pressure/intensity) - Weber's Law applies best to wide-band noise - Threshold for ∆I decreases slightly for pure tones as level increases - Wideband noise almost follows Weber's law ("near miss"); better than for tones

Intensity encoding

- Increases in firing rate - Higher intensity sounds activity greater numbers of neurons

Recap - Basic Neurophysiology

- Influx of Na+ causes depolarization - When depolarization reaches threshold, action potential is initiated - Action potential: all or none - Caused by influx of Na+ - Cell is depolarized up to a peak - As Na+ is coming in, K+ leaving - After peak of AP: - Na+ stops entering cell - K+ continues to leave cell - Repolarization to original resting potential - Hyperpolarization - as K+ continues to leave cell, there is an overshoot past resting potential -Absolute/relative refractory period: period of time during which cell cannot fire again, or needs a significantly greater depolarization to fire again

Nervous system

- Information processing system that regulates all of the physiological functions of an organism - Manipulates information about external/internal environments - Representations of external world converted into electrical signals that are then processed by the organism - Central nervous system (CNS) Brain, spinal cord Peripheral nervous system (PNS) All nerves outside of CNS (including cranial & spinal nerves)

Cochlear function overview

- Information regarding incoming sound transmitted to nervous system through preferential vibration of basilar membrane - Sensory cells in the Organ of Corti corresponding to vibrating location of BM undergo chemical reaction - Vibrations are transformed into a neural impulse in the spiral ganglion

Hair cells: Innervated by nerve fibers

- Innervations from auditory nerve fibers of CN VIII located at the base of hair cells - Exit through pores in spiral lamina called habenulae perforata - Nerve fibers bundle to form spiral ganglion in the core of the modiolus - Becomes the cochlear branch of CNVIII (vestibulocochlear nerve)

Instantaneous vs. starting phase

- Instantaneous phase varies w time (t) - Starting phase refers especially to the phase at t = 0 ms. - Can vary from 0-360, or 2pi radians

Interaural Level Differences

- Intensity level of sound is greater at one ear than the other • Head sound shadow results in reduced sound level at ear opposite sound source - Dependent upon frequency - Larger ILDs exist at high frequencies - ILDs are a better cue for localization at high frequencies

Intensity vs. loudness

- Intensity/pressure —> a physical characteristic of sound - Loudness —> the perceptual correlate associated w changes in intensity/pressure of sound

Differential Sensitivity - Temporal discrimination

- Interactions between duration of sound & detectability/spectrum - Measured w gap detection-sensitivity to separation of sounds based on duration of gap preceding the presentation of the second sound - Threshold for ∆T increases as a function of temporal separation - the ability to determine that two sequential sensory stimuli are separated in time

Temporal discrimination

- Interactions between duration of sound and detectability/spectrum - Measured w gap detection- sensitivity to separation of sounds based on duration of gap preceding the presentation of the second sound - Threshold for ∆T increases as a function of temporal separation - Does not quite follow Weber's Law

Review of MLDs

- Interaural condition compared to MmSm MLD - MmSm, M0S0 : 0 dB - MπSm : 6 dB - M0Sm : 9 dB - MπS0 : 13 dB - M0Sπ : 15 dB

Sound fields & reverberations

- Inverse square law only applies to a free sound field (sound field free of obstructions) - In actuality, most sound environments have boundaries which create the opportunity for reflection/diffraction/absorption • Reflection/absorption are more likely to occurs when you hit a difference in impedance - Ex: a physical change (hitting a wall —> sound will bounce off) Reverberation time: The time needed for a sound to decrease by 60 dB

Standing wave : Open both ends

- It is also possible to get standing waves when the tube is open on one or both ends. - Mathematically, standing waves w both ends open have the same formulas for F0 • f0 = c / 2L

Psychophysical tuning curve (PTC)

- It is not realistic/possible to directly measure neural tuning curves in humans - However, we can assess tuning through psychophysical measures —> a behavioral correlate to the auditory neural tuning curve - We call this a psychophysical tuning curve - A PTC can be mapped out w a masking experiment - Stimulus = tone - Masker = narrowband noise (noise centered over a frequency band —> to get it as close to a pure tone as a noise can get!) - Signal: pure tone at a set frequency & sound pressure level - Masker: narrowband noise centered at different frequencies (500 Hz, 1000 Hz, 2000 Hz, etc.) - The level of the noise needed to just barely mask perception of the tone is plotted at each frequency

Fourier's theorem

- Jean-Baptiste Joseph Fourier - Any complex sound can be decomposed into a series of sinusoidal waves - In other words, all sounds, no matter how complex, can be broken down into basic simple sine waves - Complex sounds • simple sine waves (pure tones) form the building blocks of all complex sounds • Complex sounds are created by adding sine waves of different frequencies together

Localization defined

- Judgements of the direction and distance of a sound source occurring in space - Exists in 3 spatial dimensions: • Horizontal plane (azimuth) • Vertical plane • Distance (range)

tympanic membrane - pars tense

- Largest portion of TM (2/3); contains many fibers, more taut - Fibers give it more rigidity to vibrate

Lateral lemniscus

- Lateral lemniscus: tracts of fibers originating from cochlear nucleus • Join w fibers projecting from superior olivary complex to continue to next nucleus - Several nuclei among fiber tracts: nuclei of the lateral lemniscus (NLL) - Some fibers from SOC project to ipsilateral NLL, others contralateral NLL - Some fibers skip NLL entirely

Central auditory nervous system - nuclei of lateral lemniscus

- Lateral lemniscus: tracts of fibers originating from cochlear nucleus Join w fibers projecting from superior olivary complex to continue to next nucleus - Several nuclei among fiber tracts: nuclei of the lateral lemniscus (NLL) - Some fibers from SOC project to ipsilateral NLL, others contralateral NLL - Some fibers skip NLL entirely

Other psychophysical methods Magnitude estimation

- Listener is asked to judge magnitude of subjective attribute (loudness, pitch, timbre, etc.) - Participant assigns a number to the magnitude of the stimulus - Scale relating perceived magnitude to physical stimulus is created - This can occur w or w/out a reference (e.g., "this loudness level is a 5")

Other psychophysical methods Fractionation

- Listener is asked to make the stimulus some fraction of its original quality - E.g. "make this half as loud"

Discrimination of Location

- Listeners blindfolded are asked to discriminate between location of two small speakers - Minimal audible angle smallest angular separation between two sounds detectable by listener

Complex pitch perception

- Listeners can perceive a pitch for complex sounds - even if there are not spectral components at the perceived pitch! - Missing fundamental pitch • Perception of the pitch at the fundamental frequency even if not present in a complex sound • Ex. people will perceive a sound at 100 Hz for a stimulus that just has 700, 800, 900, and 1000 Hz

Inferior Colliculus

- Located in the midbrain - Receives stimulation from both SOCs - Some fibers from cochlear nucleus travel directly to the inferior colliculus - Connected by fibers that allow for direct crossover & communication between them • Last place in the CANS where crossing over occurs • Fibers exiting IC project ipsilaterally ONLY

Central Auditory Nervous System - inferior colliculus

- Located in the midbrain - Receives stimulation from both SOCs - Some fibers from cochlear nucleus travel directly to the inferior colliculus - Connected by fibers that allow for direct crossover & communication between them • Last place in the CANS where crossing over occurs • Fibers exiting IC project ipsilaterally ONLY

Central Auditory Nervous System - Medial geniculate body

- Located in the thalamus, in the diencephalon (right below the cerebral cortex) - Receives ipsilateral projections from the inferior colliculi - Some fibers from nuclei of lateral lemniscus bypass inferior colliculi & project directly to here - Auditory tract fans out into auditory radiations to project to auditory cortex

Medial geniculate body

- Located in the thalamus, in the diencephalon (right below the cerebral cortex) - Receives ipsilateral projections from the inferior colliculi - Some fibers from nuclei of lateral lemniscus bypass inferior colliculi & project directly to here - Auditory tract fans out into auditory radiations to project to auditory cortex

Laws of logarithms : 1st law of logarithms

- Log (a x b) = log a + log b - Example: • Log (10x2) = log10 + log2 • 1 + log2 • 1 + .301 • 1.301

Law of logarithms : 2nd law of logarithms

- Log (a/b) = log a - log b - Example: • solve for x & display answer in scientific notation • 5 = log(10/x) • 5 = log10 - log x • Log x = log 10 - 5 • Log x = -4 • X = 10^-4 • X = 1.0 x 10^-4

Some general things to remember : logs

- Log a A = 1 - Log a 1 = 0 - Log a A^x = X

Law of logarithms : 3rd law of logarithms

- Log a^b = b x log a - Example: • log(10x/y)^3 = 3log(10x/y) • log(a/b)^2 • 2xlog(a/b) or 2x(loga - logb)

Common used logs : log(10)x

- Logarithms are frequently displayed in log base 10 - Ex. Log(10)X is typically just displayed as log X - You can use the log function on your scientific calculator; the default is log base 10 - Log 1 = 0 - Log 10 = 1 - Log 100 = 2 - Log .001 = -3

Practice exercises Solve for x w/out using a calculator : Logx27 = 3 X = log(6)36

- Logx27 = 3 • x^3= 27 • (x^3)^1/3 = (27)^1/3 • x^1 = 3 • X = 3 - X = log(6)36 • 6^x = 36 • X = 2

Phon scale

- Loudness of sounds are compared to a reference tone of 1000 Hz at a particular level (e.g. 40 dB SPL) - A tone of 1000 Hz at 40 dB SPL has a loudness level of 40 phons - Any other sound w an equivalent loudness level will also have a loudness level of 40 phons - what different sound pressure levels are needed across frequencies for the perception of equal loudness.

Four types of filters

- Low-pass - High-pass - Band-pass - Band-reject

Minimal Audible Angle

- MAA is very high (poor discrimination) at mid frequencies —> therefore, discrimination of location is also poor at mid frequencies - Better at low/high frequencies - Notice that MAA is worse with increased azimuth (best near midline)

Localization in azimuth

- Major cues for horizontal localization: • Interaural time differences (ITDs) -- Interaural phase differences (IPDs) • Interaural level differences (ILDs) • Duplex theory of localization

Masking - signal & masker

- Masker vs. signals - Maskers create a threshold shift - Maskers will be most effective if they are close in frequency to the signal frequency Example Signal: 1000 Hz tone Which masker is best (most effective)? 1003 Hz 822 Hz 506 Hz 1600 Hz Closest one —> low —> high

Review: General Masking principles

- Masker vs. signals - Maskers create a threshold shift - Maskers will be most effective if they are close in frequency to the signal frequency - Psychophysical turning curves (PTCs) are reflective of frequency selectivity & are behavioral correlates of the neural tuning curves of the cochlear nerve & the basilar membrane

Masking - Threshold shift

- Maskers create a threshold shift - Amount by which threshold is increased by the presence of the masker: threshold shift - Example: voices detectable at 20 dB, but with background noise, not detectable until 50 dB • 30 dB threshold shift; 30 dB of masking

Upward spread of masking

- Maskers w frequencies lower than signal frequency are more effective at masking than makers w higher frequencies than signal - Referred to as upward spread of masking - Especially at high intensity levels

Review: masking

- Maskers w frequencies lower than signal frequency are more effective at masking than maskers w higher frequencies than signal - Referred to as upward spread of masking - The BEST frequency of masking is still close to the same frequency, especially for narrowband noise - Direct result of the asymmetric shape of the traveling wave created by the mass stiffness gradient of the basilar membrane

Masking

- Masking: when one sound interferes w the decidability of another sound - Threshold of ones sound (signal) is raised, or increased by presentation of another sound (masker) - Example: conversation at restaurant masked by background noise

Mass & String Example

- Mass : at rest - Mass : disturbance caused by force; inertia perpetuates motion - Mass : compressed as a result of elasticity - If there were no resistive forces, the vibrations would continue forever - Resistance (in this case, friction/damaging) eventually cause the vibration to stop

Fourier Transform

- Mathematical algorithm that decomposes any waveform into its frequency or phase components - Provides us w/ the spectrum, another way to graphically display a simple or complex sound - Plotted in the frequency domain • Amplitude spectrum • Phase spectrum

Myelination and nodes of Ranvier

- Schwann cells and oligodendrocytes form myelin - myelin increases action potential conduction velocity - nodes are breaks in the myelin sheath - spaces between myelin. exact spacing.

Tympanic membrane

- Medial boundary of external ear canal, lateral boundary of middle ear - Oval/cone-shaped relatively transparent membrane - About 55 - 90 mm^2 - Consists of 3 layers • Lateral side: epidermal lining of external ear canal • Medial side: mucosal lining (continuation of middle ear membrane) • Middle layer: supporting fibrous material

Ossicles - incus

- Medial to malleus: the "anvil" - Attached via the incudomalleolar joint - Body: occupies space in the epitympanic recess - 2 processes • Short process: next to body, located in epitympanic recess • Long process of incus: extends downward, almost parallel to manubrium of malleus • Lenticular process: rounded projection at end of long process, articulates w stapes via incudcostapdeial joint

Overview of CNS

- Meninges - Ventricular system - Rostral to caudal • Telencephalon • Diencephalon • Brainstem -- Mesencephalon, myelencephalon, metencephalon • Cerebellum -- Dorsal side of brainstem • Spinal cord

Classical psychophysical methods

- Method of limits - Method of adjustment - Method of constant stimuli

Brainstem

- Midbrain - Pons - Medulla - Cerebellum dorsal to pons - Neural signals from auditory signal propagate through several nuclei of these structures • Brainstem • Thalamus • Auditory cortex

MAP-C vs. MAF

- Minimum audible pressure (MAP) thresholds: audibility thresholds obtained w headphones/earphones • Sound level measured w a microphone & a coupler (object that approximates outer ear) - Minimum audible field (MAF) thresholds - obtained in free field, one meter from sound source • Sound played from speakers • Measured at location of head after obtaining threshold

MLDs Monotic

- Monotic: MmSm - Signal & masker presented to one ear, threshold obtained - Used as a reference for other conditions

Neural firing patterns

- More complex firing patterns in CANS than AN - Examples: • Onset/offset of sound • Changes in frequency/amplitude • Bands of noise instead of pure tones - Morphology (shape) of cells more variable

Pitch scale

- More difficult to quantify because other factors (such as intensity level) affect pitch - Example • Pitch of pure tones below 2000 Hz decreases w increasing level • Pitch of pure tones above 4000 Hz increases w increasing level

