Audiology

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Magnitude estimation: An observer assigns numbers to a variable stimulus according to its apparent intensity, often after being presented with a standard stimulus and told what number to assign to it.
absolute threshold: Lowest level of stimulation that a person can detect.
malleus: Attaches to the tympanic membrane and the incus. Also attaches to the tensor tympani muscle which has the startle reflex. Composed of the head, the manubrium, the neck, the lateral process, and the anterior process.
audiometer: Basic screening for hearing acuity, fast simple test to detect problems, uses tones at different frequencies patient raises hand or finger when hears tone, light indicates sound, client should respond at the same time.
The critical band: Only those frequency components within a narrow band will mask a given tone; also refers to the specific area on the basilar membrane that goes into vibration in response to an incoming sine wave. Average length of the critical band is ~1mm.
Pascal: mks unit of pressure. 1 pascal = 1newton / meter squared.
method of limits: The experimenter presents stimuli in alternating ascending and descending order.
Semicircular Canals: Structure in inner ear that is responcible for balance.
Bandwidth: The maximum amount of data that can travel over a given data transmission channel in a given amount of time
compression response of the inner ear: Vibration in the skull vibrates the walls of the cochlea creating sound in the cochlea thus triggering the traveling wave. Sometimes called the distortion mechanism. This is the greatest contribution to the bone conduction of sound to the cochlea.
recruitment: Abnormal growth in loudness per increase in intensity;usually experienced by those with cochlear problems.
sone scale: dbSL; standard is 1000hz, 40dbSL. first standard stimulus is presented, then a comparison stimulus. If the comparison stimulus is twice as loud as the standard, then it's 2 sones. enables us to relate loudness to intensity. SL stands for sensation level = # of decibles above threshold for that sound. For example, if someone's absolute threshold at 1000 hz = 4dbSPL the answer would be 44dbSPL; you would add 40dB to 4dB SPL to equal 44dB SPL.
Interaural timing difference: The interaural time difference (or ITD) when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localisation of sounds, as it provides a cue to the direction or angle of the sound source from the head.
White Noise: Aperiodic waveform that consists of all frequencies; a broadband noise.
Interaural Intensity Diffference: Interaural level differences (ILDs), sometimes called interaural intensity differences (IID), are differences of the soundpressure level arriving at the two ears; and are important cues that humans and animals use to localise higher frequency sounds.
Period: 1 / number of Hz, e.g. 1 / 250Hz = 0.004 sec.
Basilar Membrane: Separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani. The motion of the basilar membrane is generally described as a traveling wave. The parameters of the membrane at a given point along its length determine its characteristic frequency (CF), the frequency at which it is most sensitive to sound vibrations. The Basilar membrane is widest and least taut at the apex of the cochlea, and narrowest and most taut at the base. High-frequency sounds localize near the base of the cochlea (near the round and oval windows), while low-frequency sounds localize near the apex. The basilar membrane places the hair cells in a position where they are adjacent to both the endolymph and the perilymph. The basilar membrane has the function of frequency dispersion of incoming sound waves. In brief, the membrane is tapered and it is stiffer at one end than at the other. The dispersion of fluid waves causes sound input of a certain frequency to vibrate some locations of the membrane more than other locations (Georg von Békésy). This is the place theory.
Periodic Waveform: A periodic waveform is one which repeats the exact same shape again and again. It doesn't change, so both its shape and its harmonic content stay the same for the waveform's whole duration.
bone conduction vibrator: Placed on the mastoid process of the pinna. It plugs into the audiometer and vibrates the entire skull. When you stimulate via bone conduction (though the motion of the ossicles) the cochlea, you create the same traveling wave as you do air conduction which vibrates the entire cochlea. The effect on hair cells is the same.
Acoustic Reflex: The contraction of the stapedius muscle in response to loud sounds and is a bilateral effect - stapedius muscles in both ears will contract. The amount of contraction relates to the decibel level. Graded response. When the stapedius muscle contracts, it stiffens the ossicular chain, thus reducing sound transmission to the cochlea (only at low frequencies below 200 Hz).