Tonal masking & the traveling wave

- Most efficient masker of a tonal signal (pure tone) would be a tone close to the signal frequency - Maskers w frequencies further away from the signal frequency (lower or higher) do not provide as much masking or possibly even no masking - Traveling wave of signal becomes "swallowed" by traveling wave of masker - The closer in frequency they are, the greater the overlap between the two traveling waves - Easier to mask out a higher frequency than a lower frequency: this is bc of the asymmetry of the traveling wave

Periodicity pitch

- Most stimuli w a periodic waveform will have a pitch equal to the reciprocal of the period - Periodicity pitch • (aka, fundamental frequency)

Hair cell system

- Motion of the traveling wave causes stereo cilia of hair cells to bend, or shear - Tops pivot clockwise/counterclockwise - Shearing triggers an electrochemical process that leads to transduction of sound into a nerve impulse - Mechanically gated K+ ion channels in the tops of the stereocilia • Normally closed - Tip links connecting tops of stereocilia (& body of kinocilium) - Cross links connecting body of stereo cilia so that they move together - When stereocilia are sheared AWAY from modiolus, ion channels OPEN - tips links stretch & "pull" them open • Like a trap door opening • Ion transport results in transduction of signal to nerve impulse - Ion channels close when stereocilia are sheared toward modiolus - tip links contract - Basilar membrane is attached at the spiral lamina - Tectorial membrane is attached at the spiral limbus - When membranes are displaced, pivot about 2 hinging points - Stereocilia of OHCs attached to underside of tectorial membrane - Pivot/rotate at base in response to opposite movement of BM & TM - Shearing action results - Mechanical method of shearing involving both membranes thought to only apply to OHCs - IHCs appear to not be attached to tectorial membrane • Shearing likely occurs as a result of fluid drag/movement between tops of hair cells & tectorial membrane • Enhanced by active mechanism of OHCs - Stereocilia are sheared toward or away from modiolus depending upon movement of the BM - When the BM is displaced UPWARD, the stereocilia are sheared AWAY from the modiolus - When the BM is displaced DOWNWARD, stereocilia are sheared TOWARD the modiolus

depolarization of hair cell

- Movement of the basilar membrane results in radial shearing between the tectorial membrane and the apical surface of the organ of Corti. - The tallest stereocilia on the OHCs are embedded in the tectorial membrane, the radial shear force is coupled directly to the stereocilia. - When the bundle of stereocilia is deflected toward the tallest stereocilia (away from the modiolus), tension is applied to the tip-links, which in turn pulls the mechanically gated channel open. - The opening of the channel allows ions in the endolymph (which bathes the stereocilia of the hair cells) to flow into the hair cell, leading to depolarization.

Postsynaptic potentials (PSPs)

- NT release causes the opening of ion channels —> ions can flow in or out depending on which channels have been opened - Postsynaptic potentials (PSP) - PSPs can result in depolarization or hyperpolarization - Excitatory post synaptic potentials (EPSPs) • Depolarizing - Inhibitory post synaptic potentials (IPSPs) • Hyperpolarizing - If membrane potential reaches threshold again another action potential will be initiated

Ion flow into and out of neuron during different stages of action potential

- Na+ channels open at the beginning of the action potential, and Na+ moves into the axon, causing depolarization. - Repolarization occurs when the K+ channels open and K+ moves out of the axon, creating a change in electric polarity between the outside of the cell and the inside

Define sound encoding

- Neural threshold: "threshold of hearing" for auditory nerve fiber - Threshold is defined as the sound intensity needed to raise the firing rate above the spontaneous rate

Rate-level functions

- Neural threshold: sound intensity level at which firing rate increases above SR - Saturation: level at which firing rate does not further increase - Dynamic range: range of sound levels over which firing rate will increase as sound level is increased • About 20 to 50 dB for most auditory neurons

Summary - Basic Neurophysiology

- Neuron components (soma, dendrite, axon) - Resting potential of neuron & threshold for action potential - Stages of action potential - Depolarization vs. repolarization vs. hyperpolarization - Refractory period (absolute vs. relative) - Myelin & saltatory conduction - EPSPs & IPSPs - Synapse

Electrophysiology of neuron

- Neuron maintains a resting potential of about -70 mV - Higher concentration of Na+ in extracellular fluid (outside of cell membrane) than inside cell - Higher concentration of K+ inside of cell than outside - Membrane contains voltage-gated ion channels • Ions can enter/exit the cell, changing the membrane potential

Nervous system: 2 main types of cells in nervous system —>

- Neurons: main cells for transmitting electrical signals through nervous system - Glia: Schwann cells, oligodendrocytes, astrocytes

Standing wave : node & antinode

- Node : the location on a standing wave where there appears to be minimum vibratory displacement - Antinode : the location on a standing wave w maximal vibratory displacement - The # of nodes & antinodes depends on the frequency of the vibration & the length of the enclosing space - Standing wave in a completely enclosed space (ex. Closed tube): • Standing wave w one antinode fundamental mode of vibration • Occurs when vibrating frequency has a wavelength that is twice the length of the tube • Fundamental frequency of vibration: -- f0 = c/2L - Frequencies needed to produce integer multiples of antinodes (1, 2, 3, 4, etc.) occur at integer multiples of fundamental vibrating frequency (2 f0, 3 f0, 4 f0, etc.)

White Noise : aperiodic complex sound

- Noise : a sound w/ an instantaneous amplitude that varies over time in a random manner - White noise : All frequencies between some limits are present at the same average intensity or pressure - Phase is distributed randomly

Pitch: Mel Scale

- Non musical - Mel scale • Reference sound: 1 kHz tone at 40 dB SPL defined to have a pitch at 1000 mels - Listeners are asked to scale the pitch value of the target sound relative to the pitch of the reference sound - 1 kHz - E.g. a sound w twice the pitch of 1000 mels is 2000 mels (though this DOES NOT necessarily correspond to 2000 Hz) - In general: • Doubling frequency (increasing by an octave) results in less than a doubling of pitch • An octave increase (doubling) in mid to high frequency range encompasses a greater range of pitch change than in low frequencies

Closed vs. open tube end

- Note that if the end of the tube is closed, a node appears there - If the end of the tube is open, an antinode appears there

Binaural listening advantage

- On average, we expect a 3-dB improvement in threshold when listening w two ears vs. one

How the message is passed

- Once AP reaches synaptic terminal, neurotransmitter is released into synaptic cleft - Neurotransmitters bind to receptors on postsynaptic neuron

Action potential - refractory period

- Once depolarization has reached threshold, another action potential cannot be initiated for a set amount of time - Sodium ion channels have to be reset - We call this the refractory period

Intensity encoding

- Once threshold has been reached, single auditory neurons will increase their firing rate w increases in sound intensity over a wide range (20 to 50 dB) - Above this range, firing rate remains constant or decreases slightly w further increase of intensity (plateaus) - Intensity encoding can be plotted w a rate-level function

Properties of a sine wave : Phase

- One cycle = one circular revolution - Revolution of a circle = 360, or 2pi radians - Starting phase is define as d(t) when t = 0 - Phase of 0 —> when d (t) = 0 & is followed by positive displacement • Ex: what phase is 0.0005 = 180 or pi - Waveforms can either be in-phase or out-of-phase w each other • In-phase - same phase -- Can have the same starting phase if different frequencies, but will not be in phase at all point in time • Out of phase : different starting phases, different instantaneous phases -- Ex: wave going up first —> starting phase = 0; wave going down first —> starting phase = 180

Hair cells

- One row inner hair cells: 3,500 - 3 to 5 rows outer hair cells: 12,000 - FINITE NUMBER OF HAIR CELLS: unable to regenerate (!!!)

Review - sine waves

- Only one (peak) amplitude, frequency & starting phase - Perceived as a pure tone • Pure tones don't exist in the norm environment

Traveling wave

- Originally studied by George von Bekesy in 1960s - studied mechanics of BM on cadavers - Updated w invention of the Mossbauer technique, which allowed visualization of TW in vivo

Transfer functions of outer ear

- Outer ear provides 10 - 15 dB natural amplification of sound from 1.5 - 7 kHz - Resonant frequency of adult outer ear canal: about 2.5 kHz - Resonant frequency of concha: about 5 kHz - Can help aid in localization

Difference in function between IHCs & OHCs

- Outer hair cells — depolarization leads (mostly) to activation of electromotility mechanism • Cochlear amplification - Inner hair cells — depolarization leads mostly to action potentials in afferent auditory nerve fibers • Signal transduction

Psychophysical methods: method of adjustment

- Participant is given control over stimulus property & asked to adjust it manually - Ex: press button when audible, release when not audible - Computerized algorithm to reverse the direction of the property (e.g. intensity) every time the participant's response changed from (+) to (-) or vice versa - Also an adaptive procedure

Pitch

- Perceptual attribute of sound, strongly correlated w spectral location of its frequencies

Anatomy/Physiology of the ear

- Peripheral auditory system • Outer ear • Middle ear • Inner ear (cochlea & vestibular organs) • Vestibulocochlear nerve - Central auditory nervous system • Various nuclei within CNS • Auditory cortex

Properties of sound : Phase

- Phase : the position of the object relative to resting state at any given point in time • A specific time such as 0.03, 12, etc. seconds - Starting phase : the initial position of the object prior to vibration • X-axis = 0; at the beginning - The oscillation of a sine wave is presented as revolution of a circle

Temporal encoding of frequency: phase locking

- Phase locking —> time locking of neural discharges to acoustic waveform - Neuron fires at the same phase of a cycle: follows amplitude peaks of a stimulus - If the neuron's firing pattern is preserving the timing of the stimulus, it is encoding the frequency of the stimulus - For high-frequency sounds, a neuron may not fire in a phase-locked manner at every cycle - Volley principle: other neurons are recruited to phase-lock & fire during other cycles - Neurons are staggered: overall temporal characteristics of waveform preserved - Phase locking (even volleyed) only occurs at frequencies up to 4/5 kHz. - Notice that the neurons fire only at the positive peaks of each cycle —> corresponding to rarefaction phases of stimulus when stereocilia are sheared - This is referred to as half-wave rectification

Intro to psychoacoustics/psychophysical methods

- Physical stimulus - Physiological processings/transduction - Perceptual experience (auditory perception)

Neural tuning curves

- Physiological tuning curves of the primary auditory fibers (auditory nerve) - The intensity of a sound needed to cause a neural fiber to just increase its firing above SR is indicated - Same shape! - Both neural tuning curves & psychophysical tuning curves are reflective of the patterns of the basilar membrane

Structures in outer ear

- Pinna (sometimes referred to as auricle) - External auditory meatus - External auditory canal - Leads to tympanic membrane, border between outer & middle ear

Temporal encoding of frequency: place encoding

- Place encoding —> specific neurons will be mostly easily stimulated by frequencies at/near CF - Firing rate will increase at/near CF - Firing rate can also increase w increasing intensity - Different frequency/intensity combinations will yield equivalent firing pattern rates (e.g., the entire tuning curve) - Place encoding is not enough: there has to be some other way to distinguish frequency

Head Related Transfer Function

- Plotted by measuring the difference in sound pressure level between source & at eardrum - Physical properties of head, torso, outer ear affect spectrum of resultant sound at eardrum

Electrical potentials

- Potential: an electric charge (can be positive or negative) - Direct current: electrical current that flows in one direction only • Only (+) or (-) - Alternating current: electrical current that reverses its direction

Structures of outer ear - pinna

- Primarily made of cartilage & skin; very few muscles, mostly nonfunctional - Many bumps & grooves, high individual variability - Angled about 15 to 30 degrees outward in humans

Review: neural tuning curve

- Primary auditory neurons (in the cochlear nerve) are tuned to a characteristic frequency - The sharper the tip of a tuning curve, the better the frequency selectivity - (Application: this leads to better clarity & better hearing in the presence of background noise)

Functions of middle ear

- Primary function: to overcome impedance difference between airborne vibration in outer ear & vibration of fluids in inner ear - Eustachian tube equalizes air pressure inside & outside the middle ear cavity - Recall: when sound encounters a change in impedance, it can be transmitted/diffracted, reflected, or absorbed - If the impedance of the successive medium is higher than that of the previous, most of the sound will be reflected - There is an impedance mismatch between outer & inner ear • Sound coming in would be attenuated by about 35 dB by the time it reached the inner ear

Intro to psychophysics Psychological perception:

- Psychological perception evaluated as a function of variation of different physical parameters of sound - Examples: • Intensity • Frequency • Timing/duration

Intro to psychophysics Psychophysics:

- Psychophysics: the study of the relationship between physical stimuli & the resulting perceptions/sensations • The study of sensory perception

tympanic membrane - middle fibrous layer

- Radial fibers: originate from center (more dense) & radiate to periphery of membrane (more sparse) - Circular fibers: surround membrane; more dense at periphery & more sparse in the center

Auditory sensitivity - dynamic range of hearing

- Range between absolute threshold of audibility & threshold of discomfort/pain - From approximately 0 dB SPL to 140 dB SPL at maximum sensitivity • 120-140 dB

Dynamic range of hearing

- Range between absolute threshold of audibility & threshold of discomfort/pain - From approximately 0 dB SPL to 140 dB SPL at maximum sensitivity • 120-140 dB

Resonance & Standing Waves

- Recall - standing waves can form in areas that are enclosed on one or both ends - Frequency of standing wave depends partially on length of tube/area - Frequency of standing wave - resonant frequency of tube - Driving force w small amplitude can produce vibration of increased amplitude at resonant frequency inside enclosed space

Resonance

- Recall that sound is created from the vibration of an object - Typically, an external force is needed to begin the vibration driving force - Every object has a natural or BEST vibrating frequency: resonant frequency • Minimal amount of driving force needed to cause object to vibrate at resonant frequency • Amplitude at the resonating frequency will be the greatest - Receiving object: resonator - In other words, the closer the frequency of the driving object to the resonant frequency of the receiving object, the easier it is to vibrate the receiving object - therefore, the HIGHER the amplitude • Swing has a tendency to go back & forth at a particular frequency • If you are pushing the swing, how do you make it go higher more easily? • There is a natural rhythm/timing to maximize the swing • When this happens, you are pushing at the resonant frequency - Most objects have a complex resonance pattern due to a complex physical structure • in other words, they may have multiple resonant frequencies.

Propagation of sounds

- Recall that sound originates from an object in vibration - We do not hear the vibration directly - the vibration sets off a chain reaction of moving molecules - Ultimately reaches the human ear & continues the vibrations at the eardrum - Molecules of the medium the object is in (for example, air) are disturbed/moved by the initial vibration - Air molecules immediately adjacent to object move in the direction of the vibration, & disturb the molecules adjacent to them - Begins a sound wave that propagates through the air caused by areas of molecules running into each other - Propagating medium must have mass & elasticity - Examples: air, water, iron - Vibrations can pass from one medium to another

Revisiting sound propagation

- Recall that when a force sets an object into vibration, a "sound wave" propagates away from it - This has been portrayed linearly • In actuality, it propagates in a spherical fashion in all directions - The amount of power created by sound is the same no matter the distance • Further distance —> power is divided amongst all -- Sound loses intensity w distance traveled

Critical band theory

- Recall: maskers w frequencies close to the signal are the most efficient at masking (result in greater masking) - Critical band theory: • There is a range of frequencies that affects the detectability of a signal • Outside of this range, frequencies present in the masker do NOT contribute significantly to masking

Purposes of outer ear

- Receive acoustic pressure waves & transmit to the middle ear - Aids in localization - Protects inner structures of ear from insects, foreign bodies - Can amplify some sounds (resonance!)

Sone scale

- Reference for sone scale • 1 sone = loudness of a 1000-Hz tone presented at 40 dB SPL • Therefore, 1 sone = 40 phons • Any sound that is 40 phons loud is 1 sone loud - A stimulus that is n sones loud is n times as loud as 1 sone - 2 sones is twice as loud as 1 sone - 3 sones is three times as loud as 1 sone & so on - Loudness in sones plotted as a function of dB SPL for a 1000 Hz tone - Above 30 phons, there is a doubling of loudness every 10 dB increase in level • doubling the sone scale value equates to about a 10-dB increase in intensity -- increase the tone 10 dB & you have essentially doubled the loudness

Depolarization of membrane

- Release of neurotransmitter opens ion channels - Open ion channels —> influx of positively charged Na+ - Leads to depolarization of membrane (occurs to neurons too!)

Periodic Complex Sound

- Repeats itself over time - The lowest frequency at which the sequence repeats itself is referred to as the fundamental frequency (f0) - The spectrum of a periodic complex sound may also contain energy at some or all harmonics - whole - # integers of the fundamental frequency - Referred to as a harmonic series

Basic rules of impedance

- Resistance is NOT frequency dependent (meaning, it opposes all frequencies equally) • Example of resistance - friction - Mass & stiffness reactance ARE frequency dependent • Overall impedance is different depending on frequency of sound • Mass reactance : opposes high frequencies more than low frequencies • Stiffness reactance opposes low frequencies more than high frequencies

Resonance & impedance

- Resonant frequency is determined by the physical properties of receiving object, or its impedance - The higher the mass reactance the lower the resonance frequency - Review of impedance: • Total opposition to flow of sound • Consists of resistance & reactance • Resistance is not frequency dependent • Reactance is frequency dependent

resonance : effects of impedance on resonant frequency

- Resonant frequency is determined by the physical properties of receiving object, or its impedance Review of impedance: • Total opposition to flow of sound • Consists of resistance & reactance • Resistance is not frequency dependent • Reactance is frequency dependent

Psychometric function

- Response rate can vary depending on the strength of whatever stimulus property you are measuring (let's use intensity as an example) - Response rate (50% heard, 60% heard, 90% heard) will vary depending on the intensity of a signal - This can be plotted as a function

Psychophysical Methods - Classical Methods: Psychometric function

- Response rate can vary depending on the strength of whatever stimulus property you are measuring (let's use intensity as an example) - Response rate (50% heard, 60% heard, 90% heard) will vary depending on the intensity of a signal - This can be plotted as a function

Cochlear potentials

- Resting potentials within the cochlea are created by presence of positively-charged ions • Resting potential —> base • Can be measured at rest —> w or w/out stimulus - Other cochlear potentials can be created by the presence of an incoming sound

Reticular Lamina

- Reticular lamina: ceiling above hair cells & supporting cells (stereocilia penetrate through) - Tight junctions between cuticular plate of hair cells, phalanges/tops of supporting cells - Separates endolymph from internal structures of organ of Corti & prevents mixing of cochlear fluids

Some important supporting cells/structures

- Rods of court: separate inner & outer hair cells (pillar cells) - Tunnel of corti: fluid space between pillar cells contains cortilymph (similar to perilymph) - Inner phalangeal cells: support base for IHCs - Deiters' cells: support base for OHCs • Top of cell has a cup-shaped structure that encloses OHC, w a phalange that contributes to reticular lamina - Cells of hens - Cells of Claudius

Eustachian tube

- Runs from anterior wall of middle ear cavity to posterior wall of nasopharynx at a downward angle of 45 - Superior 1/3 has a bony foundation, inferior 2/3 have a cartilaginous foundation - Normally closed (cartilaginous portion) • Can be opened by swallowing, chewing, yawning, etc. • Maintains pressure equalization between middle ear cavity & outside air environment

Cochlea - basilar membrane

- Runs length of cochlea: 35 mm - Narrower, thicker & stiffer at base (0.04 mm wide) - Wider & floppier at apex (0.36 mm wide) - Vibrates in response to fluid movement in scala media

Resting potential: endocochlear potential

- Scala media: filled w endolymph - High in K+, low in Na+ +80 mV - Highest resting potential in the body - Generated/maintained by stria vascularis

Summary: Auditory

- Sensitivity/Thresholds & Loudness Perception Absolute threshold & sensitivity - Minimum audibility curve • MAP • MAF - Dynamic range of hearing - dB SPL vs. dB HL - Temporal integration - Loudness quantification - Phon scale • Equal loudness contours - Sone scale • 10 dB —> doubling loudness except at low intensities - Loudness recruitment - Loudness adaptation

Action potentials

- Signals are transmitted between neurons via events called action potentials - All-or-nothing events

Temporal masking - Simultaneous masking

- Simultaneous masking: when signal & masker occur at the same time (simultaneously)

Temporal masking simultaneous

- Simultaneous masking: when signal & masker occur at the same time (simultaneously) - Masking can occur when signal & masker do not occur at the exact same time

Complex waveform formula

- Sine wave • d(t) = Asin(2πft + Φ) • One amplitude, frequency, & starting phase - Complex wave • dtotal= d1+ d+ 2+ d3+ ... + dn • d(t) = A1*sin(2*π*f1*t + Φ) + A2*sin(2*π*f2*t + Φ2) + ... + An*sin(2*π*fn*t + Φn)

Adding sine waves

- Sine waves are added by summing the amplitude of vibration at each point in time - If the individual waves have the same frequency, the resultant waveform will still be a pure tone but may look different if phase/amplitudes are different

Binaural masking terminology

- Sm: signal presented to one ear - Mm: masker presented to only one ear - So: signal presented binaurally with no interaural differences - Mo: masker presented binaurally with no interaural differences - Sπ: signal presented to both ears, 180° out of phase - Mπ: masker presented to both ears, 180° out of phase • Assumed: signal = pure tone; masker = wideband noise

tympanic membrane - pars flaccida

- Smaller area (1/3) in the superior portion of TM; contains fewer fibers overall, more flaccid - Surrounded by ligament called annulus

Thresholds of audibility

- Smallest level of sound detectable by a person w/ normal hearing as a function of frequency - High threshold: lower (less) sensitivity • More hearing loss - Low threshold: higher (more) sensitivity

Classical maths of psychophysics can lead to participant bias

- Solutions • You can add no-stimulus trials to gauge false positive/false negative responses (participant answers yes/no) • This way you can also take into guessing/bias behaviors • Calculate total percent correct out of all types of trials - Forced-choice paradigm • Example: two interval forced choice

w/ calculator Solve for x : X = log(6)42

- Solve for x • X = log(6)42 • 6^x = 42 • Log (6^x) = log 42 • X log 6 = log 42 • Divide both sides by log (6) • X = 2.086

The neuron

- Soma: cell body • Contains nucleus, cytoplasm, etc. - Dendrites - processes, extensions of cell body • "Tree-like" structures • Receive incoming synaptic connections from other neurons or receptor cells (such as hair cells!) • Direct signals toward axon - Axon - long process on opposite end of cell body from dendrites • Longer/thinner than dendrites • Initial segment, axon, synaptic bouton • Neural signals propagate down axon - Many axons in CNS & PNS are wrapped by substance referred to as myelin, cell membranes layered on top of each other • Helps action potential propagate down axon more quickly - Synapse/synaptic cleft: gap between end of axon (synaptic bouton) & next neuron (dendrite) - Neurons exchange information through release of neurotransmitters

Interaural Time Differences (ITD)

- Sound arrives at one ear earlier than the other when originating away from horizontal midline - Different timing of arrival —> different phases at each ear - Phase difference will depend on: • Azimuth • Frequency - Notice - not much change in ITD over range of higher freqs - Increase in ITD for increased azimuth - Notice that ITDs taper off at higher frequencies - ITDs are a better cue for localization at low frequencies

Central auditory nervous system

- Sound initially encoded by fibers of auditory nerve - Neural signals travel through brainstem to auditory cortex - Structures afferent to auditory nerve considered central auditory nervous system - Auditory signal transmitted through various "stations" in central nervous system (brainstem up to brain) - Both excitatory & inhibitory - Largely afferent pathways • Efferent auditory pathways as well - Tonotopic organization preserved at each location

Properties of sound

- Sound is created by vibrations • An object moving back & forth - Sound can be classified by its physical properties as well as its perceptual properties - Sound is created by vibrations of objects in our everyday world - Vibrations create pressure waves, which propagate through a medium (such as air) • Travel through the air until it reaches a source (ear) - Pressure waves are received & perceived by the auditory system as sound

ILDs in Lateralization

- Sound is lateralized toward the ear receiving sound with higher intensity level - Able to effectively utilize ILD cues at lower frequencies for lateralization (under headphones) than for localization (in free field)

Cocktail party effect

- Sound sources may be separated spatially which allows for better detection as well as attention - Cocktail party effect : ability to identify/attend to a sound in a complex and noisy environment when spatial separation exists - Intact function of brainstem needed

Filters

- Special types of resonators that can modify the incoming frequency components of vibrations - Will vibrate to some incoming frequencies, but not others - Frequencies to which filter will vibrate are considered to be passed : amplitude of filter vibration is equal to driving force - Other frequencies will be attenuated : amplitude of filter vibration at these frequencies is reduced

Cochlea

- Spiral-shaped portion of the inner ear within bony labyrinth (membranous labyrinth) - Approximately 2.75 turns around a central axis: modiolus - Modiolus houses neuron of the auditory branch of the vestibulocochlear nerve (CN VIII) - Spiral lamina: bony shelf projecting outward from modiolus into cochlea - Inside of bony labyrinth = 3 channels • Scala vestibuli - superior • Scala media - cochlear duct - middle (membranous labyrinth) • Scala tympani - inferior - Oval window: a membrane-covered opening forming the lateral entrance to seal vestibuli (where stapes footplate is positioned) - Round window: a membrane-covered opening inferior to the oval window that forms the lateral entrance to scala tympani - Reissner's membrane: separates scala vestibuli from scala media - Basilar membrane: separates scala media from scala tympani - Basilar membrane attaches to spiral lamina & attaches at the spiral ligament - Cochlea bounded on outer wall by stria vascularis & then spiral ligament • Stria vascularis provides primary blood supply to cochlea & produces endolymph (replenishes K+)

Spontaneous firing rate

- Spontaneous activity - neural activity (firing rate) that occurs at rest, without stimulus • Range from 0 to 100 spikes per second - Used as a baseline to compare against neural activity occurring in response to a stimulus

Condensation

- Stapes footplate displaced INWARD from oval window —> condensation - Basilar membrane displaced DOWN - Stereocilia are deflected toward modiolus —> K+ channels close - No K+ influx (& hair cells expel K+) - Hyperpolarization —> increased potential difference between hair cell & endolymph

Rarefaction

- Stapes footplate displaced OUTWARD from oval window —> rarefaction - BM displaced UP - Stereocilia are deflected away from the modiolus —> K+ channels open • Ion channels are open - K+ influx into the hair cell body —> depolarization • (-) inside, (+) outside

Active cochlear mechanics

- Stereocilia of outer hair cells are imbedded in tectorial membrane - OHCs contract & expand in length w movement of BM (through prestin, a protein) • Increases displacement of BM at characteristic frequency - Results in amplification of sound at the CF - At low/mid sound intensity levels, active amplification created at characteristic frequency, providing sharper frequency tuning - We call this the cochlear amplifier - Note that this only happens at peak of the traveling wave!

Psychophysical methods: method of constant stimuli

- Stimuli are presented at several selected fixed levels (e.g. 12 dB, 8 dB, 4 dB) - Many trials are presented at each level presented in random order (4 dB, 12 dB, 10 dB, 8 dB) - Participant responds w "yes" or "no" after each presentation (we call this a "yes/no paradigm")

Inner hair cell

- Structurally stronger than OHCs, stronger stereocilia - Flask-shaped - 35 μm in length - 50 to 70 stereocilia per cell, several rows (also graded in length) - Stereocilia form a wide "U" pattern

Ventricular system

- Structures containing cerebrospinal fluid (CSF) throughout the CNS • Lateral ventricles • Third ventricle • Fourth ventricle

Timbre

- Subjective attribute that differentiates two or more sounds w the same pitch, loudness, & duration - Ex. Cello vs. violin - Related to bandwidth of complex stimulus (especially harmonics)

Anatomical orientations

- Superior (above) - Inferior (below) - Posterior (behind) • Dorsal (back) - Anterior (in front of) • Ventral (belly) - Medial • Near midline - Rostral • Toward the head - Caudal • Toward the tail

Central Auditory Nervous System - superior olivary complex

- Superior olivary complex —> brainstem - From CN, fibers project both ipsilaterally & contralaterally to superior olivary complex - 2/3 fibers decussate: cross over through trapezoid body - About 1/3 gibers project ipsilaterally First place in the auditory nervous system that receives information from the other side - Group of nuclei clustered in the pons - First place where binaural (both sides of auditory system) information is represented - Major functions include: - Localization Efferent regulation of auditory system - Stapedial/tensor tympani acoustic reflex

Auditory cortex — temporal lobes

- Superior temporal gyrus: heschl's gyrus - Higher-level auditory processing Processing of speech & other complex signals

Hypothesized Mechanisms for Backward Masking

- Temporal masking may reflect the difference in the latencies (timing) of the neural impulses encoding the signal versus the masker - More neurons are firing in response to the masker than to the signal due to the difference in energy - An increase in the number of neurons firing causes a "head start" in neuron transmission, so perception of masker gets there "faster" the impulses representing the masker reach the central nervous system in advance of the impulses representing the signal

Low SR fibers

- Tend to saturate at higher intensity levels

High SR fibers

- Tend to saturate at lower intensity levels

Middle ear muscles

- Tensor tympani muscle: inserts into neck of malleus • Originates from anterior wall of tympanum • Innervated by CN V (trigeminal nerve) - Stapedius muscle: attaches at the head of the stapes • Originates from posterior wall of tympanum • Innervated by a branch of CN VII (facial nerve) - When muscles contract, they pull the 2 ossicles in opposite directions - Acoustic reflex: muscle contraction in response to loud sounds • Stiffens ossicular chain, prevents much of sound from transmitting through • Protection from loud sounds

Diencephalon

- Thalamus - Hypothalamus

Masking - Upward spread of masking

- The 1000Hz pure tone can mask signals w higher (upward) frequencies more readily than those with lower frequencies, which peak toward the apex. - Said another way, low frequencies can mask high frequencies much more readily than high frequencies can mask low frequencies. - The phenomenon of upward spread of masking has implications in speech understanding in background noise - The low frequency content of the background noise can interfere w hearing for lower intensity high frequency sounds, such as consonants.