Occlusion effect: If you block your ear with a finger or an earplug, the sound gets louder because the sound happening in the ear canal has less room, thus creating more pressure, leading to ludness. Also called the osseotympanic mechanism.
binaural hearing: Binaural literally means "having or relating to two ears." Along with frequency cues, lets humans and other animals determine direction of origin of sounds.
Case of the missing fundamental: In the very low frequencies, there is no acoustic energy near the fundamental frequency (100 Hz).
Reticular Lamina: Extracellular material containing fine collagenous or reticular fibres secreted by connective tissue cells abutting the basal lamina.
Stevens' Power Law: A proposed relationship between the magnitude of a physical stimulus and its perceived intensity or strength; that the magnitude of a perception is equal to a power (exponent) of the magnitude of the stimulus.
aperiodic waveform: A waveform that does not have a repeating pattern such as a dog bark.
bone-air gaps: If these are occuring, calibration of the audiometer could be off or the bone vibrator could be placed improperly placed on the mastoid. They sometimes slip.
Magnitude production: An observer adjusts a variable stimulus until it stands in some prescribed relation of magnitude to a standard stimulus, as when an observer adjusts a sound stimulus until it appears equal in loudness, twice as loud, or half as loud as a comparison sound. Also called the production method.
Internal Auditory Meatus: Origin is inside the cranial cavity, near the center of the posterior surface of the temporal bone. It's about 1 cm. It does not transmit sound waves. It instead transmits the facial, the cochlear nerve, and both branches of the vestibular nerve.
acousic radiations mechanism: You're having the whole skull vibrate so the walls of the ear canal vibrate, thus sound radiates through the ear canal which hits the tympanic membrane, continuing on the the ossicles, etc.
Stereocilia: The top of the hair cells (stereocilia) transform the mechanical energy of sound pressure into electrical signals for the hair cells, which ultimately leads to an excitation of the auditory nerve. When the stapes causes sound waves in the endolymphatic fluid in the cochlea, the stereocilia are deflected by shear force, which results in the mentioned electrical signal for the hair cell. The Organ of Corti sways and the stereocilia tilt. Tilting movements of the stereocilia affects the tension on the filaments in the tip link which opens and closes the gated ion channels (the gating spring effect). When cilia are deflected away from the spiral limbus the hair cell is depolarized.
Sensory-neural loss: Also referred to as a cochlear loss. Involves either the auditory nerve / pathway or the cochlea (including hair cells). 90% of the time it is cochlear.
Mel Scale: Standard stimulus is always presented at 40SL.
Decibel: The formula for decibels given two sound pressures: 20log10 P1/P0. Each time sound pressure is doubled, there is a 6dB increase in its level. If we reduce the pressure to half, there will be a 6dB decrease. Combining 2 sounds with the exact same waveforems will double the sound pressure - the level of the combined sounds will be 6dB greater than either sound alone. Two waveforms that are not exactly the same there will be an increase of only 3 dB.
Beat: Oscillation of a wave amplitude that occurs as a result of a superposition of two sound waves having nearly identical frequencies.
spectrum: Amplitude is on the Y-axis and frequency is on the X-axis; vertical line.
Masking: The audibility of one sound is reduced by the presence of another sound, e.g. passing out tests while the rest of the class is talking. A process by which the threshold of audibility of one sound is raised by the presence of another sound.
Upward masking: Lower frequency maskers are more effective than high frequency maskers.
bone conduction: Transmission of sound through the bone. When you hear yourself talking, it's bone conduction. The symbols for bone conduction: left = > and right = <. It is assumed that we're bypassing the middle ear and going directly to the cochlea.
perilymph: Na>K/ space betwen membrane and temporal bone. The cell bodies of the cochlear hair cells are immersed in perilymph.
Ratio Scale: Differences between values can be quantified in absolute terms and a fixed zero point is defined. Equal differences between scores represent equal differences in the attribute being measured, and a zero score represents complete absence of the attribute. It is only when measurement reaches the level of a ratio scale that it is meaningful to describe a score as twice the value of another score, for example.
Outer Hair Cells: Auditory receptor cells that have a many-to-one ratio with auditory nerve fibers, the receptor potential triggers active vibrations of the cell body. Enable hearing sophisticated speech and music. Cochlear hair cells have a resting potential of +80mV.
incus: Composed of the head (the articulation with the malleus), the lenticular process at the bottom, the short process at the top (lateral to the head), and the long process.