Elasticity

- The ability of an object to return to its resting state after disturbance: elasticity

Middle Ear Acoustic Reflex

- The acoustic reflex is triggered by a combination of the sound's intensity & bandwidth (range of frequencies present), which the observer perceives as loudness. When an observer perceives the sound at a sufficient loudness level, the reflex is triggered - When sound is loud enough to trigger a reflex, the stapes muscles will receive nerve impulses from the lower brainstem, & the contraction occurs

Sound Shadow effect

- The amount of sound reflected also depends on the size of the object it encounters - If object is: • Smaller than the wavelength, then sound wave will bend around it & move past it w/out being affected -- diffraction • Much larger than wavelength, then sound will be mostly reflected • Reflection creates a shadow effect (an area of reduced sound energy directly behind the reflecting source) Shadow effect - Based on that fact, will LOW or HIGH frequencies have a greater tendency for diffraction around interfering objects? - Based on that fact, will LOW or HIGH frequencies have a greater tendency for reflection around interfering objects?

Impedance - the overall opposition to the propagation of sound

- The amount of sound reflected vs. transmitted vs. reflected depends on the difference in impedance between the two media • The greater the difference in impedances, the more sound will be reflected (i.e., the less will be transmitted) - Composed of two things: reactance & resistance - Two forms of reactance: • Mass reactance • Stiffness reactance (remember, stiffness is the opposite of elasticity) - Impedance of the medium is therefore dependent on its mass & elasticity/stiffness - Impedance - the overall opposition to the propagation of sound. - Z = √[R^2 + (Xm - Xs)^2] • Z = overall impedance • R = resistance • Xm = mass reactance • Xs = stiffness reactance

BM displacement is asymmetrical

- The asymmetry of the traveling wave is preserved in the auditory neuron - Remember, the traveling wave dissipates immediately after reaching its peak

Nonlinearity of active mechanics

- The cochlear amplifier activates more for low/moderate intensities than for high intensities - Additional sounds are generated as a distortion byproduct of active mechanics

d(t) = Asin(2πft + Ө)

- The equation relating the properties of the simple vibration on an object set in motion can be described as : d(t) = Asin(2πft + Ө) • d(t) = instantaneous displacement at time t • A = maximum amplitude • F = frequency • T = time • Ө = starting phase

Inverse square law

- The farther away one is from a sound source, the softer the sound becomes - In other words, increased distance leads to decreased intensity/sound pressure level. - Review: Intensity is the rate at which power is transferred over a defined area • The area of a sphere: Ar = 4πr^2 • r = radius of the sphere (in other words, the distance from the sound source to the point of measurement) - Therefore: I = P / 4πr^2 • This formula helps us find intensity • Sound travels in spherical direction • each time you double the distance (r), you are distributing the same power over an area FOUR TIMES AS LARGE • when you doubled distance from a sound source, you will DECREASE intensity by a factor of 4 -- 10(log 1/4) = -6 dB ---- Decrease of 6 decibels —> (- 6 dB) - Intensity is also proportional to pressure squared • I ∞ p^2 - Pressure is inversely proportional to distance (as opposed to distance squared). Therefore, if distance is doubled, pressure will decrease by a factor of 2. - If the distance from a sound is doubled, then sound intensity will decrease by a factor of 4 for sound intensity, & 2 for sound pressure - 10 log (1/4) = -6 dB - 20 log (1/2) = -6 dB - Doubling the distance —> 20 log (1/2) = -6 dB - You can extrapolate this formula such that you can calculate the amount of sound lost w any increase in distance: • e.g., traveling from 1 to 8 m: • 20 log (1/8) = -18.06 dB -- *always use 20 log (x)*

Sine wave

- The formula is the graphical function of a sine wave : describing the simplest form of periodic oscillation - Energy at only one frequency - Also referred to as simple harmonic motion - Perceived as a pure tone - X axis : time (abscissa) - Y axis : displacement (ordinate) Waveform - A graphical representation of a vibration (such as sound) displayed as the displacement as a function of time

Characteristic frequency (CF)

- The frequency corresponding to the place on the BM where displacement will be maximum - Every place on the basilar membrane has a different characteristic frequency

membranous labyrinth fluid composition

- The membranous labyrinth is filled with endolymph - its potassium ion concentration is higher than its sodium ion concentration

Psychophysical Methods - Classical Methods: Method of Limits

- The method of limits is used by the clinical audiologist in determining "the limits" of the patient's hearing thresholds. - When finding the hearing threshold using the method of limits, the frequency of tone is set, then the intensity is adjusted by the audiologist or experimenter, & the patient or subject responds, one hopes, as instructed. - These responses are noted & used to define the threshold, which clinically is the lowest intensity that the patient responds to at least 50% of the time

Longitudinal waves

- The molecules do NOT keep traveling through the air, but rather are pulled back toward rest position (recall elasticity) - Inertia causes molecules to overshoot their mark the other direction - & so on - Areas of condensation (when molecules are close together, w/ increased density & pressure) & rarefaction (when molecules have increased distance between them, w/ decreased density/pressure) are created

Ossicles - malleus

- The most lateral ossicle, connects directly to the TM - "hammer" - Medial to the TM - Head, neck, & 3 processes • Manubrium - longest process, attaches to TM • Anterior process • Lateral process

Cochlear nerve structure

- The neurons of the cochlear nerve innervate the base of the hair cells within the cochlea - Exit scala media through habenula perforata & form the spiral ganglion inside the modiolus - Fibers exit cochlea radially & become the auditory nerve trunk - course through opening in temporal bone - internal auditory canal - One branch of the vestibulochlear nerve, CNVIII • Course toward brainstem

Lateralization

- The perception of location at ears/head when listening under headphones or earphones - Difficult to separate ITD/ILD variables to examine them separately in free field - Cannot entirely control factors - Lateralization experiments involve presenting sound via headphones - Can more directly manipulate ITD/ILD independently - Sounds presented through headphones with ITD (usually interaural phase difference, IPD) or ILD imposed - Listener will typically hear one fused sound w a location that moves according to the ITD/ILD

Quantifying changes in loudness

- The phone scale allows us to compare sounds of equivalent loudness - It does not allow us to quantify changes in the perception of loudness - For this, we utilize the sone scale

Resonance of outer ear

- The physical structures of the outer ear will somewhat alter the frequency response of the incoming sound • Resonance = the natural or vast frequency - less force is needed to drive the frequency in comparison to other frequencies - Ear canal (partially closed tube!) will generally amplify sounds between 2000 - 3000 Hz (standing wave fundamental frequency) - f0 = c/4L

Transduction

- The process of converting one type of energy to another - Acoustical —> mechanical —> chemical —> neural/electrical

1st law of exponents

- The product of 2 exponents w a common base is equal to the base raised to the addition of the exponents • A^b x A^C = A (b+c) • Ex: 2^2 x 2^3 = 2(2+3) = 2^5 = 32

2nd law of exponents

- The ratio (division) of 2 exponents w a common base is equal to the base raised to the subtraction of the exponents - A^b/A^c = A(b-c) - Ex: 2^5/2^3 = 2(5-3) = 2^2 = 4

membranous labyrinth scalae vestibuli, media, tympani

- The scala vestibuli communicates (con- nects) directly with the vestibule. - The scala tympani communicates with the scala vestibuli at the apex of the cochlea, at the helicotrema. - These two membranes, basilar and Reissner's, delineate the scala media. - The scala media is the membranous labyrinth within the cochlea

Critical bandwidth calculations

- The shape of the critical band (also referred to as an auditory filter) reflects that frequencies close to the signal has greater masking importance than frequencies farther away from the signal - The total area under the curve represents the masking that can affect perception of a particular frequency - We can convert this to a rectangle w equivalent area to more easily define bandwidths of a critical band

Speed of sound & stiffness/density

- The speed of sound in air ~ 343 m/s (default value used for practice problems) • Not a constant value -- dependent on temperature, density, stiffness, & humidity - Stiffness : the ability of an object to resist being deformed —> greater stiffness results in increased speed of sound - Density : space between molecules —> greater density results in decreased speed of sound - Ultimately the stiffness/density relationship will drive the speed of sound

Critical band theory: internal filter

- There is an "internal filter" centered on the frequency of a signal - total noise power inside that filter determines the amount of masking - Frequencies outside of the boundaries of this filter do not affect our ability to detect the signal

Masking w Noise/Critical Band - critical band theory : Internal auditory filters

- There is an "internal filter" centered on the frequency of a signal - total noise power inside that filter determines the amount of masking - Frequencies outside of the boundaries of this filter do not affect our ability to detect the signal

Meninges

- Three membranous layers enclosing CNS • Dura mater • Arachnoid • Pia mater

Threshold performance

- Threshold as a continuous number along a performance curve - You may report hearing a very soft sound 5/10 times but might report hearing a louder sound 9/10 times - Chance performance vs. ceiling performance

threshold trial vs. run

- Thresholds are estimated & typically averaged over many repetitions - Trial: one repetition, stimulus provided, response obtained - Run: series of trials over which responses are averaged

The issue w the minimum audibility curve for clinical practice

- Thresholds for "normal hearing" listeners originally obtained at the Wisconsin state fair in 1954 (graph) - Inherent differences in hearing sensitivity across thresholds - The dB hearing level scale was developed to set an "audiometric zero" baseline

Auditory sensitivity - threshold : "Missing 6 dB"

- Thus, a sound is louder when reproduced by loudspeaker compared to headphones, while the level at the ears are the same in both cases. - This phenomenon was called the "missing 6 dB". - It was found using methods of direct comparison between loudspeaker & headphone reproductions

Purpose of middle ear

- To convert acoustic pressure waves from the air into mechanical vibrations (transaction from acoustic to mechanical energy) - To help overcome the impedance mismatch between the outer environment & the inner ear • Air vs. fluid

Type of maskers

- Tones - Noise - Speech - Anything interfering w the signal

Basic terminology

- Tracts: traveling neural fibers grouped into pathways - Nuclei: groupings of nerve cell bodies where fibers synapse (the "stations") - Information processed at each nucleus, then cells send processed information to next nucleus along pathway - Complex pathways: neural tracts may not always synapse at every nucleus, may skip some altogether, etc. - Neural tracts course ipsilaterally (same-sided) & contralaterally (crossing over to opposite side) - Therefore, both sides of the brainstem/brain are eventually stimulated by input to one ear — binaural stimulation

Function of inner ear

- Transduction of acoustic signal from mechanical energy ultimately to neural impulses at the auditory nerve - Provides nervous system w information about frequency, intensity, & timing (duration, phase) content of acoustic signal

Head related transfer function (HRTF)

- Transfer function specifically comparing output at sound source & at outer ear

Auditory system

- Transforms the acoustic pressure waves traveling through the adjacent medium into neural impulses that we ultimately perceive as sound

Otoacoustic Emissions (OAEs)

- Very soft sounds that can be measured in the ear canal w a microphone - By-product of the electromotility of the outer hair cells - Can only be measured if a cochlear amplifier is functional! - Clinical applications in newborn hearing screening & audiology test battery

Organs of balance (vestibular system)

- Vestibular inner ear: involved in balance & spatial orientation - Transduces head movement into neural signals - Utricle: process horizontal linear acceleration - Saccule: process vertical linear acceleration - Semicircular canals: process angular movement • Posterior • Anterior • Horizontal

Review --> The inner ear: mechanical physiology

- Vibrations in oval window result in fluid displacement which leads to displacement of basilar membrane - Movement of basilar membrane = traveling wave which propagates from base toward apex - Peak displacement is at characteristic frequency (CF), & traveling wave dissipates quickly at more apical regions - Mass-stiffness gradient of basilar membrane creates tonotopic organization in the cochlea - Passive cochlear mechanics do not explain human frequency selectivity. - Amplification at the CF is created by electromotility of the outer hair cells (cochlear amplifier). - The cochlear amplifier is considered a nonlinear mechanism, & also generates byproduct sounds called otoacoustic emissions.

Fluid displacement leads to membrane vibration

- Vibrations of stapes footplate against oval window displace fluids inside cochlea - Basilar membrane vibrates as a direct result of fluid movement - Fluid displaced at oval window displaces round window - Pressure changes in scala vestibuli as a result of stapes movement into oval window - Pressure of scala vestibuli higher than scala tympani - Scala media is displaced DOWNWARD -- toward scala tympani - Fluid movement passes through helicotrema & continues through scala tympani until it reaches the round window - Direction of fluid displacement reverses as stapes moves out of oval window; round window moves inward - Pressure in scala tympani higher than scala vestibuli - Scala media is displaced UPWARD - toward scala vestibuli

Examples of tube w one closed & one open end

- Vocal tract • Males have bigger vocal tract —> have lower pitch - Outer ear canal

Sound propagation what is a wavelength?

- Wavelength - the distance between successive areas of condensation or rarefaction; the distance between peaks of a sound wave - Wavelength is dependent upon the frequency of the sound & the speed that sound travels through that particular medium

Critical band theory: overlapping

- We listen to signals through overlapping internal filters - Frequencies outside of the boundaries of this filter do not affect our ability to detect the signal

Differential Sensitivity - Intensity discrimination

- Weber's Law applies best to wide-band noise - Threshold for ∆I decreases slightly for pure tones as level increases - Wideband noise almost follows Weber's law ("near miss"); better than for tones - the smallest detectable change is a constant fraction of the intensity of the stimulus

Summary: Differential sensitivity & pitch perception

- Weber's Law of Discrimination • Formula: ∆S/S = k - Frequency discrimination • Weber's Law applies across range of frequencies, k = .002 (approximately) • Frequency discrimination improves at higher intensity levels - Intensity discrimination • Weber's Law generally applies - near miss as level increases. Best for wideband noise. - Temporal discrimination • Increase of proportion of temporal increment needed for discrimination observed • Mathematically does not obey Weber's Law • Dependent upon other stimulus factors - Pitch perception: based on changes in frequency, but is also affected by duration, intensity, & complex spectral characteristics - Mel scale: 1000 Hz tone at 40 dB SPL = 1000 Mels - Pitch of missing fundamental can be perceived in complex sounds - Timbre is based on pitch perception w similar fundamental frequency

Frequency discrimination

- Weber's fraction fairly consistent - From about 400-4000 Hz: - About k = .002

Differential Sensitivity - Frequency discrimination

- Weber's fraction fairly consistent - From about 400-4000 Hz: - About k = .002 - our ability to detect a change in the frequency of a pure tone & is expressed as a percentage w respect to the reference frequency

Weber's Law

- Weber's law of discrimination: a stimulus must be increased by a constant proportion of itself to be perceived as just different - Discovered w weights: easy to distinguish 1-pound from 2-pound weight, more difficult to distinguish between 100 & 101 lbs. - ∆S/S = k • Also called the weber fraction - S = value of base or standard stimulus - ∆S = increment of change needed fro just-noticeable differentiation (S2 - S1) - K = a constant

Front-Back/Vertical Localization

- What about front/back localization? • A sound directly in front of the head will have the same ITD/ILD as from the same distance behind the head. - All sounds located along mid-sagittal plane will have equal ITDs & ILDs • Cone of confusion - Ultimately, we are still less effective at vertical than horizontal localization

Considerations (threshold)

- What are the factors that can influence the outcome of finding a threshold? • Repetition (getting the average) - Human factors: experience, fatigue, attention, motivation, "neural noise" - Tradeoff between accuracy & efficiency

Interference

- What happens when a sound wave strikes an object? - Change in properties of the traveling medium - Therefore, a change in impedance (the overall opposition to the propagation of sound)

Practice problems - complex periodic sound What is the 7th harmonic of a periodic sound w a fundamental frequency of 123 Hz? If the 8th harmonic of a sound is 364 Hz, what is the fundamental frequency?

- What is the 7th harmonic of a periodic sound w a fundamental frequency of 123 Hz? • 7 x 123 = 861 Hz - If the 8th harmonic of a sound is 364 Hz, what is the fundamental frequency? • 364/8 = 45.5 Hz

Temporal masking - Backward masking

- When masker comes on & off after occurrence of signal

Types of temporal masking: backward masking

- When masker comes on & off after occurrence of signal

Temporal masking - Forward masking

- When masker comes on & off prior to occurrence of signal

Types of temporal masking: forward masking

- When masker comes on & off prior to occurrence of signal

Action potential - depolarization

- When positive ions enter the cell, the membrane potential is DECREASED - (i.e., less negative) —> depolarization - Once depolarization has reached a certain threshold of depolarization (-55 to -40 mV), the action potential is initiated at the initial segment of the axon - All-or-none principle: if depolarization does not reach threshold, the neuron will not fire (i.e. no action potential) - Initial depolarization & rapid depolarization: caused by SODIUM COMING IN to cell - Action potential will reach its peak depolarization

Psychophysical Methods - Classical Methods: Method of Adjustment

- When subjects are allowed to adjust the stimulus themselves, a method of adjustment is being used - Typically, the intensity increases smoothly rather than going up so many decibels each step, & the signal stays on even if it's not audible to the subject. - The subject could adjust the signal by manipulating a knob, moving it left & right until threshold is reached

Rarefaction vs condensation

- When the air molecules are temporarily un- usually close together, we say they are "compressed" or "in the compression phase." - The terms "condensation" and "condensation phase" are synonymous - the pressure is increased in this phase of vibration - when the air molecules are spread apart, they are in rarefaction

Action potential - repolarization

- While sodium is coming in, potassium is leaving the cell - Eventually, sodium will stop coming in & potassium will continue leaving the cell - When potassium leaves, this creates repolarization: cell membrane potential becomes more negative

Impedance

- Z = √ R^2+(2πfm -s/[2πf])^2] - Z = overall impedance - R = resistance - m = mass - s = stiffness

formulas : impedance

- Z = √[R^2 + (Xm - Xs)^2] • Z = overall impedance • R = resistance • Xm = mass reactance • Xs = stiffness reactance

reticular lamina

- a layer of extracellular material containing a fine network of collagen protein fibers that "belongs to" the underlying connective tissue - deep to basal lamina, network of collagen fibers

summating potential

- a sustained, direct current (DC) shift in the endocochlear potential that occurs upon stimulation of the organ of Corti by sound -The source of the summating potential is unclear, but the Inner Hair Cells may be a key player

Formula relating wavelength & frequency

- c = fλ, or λ = c/f - f = frequency - c = speed of sound in the medium of question, in meters/sec - λ = wavelength (in meters)

formulas : wavelength & frequency

- c = fλ, or λ = c/f - f = frequency - c = speed of sound in the medium of question, in meters/sec - λ = wavelength (in meters)

supporting cells organ of corti

- cells that insulate, support and protect neurons - There are 3 more support cells of interest. - Cells of Hensen are found on the stria vascularis side of the outer hair cells. - There is a space be tween the outer hair cell & the Hensen cells. - The cell type changes as the location becomes closer to stria vascularis; these are cells of Claudius. - At the base of the cochlea, there are cells beneath the cells of Claudius, called Boettcher cells

physiology of basilar membrane

- coiling from base to apex. - the hair cells are tightly packed rather than standing freely

Auditory sensitivity - dB SPL vs dB HL

- decibel hearing level (dB HL) & the decibel sensation level (dB SL). - The SPL notation is used when we are measuring the physical intensity of a sound, that is, stating how much sound energy is present irrespective of whether anyone or anything can or does hear it

Complex Periodic Sound

- f1 = 1st harmonic =1*F0 - f2 = 2nd harmonic = 2*F0 - f3 = 3rd harmonic = 3*F0 - ... - fn = nth harmonic = n*F0 - In a complex periodic sound, the energy in an amplitude spectrum appears at discrete frequencies relating to the fundamental frequency (infinite #) - When this happens, we refer to this as a line spectrum • (As opposed to a continuous spectrum, where there are not discrete frequencies of energy)

tip links and cross links

- filaments that connect Stereocilia to each other - On sides of stereocilia - Help stereocilia to move in concert when sound stimulation is present - Open pores to allow potassium to enter cells

Middle ear eustachian tubes function

- it is the only source of air for the middle ear. - Normal middle ear function requires air pressure to be equal on both sides of the tympanic membrane. - As atmospheric pressure changes (e.g., going up a mountain road), & as the tissues of the middle ear absorb air, it is necessary to replenish the air, or to equalize the air pressure in the middle ear, on a periodic basis. - The second function of the eustachian tube is to provide an exit for mucus or other material that collect in the middle ear.

Masking w Noise/Critical Band - Noise terminology : signal to noise ratio (SNR)

- level of noise (in dB) subtracted from level of signal (in dB) • Ex: 60 dB tone, 70 dB noise = -10 dB SNR

middle ear ossicles

- malleus (hammer), - incus (anvil), - stapes (stirrup)

Action potential - hyperpolarization

- repolarization will actually overshoot original resting potential - Hyperpolarization - Can last a few hundred milliseconds

The middle ear overcomes the impedance mismatch between the outer and inner ear through which of the following mechanisms?

- the area difference between the tympanic membrane and the oval window. - the lever action of the ossicles. - the buckling action of the tympanic membrane. *all of the above.*

Auditory Sensitivity - threshold : Minimum Audibility pressure

- the level of a tone presented via headphones at the threshold of audibility. - The level (in decibels sound-pressure level) is the inferred or measured pressure at the tympanic membrane. - Also called minimum audible pressure

Review of logarithms what is a log? how is it read?

- the logarithm of a # is the exponent by which the base has to be raised to produce that # - Example: • Y = a^x • X = logaY - To take the logarithm (or log) of a # is to solve for the exponent - Example: • Log(2)8 Read as : log base 2 of 8 • 2^? = 8 2 raised to the power of what # equals 8? • Answer : 3

Absolute and relative refractory periods

- the period immediately following the firing of a nerve fiber when it cannot be stimulated no matter how great a stimulus is applied—called also absolute refractory phase; - compare relative refractory period the period shortly after the firing of a nerve fiber when partial repolarization has occurred and a greater than normal stimulus can stimulate a second response—

directional shearing action of stereocilia

- the stereocilia are bent toward their kinocilium on one side and away from their kinocilium on the other side. - Shearing of the stereocilia toward the kinocilium causes a depolarization of the receptor potential & an increase in afferent action potentials.

Auditory Sensitivity - threshold : Minimum Audibility field

- the threshold for a tone presented in a sound field to a participant who is not wearing headphones. - The participant faces the sound source, & the threshold intensity is measured at the midpoint of the head

Masking - Psychophysical tuning curve (PTC)

- to obtain a psychophysical tuning curve (PTC), a pure-tone signal is used as the probe. - The shorthand Fp means frequency of the probe, & Lp the level of the probe. - To obtain a PTC, the probe stays constant at that Fp and Lp. - Narrowband noises at different center frequencies are used to mask the probe

Properties of voltage-gated channels

- voltage-dependant: open/close depending on membrane potential - time-dependent: open/close during a certain time under a certain membrane potential

Numerical data in acoustics

- we will often have to manipulate either very small or large #s - Ex: the pressure levels of sound - Just barely audible —> 20 uPA, or 0.000002 Pa - Uncomfortably loud —> 20,000,000 uPa or 20,000,000,000 Pa

Band-reject filter

- will pass sinusoidal components w frequencies above & below two cutoff values - Frequencies between cutoff values are attenuated Filter Characteristics

High-pass filter

- will pass sinusoidal components w frequencies above a certain cutoff value - Frequencies below cutoff value are attenuated

Low-pass filter

- will pass sinusoidal components w frequencies below a certain cutoff value - Frequencies above cutoff value are attenuated

Band-pass filter

- will pass sinusoidal components w frequencies between two cutoff values - Frequencies above & below cutoff values are attenuated

The characteristic frequency (CF) of a psychophysical tuning curve (PTC)

- will usually correspond to the signal frequency being presented. - is located at the lowermost tip of the curve. - is indicative of the masker frequency that needs the least intensity to mask a signal of the particular frequency being tested. *All of the above.*

Auditory filter bandwidth increases:

- with the loss of the cochlear amplifier. - at higher intensity levels. *All of the above.*

Differential Sensitivity - Weber's Law - ∆S/S = k

- ∆S/S = k • Also called the weber fraction - S = value of base or standard stimulus - ∆S = increment of change needed for just-noticeable differentiation (S2 - S1) - K = a constant

Transfer functions

-Amplitude/phase spectra of incoming sounds are altered by the physical characteristics of the head, torso, & outer ear structures - Transfer function: graph describing sound pressure changes as a result of intervening structures

Each point on the minimum audibility curve represents the corresponding lowest threshold sound pressure level at each frequency. What value in dB HL do each of these points equate to?

0 dB HL

A moving object travels a distance of 3 meters in 4 seconds. What is its velocity?

0.75 m/s work: - distance/time - 3/4 unit: m/s

The absolute refractory period of a neuron is

1 msec

Hypothesized Mechanisms for Forward Masking

1. "Ringing" of BM persists after masker has been presented 2. Short-term adaptation or fatigue in auditory nerve/CANS, which reduces response to signal 3. Neural activity created by masker persists in the CANS 4. Suppression of tone perception by efferent system

How does the middle ear make up for this impedance mismatch? : 3 major ways

1. Area differential between TM & stapes footplate • Effective area of TM: 55 mm^2 • Area of stapes footplate: 3.2 mm^2 • 55mm^2 / 3.2 mm^2 = 17 : 1 ratio - What happens when the same force is applied cross a smaller area? • Pr = F / A • Sound pressure is increased from tympanic membrane to stapes by a factor of 17 • 20 log 17 = 25 dB amplification 2. Lever action of ossicles • Manubrium/neck of malleus are longer than long process of incus • Lever action is 1.3:1 - force is increased by 1.3 at stapes 3. Buckling action of TM • TM buckles as it vibrates due to conical shape • Further increases force by a factor of 2 • Total approximate increase in pressure • 17 x 1.3 x 2 = 44.2 • 20 log 44 = 33 dB

Action potential - review

1. Depolarization of initial segment 2. Threshold reached (typically between -55 & -40 mV) 3. Rapid continuation of depolarization up to about +30 mV 4. Repolarization 5. "Overshoot" of resting potential - hyperpolarization 6. Restoration back to resting potential

Review: filters

1. Filter type - low-pass, high-pass, band-pass, or band-reject 2. Cutoff frequency - border frequency where attenuation begins to occur 3. Roll-off or rate of attenuation - slope of attenuation • Ex. 6 dB per octave, 10 dB per octave • The higher the rate of attenuation, or the steeper the roll-off (i.e., steeper slope) - the more precise the filter - Not necessarily physical objects - Electrical circuits - Analog or digital - Also alter the phase of the sound waves passing through - Time delay in passing through the filter

Practice Questions 1. If a person is speaking at 50 dB SPL, what is the absolute measure of pressure present? 2. If a sound exhibits 1.54 x 10^-4 W/m^2, what is its intensity level in dB?

1. If a person is speaking at 50 dB SPL, what is the absolute measure of pressure present? First, determine what units to work w/ • SPL = sound pressure level • 50 dB SPL = 20log( X Pa / 2*10^-5 Pa) Now, solve for X • 50 dB SPL = 20log( X Pa / 2*10^-5 Pa) • [divide by 20] Now rearrange the equation • 10^2.5 = X / 2•10^-5 316.23 = X / 2•10^-5 --> X = 6.32 x 10^-3 Pa 2. If a sound exhibits 1.54 x 10^-4 W/m^2, what is its intensity level in dB? dB IL = 10log( 1.54x10^-4/ 10^-12 W/m^2) = 10log(1.54x10^8) = 81.88 dB IL How do dB SPL compare to dB IL? How are they related?

Cochlear potentials Four cochlear potentials:

1. Resting potentials 2. Cochlear microphonic 3. Summating potential 4. Compound action potential

Stages of an action potential

1. depolarization 2. repolarization 3. hyperpolarization

So how can we graph these simple & complex sounds? How can the individual components be identified easily?

1.Time domain • Waveform - plot of displacement, pressure, or intensity as a function of time • Time on the x-axis 2.Frequency domain • Plotted on the Fourier transform

Humans have the best auditory sensitivity (lowest threshold) at which of the following frequencies?