Sine Wave (aka Sinusoid): A form of repeating wave that changes the field through which electric and magnetic properties pass.
Gating Spring Mechanism: Hair cells use something very much like a spring that opens their channels when the cilia bend, without the need for a time-consuming chemical exchange.
Partition Scales: Subject is presented with a range of intensities or frequencies and is asked to divide (partition) this range into equally spaced catagories on the basis of how she percieves them.
direct scaling: Any method of scaling such as magnitude estimation or cross-modal matching in which an observer specifically estimates the magnitude of the variable stimulus.
absolute threshold: The lowest level of stimulation a person can detect.
Intermodulation distortion product: Intermodulation or intermodulation distortion (IMD), is the result of two or more signals of different frequencies being mixed together, sum and difference frequencies are also produced in addition to the harmonics. This can be shown mathematically to be the result of a multiplication process between the two original frequencies and hence the two new frequencies are called products. If the two original frequencies are f1, f2 and the highest frequency is f2, then we can expect two other components (or products) of (f1+f2) and (f2-f1). However, it doesn't stop there. Since there are harmonics of f1 and f2, then there will be sum and difference products between all of the harmonics and the fundamentals and between each other. These are the intermodulation products which are frequency components distinct from the harmonic components discussed in the previous paragraph. Of course, if there are more than two fundamental frequencies, then the multitude of products is compounded further.
Wavelength: wavelength = speed / frequency, e.g. wavelength = 341m/sec. / 200Hz = 1.705m/secHz.
External Auditory Meatus: The ear canal (external auditory meatus), is a tube running from the outer ear to the middle ear. The human ear canal extends from the pinna to the eardrum. Includes the concha which forms part of the entrance and is important in the manufacturing of cerumen.
bracketing: Increasing and decreasing the level alternately until a change point is reached; employed in the method of limits.
Reissner's membrane: Forms an ionic barier between perilymph and endolymph.
Psychometric function: Describes the relationship between a parameter of a physical stimulus and the responses of a person who has to decide about a certain aspect of that stimulus.
Cross-modality matches: An observer matches the apparent intensities of stimuli across two sensory modalities, as when an observer adjusts the brightness of a light to indicate the loudness of a variable stimulus sound.
Atmospheric Pressure: Pressure of the air at sea level.
head shadow: A head shadow is a region of reduced amplitude of a sound because it is obstructed by the head. Sound may have to travel though and around the head in order to reach an ear. The obstruction caused by the head can account for a significant attenuation (reduced amplitude) of overall intensity as well as cause a filtering effect. The filtering effects of head shadowing cause one to have perception problems with linear distance and direction of a sound source. frequencies above around 1.3kHz are reflected, producing a head shadow; frequencies below 1.3kHz aren't reflected and no head shadow is created. As a rule of thumb, the sound is reflected if the wavelength is shorter than the diameter of the object.
pitch: The preceived highness or lowness of a sound, depending on the frequency of sound waves; Standard Stimulus: 1Khz at 40dbSL and 1000 mels. Then subject is presented with a comparison stimulus. If it's twice the pitch of the standard it is 2000 mels, etc.
Bekesy Tracking: A type of method of adjustment. The listener pushes a button as long as he can hear the tone and lets go when he stops hearing the tone, so the level goes up and down around threshold. The tone changes during the course of the test so that thresholds can be estimated at many frequencies.
supra-aural ear phones: Go over the pinna. Use air conduction.
Aural Harmonics: When a sine tone or complex tone is played loudly enough, additional harmonics will be heard that are not present in the original tone. These added tones, being frequency multiples of the original tone, are called aural harmonics. Like combination tones, aural harmonics are a form of distortion caused by non-linear processing of the inner ear.
Stapes: Articulates with the lenticular process of the incus. Composed of two crura (Anterior crus and Posterior crus), the head, and the footplate that covers the oval window which is an opening into the inner ear cavity. Attaches to the stapedius muscle which contacts in response to high intensity sound stimuli.
Audiogram: A grah depicting the threshold of audibility (in decibels) as a function of different frequencies, a graphical representation of a person's auditory sensitivity to sound. Circles mean I'm testing the right ear.
Complex Waveform: Combining two or more sinusoids of different frequencies.