1000 Hz

Simple sound - Hz

1000 Hz Pure Tone

According to Weber's Law of Discrimination, what frequency would be determined "just noticeably different" from a tone with a frequency of 1000 Hz? Assume that the Weber fraction k = .002.

1002 Hz

Quantitive Measurements : 1st law of exponents

1st Law of Exponents • The product of two exponents w/ a common base is equal to the base raised to the addition of the exponents. • A^b x A^c = A(b+c) • Ex. 2^2 x 2^3 = 2(2+3) = 2^5 = 32

quantitive measurements : 1st law of logarithms

1st Law of Logarithms • log(a*b) = log a + log b Example: • log(10*2) = log10 + log2

quantitive measurements : 2nd law of exponents

2nd Law of Exponents - The ratio (division) of two exponents w/ a common base is equal to the base raised to the subtraction of the exponents. • A^b / A^c = A(b-c) • Ex. 2^5 / 2^3 = 2(5-3) = 2^2 = 2 x 2 = 4

inner ear: semicircular canals

3 fluid filled semicircular canals - At right angles to each other - Contain hair cells (crista) affected by movement - Bending of hair cells generates impulses by vestibular branch of 8th cranial nerve to cerebellum

If a sound is determined to be three times as loud as a 1000 Hz tone at 40 phons, how many sones is that?

3 sones

Calculate the equivalent rectangular bandwidth for a center frequency of 3000 Hz using the following formula: ERBN = 24.7 (4.37F + 1)

348.517 Hz

quantitive measurements : 3rd law of exponents

3rd Law of Exponents • An exponential term A^b raised to some power c is equal to the base A raised to the product of the two exponents b & c. • (A^b)^c = A(b*c)

What is the loudness level of a 1000-Hz tone with an intensity level of 40 dB SPL?

40 phons & 1 sone

Calculate the overall sound level intensity for 66 dB IL + 55 dB IL

66 dB IL = 10 log ( Ix1 / 10^-12 W/m^2) 6.6 = log (Ix1 / 10^-12 W/m^2) Ix1 = 10^6.6 • 10^-12 W/m^2 Ix1 = 3.981 • 10^-6 W/m^2 55 dB IL = 10log ( Ix2 / 10^-12 W/m2) 5.5 = log (Ix2 / 10^-12 W/m^2) Ix2 = 10^5.5 • 10^-12 W/m^2 Ix2 = 3.163 • 10^-7 W/m^2 Ixtotal = Ix1 + Ix2 dB ILtotal = 10 • log ([Ixtotal / 10^-12 W/m^2) = 10log ([3.981 • 10^-6 W/m^2+3.163 • 10^-7 W/m^2]/ 10^-12 W/m^2) = *66.332 dB IL*

What is the absolute pressure for a sound w/ a sound pressure level of 70 dB SPL?

70 dB SPL = 20 log( X / 2 • 10^-5 Pa) 3.5 = log (X / 2 • 10^-5 Pa) 10^3.5 = X / 2 • 10^-5 3162.27766 = X / 2 • 10^-5 X = *.06324 W/m^2, or 6.324 • 10^-2 W/m^2*

Psychophysical Methods - threshold : absolute vs. differential

A "threshold" refers to the minimum level of a stimulus that can be detected (absolute threshold) or the minimum change in a stimulus that can be detected (difference threshold).

outer ear transfer function

A graph of the measurement of how much a sound has been attenuated or amplified as it passes through a system (such as a hearing aid or the outer & middle ear) is called a transfer function. A transfer function tells us how the spectrum would be altered as the sound is transmitted (transferred) through the system

tectorial membrane

A membrane located above the basilar membrane; serves as a shelf against which the cilia of the auditory hair cells move

Inner Ear: Cochlea

A spiral-shaped cavity of the inner ear that resembles a snail shell and contains nerve endings essential for hearing.

basilar membrane

A structure that runs the length of the cochlea in the inner ear and holds the auditory receptors, called hair cells.

Reissner's membrane

A thin sheath of tissue separating the vestibular and middle canals in the cochlea.

How can the following expression be rewritten? y = logax.

A. a^y = x

basic properties of sound physical properties for sound sources = mass & elasticity

All sound sources must have mass & elasticity. • Mass - the amount of matter present in an object as characterized by weight & density (inertia) • Elasticity - the ability of an object to return to its original state after a force has been exerted on it • Inertia & elasticity counter each other

sound propagation : rarefaction & condensation

Areas of condensation (when molecules are close together, w/ increased density & pressure) & rarefaction (when molecules have increased distance between them, w/ decreased density/pressure) are created

Which of the following sounds will have a CONTINUOUS (i.e., non discrete) amplitude spectrum?

An aperiodic complex cound

Which of the following is true about modern adaptive psychophysical testing?

An estimate of a psychophysical threshold is calculated by averaging the value associated with several reversals.

Intensity encoding

As the intensity, or magnitude of the signal entering the ear increases, the number of neural impulses sent to the brain increases and their magnitude is greater. The greater neural activity corresponds to greater sound intensity

Psychophysical Methods - Psychoacoustics Paradigms

Auditory detection: - perceive the vowels, consonants & sometimes, the stress pattern of what is spoken Auditory discrimination: - the ability to hear & distinguish between environmental sounds Auditory identification: name what was heard - by repeating, writing, or pointing to text or a picture

An input complex sound with frequency components at 1000, 1500, 3000, and 6000 Hz at equal amplitudes is passed through a filter system. The resulting sound still contains components at these four frequencies only, but the amplitudes at 1500 and 3000 Hz have been attenuated. What type of filter was the sound passed through?

Band Reject

Organ of Corti

Center part of the cochlea, containing hair cells, canals, and membranes

Central Auditory Nervous System - Ipsilateral/contralateral projections

Contralateral: Of or pertaining to the other side. Ipsilateral: the same side.

Differential Sensitivity - difference threshold

Difference threshold = just noticeable difference (jnd) or difference limen (DL) - The term limen is a synonym for threshold - difference thresholds are frequently referred to as difference limens. - Another term that means the same thing as difference limen is just notice able difference (JND). - The difference limen for intensity (DLI) is the smallest intensity change that the observer can detect 50% of the time. (Of course, the 50% criterion assumes a method of limits or method of adjustment threshold.

You listen to two separate recordings of people singing "The Star-Spangled Banner." Although the pitches of each performance are exactly the same, you can easily tell the difference between the two singers. Explain why.

Different timbre created by different amplitudes of harmonics etc.

basic properties of sound : displacement

Displacement - the amount of movement away from state of equilibrium at any given point in time

Inner Ear: Vestibule

Encloses saccule and utricle Receptors provide sensations of gravity and linear acceleration

Post-synaptic potentials - excitatory and inhibitory (EPSPs and IPSPs)

Excitatory postsynaptic potentials (EPSP) bring the neuron's potential closer to its firing threshold. Inhibitory postsynaptic potentials (IPSP) change the charge across the membrane to be further from the firing threshold. Postsynaptic potentials are subject to spatial and temporal summation

forumla for force

F = ma Force is measured in Newtons, or N1 N = 1 kg*m/s^2

Newton's Third Law of Motion

For every action there is an equal & opposite reaction - The forces of two bodies on each other are always equal & directly opposite.

Frequency/temporal encoding

For neurons encoding stimuli with a single time. scale: a temporal encoding scheme is one in which. there is significant additional correlation between. the relevant stimulus parameter and any moments. of the elicited spike pattern having higher order

Which of the following statements is NOT true regarding auditory differential sensitivity?

Frequency discrimination is NOT affected by overall sound intensity level.

You are conducting a replication of Patterson's notched-noise band experiment in an attempt to learn more about your significant other's critical bands. You play a 2000 Hz tone in the presence of a band-reject noise with a notch centered at 2000 Hz and obtain an absolute threshold for the signal. You then decrease the width of the notch, maintaining the same overall level of the masker. What do you expect to occur?

If the noise has entered into the frequency region of the critical band, then the threshold will INCREASE.

Endocohlear potential

If you compare the charge of endolymph with that of perilymph, you are measuring the endocochlear potential, which is about +100 mV. Another name for the resting endocochlear potential is endolymphatic potential.

sound propagation : impedance (resistance, mass reactance, stiffness reactance & effects on frequency)

Impedance - the overall opposition to the propagation of sound • The amount of sound reflected vs. transmitted vs. reflected depends on the difference in impedance between the two media - The greater the difference in impedances, the more sound will be reflected (i.e., the less will be transmitted) Impedance - the overall opposition to the propagation of sound • Composed of two things: reactance & resistance • Two forms of reactance: - Mass reactance - Stiffness reactance (remember, stiffness is the opposite of elasticity) • Impedance of the medium is therefore dependent on its mass & elasticity/stiffness Impedance - the overall opposition to the propagation of sound. Z = overall impedance R = resistance Xm = mass reactance Xs = stiffness reactance Z = √[R^2 + (Xm - Xs)^2] Basic rules of impedance • Resistance is NOT frequency dependent (meaning, it opposes all frequencies equally) - Example of resistance - friction • Mass & stiffness reactance ARE frequency dependent - Overall impedance is different depending on frequency of sound - Mass reactance - opposes high frequencies more than low frequencies - Stiffness reactance - opposes low frequencies more than high frequencies

properties of an action potential

Is an "all or none" event: resting potential either passes threshold or doesn't Has a fixed amplitude: AP's don't change in height to signal information Has an absolute refractory period in which stimulation will not produce an AP (limits the firing rate)

If a sound has a sound pressure level that is NEGATIVE, what does this mean?

It means that the pressure of the sound in question is smaller than the chosen reference pressure.

Which of the following is NOT true about the impedance of a sound source?

It only contains resistance

Over a large range of intensity levels, loudness perception appears to follow what pattern?

Loudness doubles with every 10 dB increase in sound intensity.

resonance : filters

Low-pass filter - will pass sinusoidal components w/ frequencies below a certain cutoff value High-pass filter - will pass sinusoidal components w/ frequencies above a certain cutoff value Band-pass filter - will pass sinusoidal components w/ frequencies between two cutoff values Band-reject filter - will pass sinusoidal components w/ frequencies above & below two cutoff values

Central Auditory Nervous System - Auditory cortex

MGB —> auditory cortex: - Auditory tract fans out into auditory radiations to project to auditory cortex Auditory cortex — temporal lobes: - Superior temporal gyrus: heschl's gyrus - Higher-level auditory processing - Processing of speech & other complex signals

Outer Ear: external auditory meatus

Narrow chamber in the temporal bone - Lined with skin - Ceruminous (wax) glands are present - Ends at the tympanic membrane

A psychoacoustics participant sits in a booth wearing headphones. The participant is given active control over the ability to increase and decrease the level of the sound according to what is heard. This psychophysical method is referred to as the:

Method of Adjustment.

A psychoacoustics participant sits in a booth wearing headphones. An experimenter adjusts the level of a sound playing through the headphones by decreasing it slowly, and the participant is instructed to press a button when she believes that she no longer hears the sound. The experimenter then adjusts the sound to increase its level, and the participant is instructed again to indicate when she believes she hears the sound again. The method of psychophysics utilized here is referred to as the:

Method of Limits.

middle ear muscles

Muscles attached to the ossicles in the middle ear. The smallest skeletal muscles in the body, they contract in response to very intense sounds & dampen the vibration of the ossicles.

What substance allows an action potential to propagate faster down the length of an axon (i.e., saltatory conduction)?

Myelin

Central auditory nervous system - peripheral vs. central auditory system

Peripheral auditory system: - Outer ear - Middle ear Inner ear (cochlea & vestibular organs) - Vestibulocochlear nerve Central auditory nervous system: - Various nuclei within CNS - Auditory cortex

saltatory conduction

Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of membrane.

The structure that separates scala vestibuli from scala media is

Reissner's membrane.

resonance : rate of attenuation

Roll-off or rate of attenuation - slope of attenuation - Ex. 6 dB per octave, 10 dB per octave - The higher the rate of attenuation, or the steeper the roll-off (i.e., steeper slope) - the more precise the filter

Auditory sensitivity - Sensitivity to duration/temporal integration

Sensitivity to duration : - Hearing sensitivity improves as sound duration increases - Lower threshold Temporal integration : - Below this range, level of sound must be increased for equivalent detection - We refer to this ability of the auditory system to assimilate sound energy over time as temporal integration

Example: masking

Signal: 1000 Hz tone Which masker is best (most effective)? 1. 1003 Hz 2. 822 Hz 3. 506 Hz 4. 1600 Hz - Closest one —> low —> high

Localization cues are thought to be mediated at which structure of the auditory system?

Superior olivary complex.

Newton's Second Law of Motion

The acceleration of an object depends on the mass of the object & the amount of force applied.

inner ear: traveling wave

The cochlea's traveling wave appears to grow as the wave moves apically, then diminishes very quickly and will not vibrate the basilar membrane farther up (that is, more toward the apex and away from the point of maximum up & down displacement) because of the mass/stiffness gradient of the basilar membrane

A psychoacoustic experiment is conducted in which two sounds of the same frequency and starting phase are played through headphones to a consenting listener. The sound entering the right headphone speaker is 30 dB SPL and the sound entering the left headphone speaker is 40 dB SPL. Which of the following is true?

The listener will lateralize the sound to the left.

A psychoacoustic experiment is conducted in which two sounds of the same frequency and starting phase are played through headphones to a consenting listener. The sound is adjusted so that the intensity level is equal across both ears, but the starting phase of the sound entering the right headphone is 0 degrees and the starting phase of the sound entering the left headphone is 90 degrees. Which of the following is true?

The listener will lateralize the sound to the right.

True or false. The decibel scale compresses the range of absolute intensity and/or pressure values in order for them to be more easily manipulated in calculations.

True

resting potential of neurons -- sodium vs. potassium

The negative charge within the cell is created by the cell membrane being more permeable to potassium ion movement than sodium ion movement. In neurons, potassium ions are maintained at high concentrations within the cell while sodium ions are maintained at high concentrations outside of the cell.

middle ear: methods of overcoming impedance mismatch

The middle ear has a mechanical design that increases the force of the vibration of the foot- plate of the stapes. Two different types of mechanical advantage are used in what amounts to a passive (no source of cellular energy required), or mechanical, amplification system. These two systems are (1) the lever effect of the ossicular chain & (2) the areal ratio of the tympanic membrane & the oval window.

middle ear main function

The middle ear is principally designed to ensure that sound efficiently enters the fluids of the inner ear. There is a loss of sound energy when the sound waves enter the dense cochlear fluids. The ear acts as a mechanical amplifier to boost the sound energy so that this loss is of no consequence

outer ear main functions:

The outer ear enhances mid-to high-frequency sound through its resonance characteristics

electromobility of outer hair cells

The outer hair cells mechanically amplify low-level sound that enters the cochlea. The amplification may be powered by the movement of their hair bundles, or by an electrically driven motility of their cell bodies

Outer Ear: External Auditory Canal

The passageway that directs sound waves from the auricle to the tympanic membrane.

What is the primary function of the Eustachian tube?

The primary function of the Eustachian tube is to equalize air pressure inside and outside the middle ear cavity.

Depolarization vs hyperpolarization

The process during the action potential when sodium is rushing into the cell causing the interior to become more positive. The movement of the membrane potential of a cell away from rest potential in a more negative direction.

According to Newton's Law, force can be calculated as

The product of mass and acceleration.

differential pressure between scala vestibuli/tympani

The scala vestibuli and scala tympani contain perilymph whereas the scala media contains endolymph. The scala vestibuli and scala tympani are continuous with sound waves travelling up the vestibuli and returning through the tympani.

According to the critical band theory, we process auditory stimuli through internal band-pass filters.

True

An action potential can be initiated when a neuron has been hyperpolarized (during its relative refractory period).

True

There is a 6 dB decrease in both intensity level and sound pressure level when the distance from a sound source is doubled.

True

True or false. A complex sound can carry an infinite number of frequencies.

True

Type I vs. Type II fiber characteristics

Two types of fibers • Radial fibers - Type I fibers • Outer spiral fibers - Type II fibers Type I fibers • Comprise 90-95% of the auditory nerve fibers • Exclusively innervate inner hair cells • Each neuron only innervates 1-2 IHCs • Each IHC may be innervated by 16-20 type I fibers- Many-to-one innervation • Thicker than type II fibers Type II fibers • Comprise 5-15% of the auditory nerve fibers • Mostly innervate OHCs- "One-to-many" innervation - 1 fiber innervates about 10 hair cells • Basal end of cochlea -- innervate outermost row of outer hair cells • Toward apex -- innervate middle and innermost rows of OHCs

Examples (weber's law)

What is the weber fraction (I.e., the constant k) for two handbells that are 100 lbs & 110 lbs - k = ∆S/S - k = (110 - 100 lb) / 100 lb • S1 is the smallest value - k = 10 lb / 100 lb - = 0.1

Practice questions : - What would be the period of a 500 Hz sine wave? - If a sine wave has a period of 400 milliseconds, what is its frequency?

What would be the period of a 500 Hz sine wave? • 1/500 = .002 seconds If a sine wave has a period of 400 milliseconds, what is its frequency? • Convert 400 milliseconds to seconds • 400 ms x 1 sec/1000 ms —> 400/1000 = 0.4 sec • 1/0.4 = 2.5 Hz - Note that the shorter the period, the higher the frequency, & vice versa - This is referred to as an inverse relationship

formulas : exponents/scientific notation

X^0 = 1 X^1 = X X^-y = 1(X^y) A^b • A^c = A (b + c) A^b/A^c = A (b - c) (A^b)^c = A(b • c)

formulas : logs

Y = a^X X = logaY logaA = 1 loga1 = 0 logaA^x = X 1st law log (a • b) = log a + log b 2nd law log (a/b) = log a - b 3rd law loga^b = b • loga

tuning curve

a graph of the responses of a single auditory nerve fiber or neuron to sounds that vary in frequency and intensity

filters: band pass

a limited range of frequencies is transmitted

Psychophysical Methods - Other Psychoacoustical Methods : Direct scaling/matching methods

a procedure for developing numerical scales of magnitude of psychophysical factors in which the observer makes judgments of the magnitude of stimuli

filters: band reject

allows all frequencies to pass except those in a certain range

The external auditory canal, in fully-grown adults, is shaped like

an S

Psychophysical Methods - Other Psychoacoustical Methods : Adaptive/staircase method

an algorithm that actively adjusts the stimuli on-line in response to the subject's performance

tonotopic organization

an arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency

Newton's first law of motion

an object in motion will remain in motion unless acted upon by another force

____________ is proportional to the square of _______________. options: Intensity, pressure Pressure, intensity Force, velocity Displacement, pressure

answer: intensity, pressure

anatomical orientations anterior/posterior

anterior: in front of or front posterior: in behind of or behind

bony labyrinth spiral lamina

bony shelf known as the bony or osseous spiral lamina. The nerve cells exiting the cochlea go through holes in the osseous spiral lamina

What frequency is "heard" as the pitch when listening to a complex periodic sound?

c. The fundamental frequency.

The outer (lateral) one-third of the external ear canal is lined with ________.

cartilage

bony labyrinth modiolus

center core, of the cochlea

Neurotransmitters

chemical messengers that cross the synaptic gaps between neurons

outer ear (pinna)

collects sound from air and directs it through the ear canal

One of the distinctive landmarks of the tympanic membrane that can be observed with a microscope or otoscope in the anterior/inferior quadrant is referred to as the ______________ .

cone of light

Middle Ear: Eustachian Tube

connects the middle ear & the pharynx. It equalizes air pressure on both sides of the eardrum

Which plane divides a body into anterior/posterior sections?

coronal

formulas : sine wave

d(t) = Asin(2πft + Ө) • d(t) = instantaneous displacement at time t • A = maximum amplitude • F = frequency • T = time • Ө = starting phase

basic properties of sound : equation for simple vibration of object

d(t) = Asin(2πft + Ө) • d(t) = instantaneous displacement at time t • A = maximum amplitude • f = frequency • t = time • Ө = starting phase

Which method of psychophysics is needed to generate an entire psychometric function (with all thresholds observed over a range of stimulus changes)?

d. Method of constant stimuli

The audiogram displays auditory thresholds in

dB HL

2.0 * 10^-9 W/m^2

dB IL = 10 log (2.0 • 10^-9 W/m^2 / 10-12 W/m^2) = 10log (2.0 * 103) = *33.010 dB IL*

formulas : decibel dB IL/db SPL

dB IL = 10log (x/[10^-12 w/m^2]) dB SPL = 20log (x /[2 • 10^-5Pa])

How much sound intensity is lost between 2 & 3 meters from a sound source?

dB IL = 20 • log (3/2) = 3.52 dB IL lost, OR = 20 • log (2/3) = -3.52 dB IL

4.566 * 10^-3 W/m^2

db IL = 10log (4.566 • 10^-3 W/m^2 / 10^-12 W/m^2) = 10log (4.566 • 10^9) = *96.59 dB IL*

Absolute thresholds to sounds:

decrease with increased tone duration up to 250-500 ms.

A head-related transfer function demonstrates that the amplitude of sound does not change between the original sound source and the level by the time it reaches the tympanic membrane.

false

intercellular resting potential

difference in charge from endolymph to the hair cells as a "voltage drop" of about 170 mV for the outer hair cells and 140 mV for the inner hair cells.

The smallest magnitude of difference that allows a person to discriminate between two nearly identical stimuli is referred to as a(n)

differential threshold.

anatomical orientations dorsal/ventral

dorsal: towards the back of the body ventral: towards the front of the body

What structure maintains pressure equalization between the middle ear cavity and outside air environment?

eustachian tube

Distortion Product OAEs

evoked by two continuous pure tones presented to the ear -Two stimulus tones close in frequency f1. lower frequency f2. higher frequency Ratio of higher frequency to lower frequency f2/f1=1.20 Stimulus tones are presented simultaneously at moderate intensity levels usually in the range of 55 to 65 dB SPL Usuallly recorded across a frequency range of 500 to 8000 Hz Largest DPOAEs occur at 2f1-f2= 2x lower frequency mins the higher frequency

formulas : fundamental frequency of vibration

f0 = c/2L f0 = c/4L --> frequency has a wavelength 4 times the length of space

The lateral 1/3 of the external auditory canal is lined with bone and does not contain glands to produce cerumen.

false

The impairment of signal detection by a masker that is presented entirely before the onset of the signal is referred to as known as

forward masking

In general, what physical characteristic of sound most strongly correlates with our perception of pitch?

frequency

function of neurons and glia

glial cells provide support and protection to the neurons (nerve cells), maintain homeostasis, cleaning up debris, and forming myelin. They essentially work to care for the neurons and the environment they are in.

anatomical planes transverse

horizontal plane at right angles to the sagittal & frontal planes, slicing the body into a superior (upper) & inferior (lower) portions

Scalar vs. vector

length (L) : scalar quantity - standard metric - units often used • Kilometer (km) = 1000 m = 10^3 m • Centimeter (cm) = .01 m = 10^-2 m • Millimeter (mm) = .001 m = 10^-3 m • Micrometer (μm) = .000001 m = 10^-6 m Displacement (d) : vector • Specific application of length referring to magnitude of an object's change in position (movement) • Has magnitude & direction --> vector Mass : scalar • Standard metric unit - kilogram (kg) • Other units often used : • Gram (g) = .001 kg • Milligram (mg) = .000001 kg, or .001

standing waves can occur

in a tube enclosed at one end. in a tube enclosed at both ends. *All of the above*

At its characteristic (best) frequency, an auditory neuron will

increase its firing rate at the lowest intensity compared to other frequencies

rate-level function

increasing the level of the acoustic stimulus and measuring changes in the discharge rate of the single neuron above the spontaneous rate

A waveform

is a plot of displacement as a function of time

A complex aperiodic sound

is composed of a sum of simple sine waves

anatomical orientations lateral/medial

lateral: away from median medial: towards the median

What are the two types of cells in the nervous system?

neurons & glia

inner hair cells

neurons in the organ of Corti; responsible for auditory transduction

Masking w Noise/Critical Band - Noise terminology broadband noise

noise containing a large range of frequency components

Neurons with HIGH characteristic frequencies are more likely to be located

on the outside of the auditory nerve bundle.

The primary sensory end organ of hearing in the cochlea within the inner ear is referred to as the _______________.

organ of corti

The stapes footplate creates vibrations through the

oval window

spontaneous firing rates

periodic production of action potentials by a neuron in the absence of synaptic input

Endolymph is high in _________ and low in ___________.

potassium; sodium

Which of the following quantities is considered a VECTOR?

pressure

Outer ear Cerumen (earwax)

provides a number of benefits. - mildly antibacterial, - noxious to insects, - helps to keep the skin of the canal & tympanic portion of the canal are glands, which secrete membrane from drying out.

firing rates of sensory neurons

provides the brain with information on the intensity of a sensory stimulus

Masking w Noise/Critical Band - Noise terminology : bandwidth

quantified range of frequencies in a sound (highest frequency - lowest frequency)

neuronal dynamic range

range of sound levels over which firing rate will increase as sound level is increased

filters: high pass

remove low frequency energy

filters: low pass

removing the high frequency energy is accomplished

anatomical orientations rostral/caudal

rostral: towards the front of the brain caudal: towards the tail

What anatomical plane divides a structure into left and right halves?

sagittal

anatomical planes sagittal/midsagittal

sagittal: slicing it longitudinally into right & left parts midsagittal: vertical plane passing through the centre of the body (midline) that cuts it longitudinally into right & left halves

middle ear tympanic membrane

semitransparent membrane that separates the external auditory canal & the middle ear cavity

Threshold

smallest increment of parameter at which a person is able to detect presence of or difference in stimulus (some specified percentage of the time)

Differential threshold

smallest magnitude of difference that allows a person to differentiate between two nearly identical stimuli - Also referred to as discrimination

resonance - Effects of impedance on resonant frequency

some frequencies mass reactance is limiting the vibration, & at frequencies below the resonant frequency stiffness reactance limits vibration. Change the frequency & you change the total impedance. Examine Figure 5-3. Here, frequency is changed & total impedance is measured. At three frequencies, we examine the components of impedance.

A graph that depicts a sound in the frequency domain is referred to as a

spectrum

Differential Sensitivity - Weber's Law of Discrimination

states that the size of the just notice ably different change in pressure divided by the pressure of the original sound is always a constant fraction

The basal end of the basilar membrane is more _________; therefore, it is maximally displaced when stimulated by ___________ frequencies.

stiff; high

Psychophysical Methods - psychophysics

study of all sensory perception

Psychophysical Methods - psychoacoustics

study of the perception of sound

Masking w Noise/Critical Band - Noise terminology : total power

sum of amplitudes of all sinusoids in spectrum of noise

Anatomical orientations Superior/inferior

superior: towards the top of the head inferior: towards the feet

rate of attenuation

the act or process of attenuating something or the state of being attenuated: such as. a : a lessening in amount, force, magnitude, or value : weakening -- the rate of being lost

The minimum audible pressure curve (MAP-C) is a graph that shows:

the average thresholds of an adult with normal hearing as a function of frequency under headphones.

passive vs active cochlear mechanics

the cochlea can be modeled as a series of radial sections ranging from the base to the apex. The resonant frequency of each section is based on the average mass, stiffness, and damping of the basilar membrane at that section

What landmark can be found in the anterior inferior quadrant of the tympanic membrane?

the cone of light

threshold

the level of stimulation required to trigger a neural impulse

neural threshold

the minimum potential needed to stimulate an action potential

The shape of the psychophysical tuning curve (PTC) indicates that:

the most effective masking frequency is located at or near the signal frequency.