Differential threshold: The point of sensitivity at which the least amount of change in a stimulus gives rise to a change in sensation. AKA just noticible difference (JND).
loudness: The precption of the amplitude of a sound wave.
Masked Threshold: Equal to masked threshold - threshold in quiet.
Traveling wave: In the auditory system, vibration of the basilar membrane in which the peak of the vibration travels from the base of the membrane to its apex for low frequency sounds.
Modulus: Standard tone.
air conduction: The pathway of sounds that includes the oter ear, middle ear, inner ear, and the structures beyond. When you hear your own voice oon a recording, you are using air conduction. The entire ear is represented - the outer ear, the inner ear, and the middle ear. Conductie hearing loss - something is wrong with the middle ear or the outer ear.
db SPL / dB unit rules: Logarithmic measure of the rms sound pressure of a sound relative to a reference value. It is measured in decibel (dB)., When the reference pressure of a sound is 20 microPa (0.00002); dB SPL stands for Sound Pressure Level. When we add or subtract a dB SPL and a dB value gives you a unit of dB SPL. e.g. 30dB SPL tone + 15 dB = 45dB SPL. dB SPL + dB SPL = units in dB. e.g. 120 dB SPL - 5dB SPL = 115 dB.
method of adjustment: The experimenter adjusts the stimulus continuously until the participant can perceive it.
Tectorial membrane: Covering Organ of Corti and attached to the limbus laminae spiralis close to the inner edge of the vestibular membrane. Along its lower surface, opposite the inner hair cells, is a clear band, named Hensen's stripe, due to the intercrossing of its fibers. Partially covers the hair cells in Organ of Corti and vibrate when fluid sound waves hit it. The general transverse direction of the fibers inclines from the radius of the cochlea toward the apex and are coupled to the cilia of outer hair cells.
bone conduction threshold: A good diagonstic test for bone conduction or air conduction problems. Bone conduction vibrators don't tend to go above 4000 Hz.
endolymph: High K+/low Na+/ inside membranous labyrinth. The cilia of the cochlear hair cells are immersed in endolymph. Banana island.
Conductive hearing loss: Hearing impairment caused by interference with sound or vibratory energy in the external canal; middle ear, or ossicles. Possible due to a blockage of cerumen. Air-bone gap is the gap between the air conduction threshold and bone conduction threshold.
Dynamic Range: The difference in volume between the loudest and quietest sounds of a source.
Acoustic reflex: Stapedius' contraction due to intense sounds. Minimizes the amount of sound that reaches the inner ear. Low frequencies (mainly those below 2000 Hz) are affected by the acoustic reflex.
Intensity: 10log10 I1/I0. Doubling intensity increases the sound by 3 dB. The unit of intensity is Watts / m squared.
Heschl's gyrus: The principle auditory area of the cerebral cortex.
Tip Links: Threadlike fibres that run along tips of stereocilia and are key to AP's; when sound causes stereocilia to sway tension on tip links pop open ion channels.
Air-bone gaps: [Must know how to measure / read them and the significance of them.] The results of your air-conduction hearing tests and the results of your bone-conduction hearing tests don't match each other because your air-conduction tests gave much poorer results than your bone-conduction tests. The difference (or gap) between these two lines plotted on your audiogram is the air [conduction] - bone [conduction] gap or air- bone gap for short. For example, if your audiogram showed an air- conduction hearing loss of 70 dB while your bone-conduction test results only showed a 40 dB hearing loss for a given test frequency, then the difference between them in this case would be an air-bone gap of 30 dB (70 - 40 = 30). A gap of 10dB or less is not clinically significant.
inertial or ossicular lag mechanism: Relative movement between the ossicles and the temporal bone.
speed of sound: 341 m/sec.
Inner Hair Cells: Auditory receptor cells that have a one-to-one ratio with auditory nerve fibers.
Eustachian tube: Connects the middle ear with the nasopharynx and allows the passage of air..
sensation level: Number of db above threshold (always 40db above threshold).
dB SPL: Used when the reference pressure of a sound is 20 microPa (0.00002); dB SPL stands for Sound Pressure Level.
Mixed hearing loss: When there is a combination of conductive hearing loss and sensory-neural hearing loss.

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