Masking w Noise/Critical Band - Noise terminology : spectrum level

the power per hertz of a sound, usually expressed in decibels sound-pressure level (dB SPL)

High vs. low spontaneous rates and threshold/saturation

the state in which a neuron predominantly outputs values close to the asymptotic ends of the bounded activation function

Which of the following statements is NOT true about simple sine waves?

through rare, they can occur naturally in the world

Different types of quantities : time

time (t) - scalar quantity - standard metric unit : second (s) - units often used : • millisecond (ms) = .001 s = 10^-3 s • microsecond (us) = .000001 s = 10^-6

bony labyrinth habenula perforata

tiny holes in the spiral lamina through which auditory nerve fibers pass

anatomical planes coronal

vertical plane at right angle to the sagittal plane that divides the body into anterior (front) & posterior (back) portions

Find the absolute pressure associated with 45 dB SPL.

work: - 45 dB SPL - 45 dB SPL = log 20 (x/2 • 10^-5) - divide both sides by 20 - 2.25 = log (x/2 • 10^-5) - 10^2.25 = (x/2 • 10^-5) - (10^2.25)(2•10^-5) answer: - 0.003556 - 3.556 •10^-3

Find the overall sound intensity level for 50 dB IL + 50 dB SPL + 70 dB IL.

work: - 50 dB IL + 50 dB IL + 70 dB IL - 50 = log 10 (x/10^-12) - 10^5 = (x/10^-12) - 1 • 10^-7 - 70 = log 10 (x/10^-12) - 10^7 = (x/10^-12) - 1 • 10^-5 - log10 (1 • 10^-7 + 1 • 10^-7 + 1 • 10^-5)/10^-12) answer: - 70.068 dB IL

What is the fifth harmonic of a complex periodic sound with a fundamental frequency of 320 Hz?

work: - 5th harmonic, f0 = 320 - 5 • 320 answer: = 1600 Hz

Based on the formula provided below, calculate the critical bandwidth (officially, the equivalent rectangular bandwidth) for an auditory filter centered around 2000 Hz. F is indicative of the center frequency in KILOHERTZ.

work: - ERBN = 24.7 (4.37F + 1) - 24.7 (4.37(2) + 1) answer: 240.6 Hz

If a sine wave has a period of .75 milliseconds, what is its frequency (rounded to the nearest integer)?

work: - F = 1/p - convert .75 ms into sec. - .75/1000 = 7.5 • 10^-4 - 1/7.5 • 10^-4 answer: = 1333 Hz

If a sound wave propagating through the air has a frequency of 4000 Hz, what is its wavelength? Assume the speed of sound in the air is 343 m/s.

work: - λ = c/f - c = 343 - f = 4000 Hz - λ = 343/4000 answer: = .08575 m

Solve for x in the following equation and write your answer in scientific notation: x = log623.

work: x = log23/log6 answer: C. 1.74995 x 10^0

Simply the following expression: (10^3)^2 • 10^9 / 10^4

work: (10^3)^2 • 10^9 / 10^4 (10^6) • 10^5 (10^6 • 10^5) answer: = *10^11*

Scientific notation - Exponents w base 10

• 10 to the power of 0 = 1 • 10 to the power of 1 = 10 • 10 to the power of 2 = 100 • 10 to the power of 3 = 1000 • 10 to the power of -1 = 0.1 - Utilizes exponents w base 10 in order to easily notate very large & very small #s - 3674 = 3.674 x 10 to the power of 3 - 451 = 4.51 x 10 to the power of 2 - First # is called the coefficient - Coefficients should always be between 1 & 10; there should be one non-zero # to the left of the decimal place - More examples • .00000145 = 1.45 x 10 to the power of -5 • .000000002293 = 2.293 x `10 to the power of -8 *don't worry about rounding to significant digits* • 2.13354 x 10 to the power of - 4 = 0.000213354

Practice problem : 320/16000

• 320/16000 • (3.20 x 10^2)(1.6000x10^4) • (3.2/1.6)(10^2/10^4) • 2.0 x 10^-2

Practice problems : 400 x 1500 (1st law of exponents)

• 400 x 1500 • (4.0 x 10^2)(1.500 x 10^3) • (4.0 x 1.5)(10^2 x 10^3) • 6.0 x 10(2+3) • 6.0 x 10^5

complex sound : aperiodic

• A complex sound that does NOT repeat itself regularly over time • Spectral energy is continuous, not distributed only at integer harmonics • Has a continuous spectrum - i.e., an INFINITE # of frequencies

Logarithms Finally Come In Handy! - what are they used for?

• A simple ratio still leads to a large range for easy plotting/calculations. • So to even further reduce the range, we will take the logarithm of the ratio. • This is called the Bel scale. Bel = log 10 (x/reference) One step more... • It was determined that using the Bel scale compressed the overall range of sound a little too much • Therefore, the decibel is used -- the Bel is multiplied by 10 dB IL = 10log(Ix/Ir) Ix = intensity of sound source Ir = reference intensity For purposes of this class, Ir will ALWAYS be 10^-12 W/m^2 • The formula referred to before is the way to calculate sound intensity level (referred to as dB IL) • Remember, we can classify the magnitude of sound according to intensity or pressure. • Recall that intensity is proportional to the square of pressure • Therefore, in order to display sound pressure level as decibels: •dB SPL = 10log(px/pr)^2 Recall the 3rd law of logarithms: - log a^b = b log a • So we simplify the formula: dB SPL = 10log( px/pr)^2 For purposes of this class, pr will ALWAYS be 2x10^-5 Pa - To calculate these ratios, we will use the following references: - For dB IL : 10^-12 W/m^2 - dB SPL : 2 x 10^-5 Pa • dB IL = 10log(x / [10^-12 W/m^2]) • dB SPL = 20log(x / [2*10^-5 Pa]) • The decibel scale is a derived scale from a ratio of two #s -- these are all RELATIVE sound level measurements, since we are comparing them all to a reference • The reference can change depending on what you want to compare your sound to, so it is quite important to specify! • Absolute measurements of sound magnitude would be in W/m^2 or Pa Also note... • Because the decibel is written as a RATIO, the units cancel each other out • So technically, the decibel is unitless • Need to specify whether you are referencing intensity or pressure

formula for acceleration

• Acceleration (a) - Change in velocity over time: Δc/Δt - Standard unit: m/s2

The goal: to use a scale that is more manageable when discussing sound intensity

• Also, it doesn't make much sense to speak about intensity levels lower than what is audible to the human ear • So, what if we tried just dividing everything by the reference intensity 10^-12 W/m ^2? • This would be a ratio scale (as opposed to a linear scale) - All of the y values will be divided by the same # in an effort to reduce the range.

Quantitive Measurements : exponents

• An exponent is a notation of how many times a # is multiplied by itself • 2 x 2 = 4 = 2^2 • a x a x a x a = a • X^0 = 1 • X^1 = X • X^-y = 1/(X^y) • Exponents can be multiplied & divided, but ONLY if the bases are equal • 10^1 x 10^6 • 82^5 / 82^7

3rd law of exponents

• An exponential term A^b is raised to some power c is equal to the base A is raised to the product of the two exponents b & c • (A^b)^c = A (bxc)

sound propagation : antinode

• Antinode - the location on a standing wave w/ maximal vibratory displacement • The # of nodes & antinodes depends on the frequency of the vibration & the length of the enclosing space

Formula for area

• Area (Ar) - The square of length: L x L = L2 - Standard unit: m^2

Resistance

• Resistance to force exists in the forms of friction or stiffness • The greater the resistance, the larger the force required to create acceleration or disturbance

Fourier's theorem : octaves

• Harmonic series can be divided into octaves - boundaries marked by harmonics that are a factor of 2n of the fundamental frequency - 1st octave = f0 * 2^1 - 2nd octave = f0 * 2^2 - 3rd octave = f0 * 2^3 - Nth octave = f0 * 2^n

How we relate dB SPL & dB IL.

• I = p^2/ p0c - Intensity is equal to pressure squared divided by the constant p0c = Zc (characteristic impedance of the medium) • I/Ir = (p^2/Zc)/(pr^2/Zcr) - We assume that the observed & reference sounds are measured in the same medium, & therefore have equal impedances - so they cancel each other out Therefore - for purposes of sound measurement, I/Ir = (p/pr)^2 Therefore, n dB IL = n dB SPL Just make sure you use the correct formulas & reference values to calculate them!

Decibels : adding sound pressure levels & adding intensity levels

• If two sounds are played simultaneously at 50 dB IL, what is the overall sound intensity level? • DO NOT simply add the decibel levels here - it is NOT 100 dB IL. Remember, these are derived values based on a ratio of absolute values. • In order to calculate summed sound levels, add the absolute intensity of each individual sound first

complex periodic sounds : line spectrum

• In a complex periodic sound, the energy in an amplitude spectrum appears at discrete frequencies relating to the fundamental frequency (finite #) • When this happens, we refer to this as a line spectrum - (As opposed to a continuous spectrum, where there are not discrete frequencies of energy)

Complex sound : periodic continuous

• In a complex periodic sound, the energy in an amplitude spectrum appears at discrete frequencies relating to the fundamental frequency (infinite #)

sound propagation : standing waves

• In enclosed or partially enclosed spaces, standing waves can be produced • Standing wave -- when a sound wave is continually reflected off of a surface in such a way that when the two encounter each other, they produce a pattern of minimum & maximum displacements that does not appear to propagate through space • standing waves occur when there is perfect constructive interference of an incident wave & its reflection in an enclosed space - Tube closed at both ends - Tube closed at one end, open at the other - Tube open at both ends • These spaces are considered to be enough enclosed that standing waves can occur • If sound is flowing through a tube, it is reflected regardless of whether the end is open or closed

Fourier's theorem

• Jean-Baptiste Joseph Fourier • Any complex sound can be decomposed into a series of sinusoidal waves • all sounds, no matter how complex, can be broken down into basic simple sine waves

Decibels : pressure vs intensity & how they relate to each other

• Magnitude of sound can be characterized in two ways: - Pressure (force/area) - Intensity (power/area) • Intensity & pressure are mathematically related - I = p^2/(p0c) • p0c is a constant - density of medium * speed of sound I p^2 (Intensity is proportional to pressure squared) • The softest sound intensity/pressure level that a human can hear: - 10^-12 watts/m^2 - 20 μPa, or 2 x 10^-5 Pa

Magnitude of sound

• Magnitude of sound can be characterized in two ways: - Pressure (force/area) - Intensity (power/area) • Power = the rate at which work is done - Primary unit for power = 1 Watt (W) - Primary unit for intensity = W/m sq. Magnitude of sound can be classified or measured as: - Intensity Level (IL) - Sound Pressure Level (SPL) Intensity & pressure are mathematically related I = p sq. /(p0C) p0c is a constant - density of medium * speed of sound I ∝ p2 (Intensity is proportional to pressure squared) • The softest sound intensity/pressure level that a human can hear: - 10^-12 watts/m^2 - 20 μPa, or 2 x 10^-5 Pa The pressure level of a sound that causes pain is about 10 million times larger than that This is a HUGE range of #s & extremely cumbersome to deal w/

complex sounds : amplitude & phase spectra fourier transform

• Mathematical algorithm that decomposes any waveform into its frequency or phase components • Provides us w/ the spectrum, another way to graphically display a simple or complex sound • Plotted in the frequency domain- Amplitude spectrum- Phase spectrum

basic properties of sound : amplitude

• Maximum & minimum displacement are also referred to as the peak amplitude, defined as -A to equilibrium, or equilibrium to +A (always a positive #) • Peak-to-peak amplitude - Twice the peak amplitude, or +A to -A (always a positive #)

sound propagation : Nodes

• Node - the location on a standing wave where there appears to be minimum vibratory displacement

Organization of auditory system

• Perceptual systems Outer ear, middle ear, inner ear/cochlea • Auditory Cortex Temporal lobe Auditory processing

basic properties of sound : period/frequency

• Period - the amount of time needed for the oscillation to complete one cycle - typically measured in seconds or milliseconds • Frequency - the rate at which the object vibrates; in other words, the # of vibrations per a specific unit of time- Typically measured in cycles per second, or Hertz (Hz) • f = 1/period; period = 1/f

basic properties of sound : phase

• Phase - the position of the object relative to resting state at any given point in time

formula for pressure

• Pressure - Force per unit area - Standard unit - N/m^2 (Pascal, or Pa) - p = F/A

Quantitive Measurements : scientific notation

• Scientific notation is a system that allows us to quantify very large or very small #s more easily • Scientific notation utilizes exponents w/ base 10 in order to easily notate very large & very small #s • 3674 = 3.674 x 10^3 • 451 = 4.51 x 10^2 • First # is called the coefficient • Coefficients should always be between 1 & 10; in other words, there should be one non-zero # to the left of the decimal place - More examples: • .0000145 = 1.45 x 10-^5 • .00000002293 = 2.293 x 10^-8

basic properties of sound : starting phase in phase/out of phase

• Starting phase - the initial position of the object prior to vibration • In-phase - same phase- Can have the same starting phase but different frequencies, but will not be in phase at all points in time • Out-of-phase - different starting phases, different instantaneous phases

sound propagation : sound shadow effect

• The amount of sound reflected also depends on the size of the object it encounters • If object is: - Smaller than the wavelength, then sound wave will bend around it & move past it w/out being affected -- diffraction - Much larger than wavelength, then sound will be mostly reflected - Reflection creates a shadow effect (an area of reduced sound energy directly behind the reflecting source)

sound propagation : inverse square law & how it applies to sound fields

• The farther away one is from a sound source, the softer the sound becomes • In other words, increased distance leads to decreased intensity/sound pressure level. • I = P / 4πr^2 • Doubling the distance --> 20 log (1/2) = -6 dB • You can extrapolate this formula such that you can calculate the amount of sound lost w/ any increase in distance: • e.g., traveling from 1 to 8 m: • 20 log (1/8) = -18.06 dB • Inverse square law only applies to a free sound field (sound field free of obstructions) • In actuality, most sound environments have boundaries which create the opportunity for reflection/diffraction/absorption • Reverberation time: The time needed for a sound to decrease by 60 dB

basic properties of sound : sine wave

• The formula is the graphical function of a sine wave - describing the simplest form of periodic oscillation • Energy at only one frequency • Also referred to as simple harmonic motion • Perceived as a pure tone

quantitive measurements : logarithms

• The logarithm of a # is the exponent by which the base has to be raised to produce that # Example: • y = a^x • x = logaY • In this case, the base term of the logarithm is a • To take the logarithm (or log) of a # is to solve for the exponent • logaA = 1 • loga1 = 0 • LogaA^x = x

Fourier's theorem : harmonic series

• The spectrum of a periodic complex sound may also contain energy at some or all harmonics - whole-# integers of the fundamental frequency • Referred to as a harmonic series

complex aperiodic sounds : transients or continuous

• Transient - a brief acoustic signal; a sound w/ a very short duration

formula for velocity

• Velocity (c) - Change in displacement over change in time: Δd/Δt - Standard unit: m/s

basic properties of sound : force vs. equilibrium

• Vibration is the movement that results when a force is exerted on an object • Object is displaced by a certain force needed to overcome its inertia • Elasticity is the property that allows the object to restore itself to its resting state (equilibrium)

sound propagation : wavelength & formula

• Wavelength - the distance between successive areas of condensation or rarefaction; the distance between peaks of a sound wave • Wavelength is dependent upon the frequency of the sound & the speed that sound travels through that particular medium c = fλ, or λ = c/f • f = frequency • c = speed of sound in the medium of question, in meters/sec • λ = wavelength (in meters)

Decibels : absolute pressure & absolute intensity formulas

• dB IL = 10log(x / [10^-12 W/m^2]) • dB SPL = 20log(x / [2*10^-5 Pa])

quantitive measurements : 2nd law of logarithms

• log (a/b) = log a - log b Example: Solve for x & display answer in scientific notation • 5 = log(10/x)

quantitive measurements : 3rd law of logarithms

• log a^b = b*log a Example: • log(10x/y)^3 = 3log(10x/y)