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XXXHearingSciFinal
XXXHearing Science Dr. Milner Final
| Question | Answer |
|---|---|
| Assessment of Auditory Sensitivity | method of assessment can influence results! |
| What kind of methods are used for assessment of auditory sensitivity? | psychophysical methods |
| Psychophysical methods are used for what? | assessing auditory sensitivity |
| What do psychophysical methods of auditory sensitivity link? | they link the physical properties of a stimulus to the perception and response to that stimulus |
| Before a listener responds to a stimulus what happens first | the stimulus is processed psychologically by the listener |
| What are the three main methods used for response when testing auditory sensitivity? | Method of LIMITS Method of ADJUSTMENT and Method of CONSTANT STIMULI |
| Method of Limits: | one parameter is changed to obtain threshold subject is asked to indicate if stimulus was heard and one approach is used (either ascending or descending) |
| With regard to Method of Limits one parameter is changed such as | Intensity |
| When one parameter is changed by the examiner such as intensity with regard to Method of Limits what is being obtained? | threshold |
| With regard to Method of Limits when the subject is asked to indicate whether the stimulus was heard or not how might this be indicated | raise hand or button push or some other behavioral response |
| What are the two approaches that relate to Method of Limits | ascending and descending |
| Method of Limits describe Descending Approach: | Sound starts off at an AUDIBLE LEVEL and then is decreased until it is inaudible… |
| With the descending approach the listener has | a clear mental representation of the sound but time above threshold is wasted. |
| What is the positive point of using descending approach to test hearing limits? | the listener has a clear mental representation of the sound because the sound starts off at an audible level. YIELDS LOWER THRESHOLDS TOO. |
| What is the negative point of using descending approach to test hearing limits? | time testing above threshold is wasted because the hearing test starts at an audible level and then the sound is decreased until it is inaudible. |
| Which has lower thresholds when testing hearing limits descending or ascending approach and why? | Descending yields a lower threshold by 3-4dB possibly due to listener having a clear mental representation of the sound they are trying to hear. |
| With regard to Method of Limits how is an ascending method of limits different from a descending one? | In ascending method of limits the sound starts out at a low level and is increased until it is audible to the listener. |
| What is the positive point of using ascending as a method of limits to test hearing? | if hearing is NORMAL this method is a relatively quick method – otherwise it can be time consuming… |
| In a hearing test blinking could be | a behavioral response indicating the stimulus was heard |
| In a hearing test with a very small child like a baby in the booth the cessation of sucking on a pacifier could be | a behavioral response indicating that the stimulus was heard. |
| How do you determine if a behavior is an indicator of a stimulus being heard? | the behavior has to be a consistent and clear response. |
| Visual Reinforcement Audiometry | child hears a sound looks at box box opens and there is a bear in there playing the drums – need two people test one has to keep child from just randomly staring at the box waiting for the bear to appear instead of responding to a sound stimulus |
| Visual Reinforcement Audiometry relates to | Conditioned Response by Skinner |
| The parameter that changes most often is | intensity |
| Why is intensity the parameter that changes most often | because it is useful to test for the softest intensity whereat a person can detect a stimulus |
| Descending: if the stimulus starts at 30dB what is the next dB level | 20dB – go down by 10dB and continue until the person stops responding. |
| We like using descending approach because of two reasons | the person has a clear mental representation of what they are listening for and they are REALLY LISTENING and the test yields lower thresholds. |
| With Ascending Method of Limits test you start off at a low level (zero) and work your way up. If there is hearing loss you may be | wasting quite a bit of time going up and up until you reach the person’s threshold… |
| If hearing is normal using the ascending method of limits is relatively | quick |
| If the person doesn’t respond at Zero in an ascending method of limits hearing exam the next dB level to test is | 15dB then 30dB then 45dB then to 60dB until they HEAR it. Keep going up in Ascending by increments of 15dB. |
| In an ascending method of limits hearing test you start at zero and keep going up by increments of | 15dB until the person can hear it. |
| If you have a person in the booth that is 75 years old and has a history of noise exposure and the person seemed to have trouble hearing you prior to the test | you might want to start at 50 and go up or down from there. |
| Ascending Method of Limits test is nice if the person has | normal hearing. |
| When you get an affirmative response on a Method of Limits hearing test you have to hone in on the | threshold |
| If the person in the booth gives you an affirmative response at 30dB and they raise their hand next you | go down by 10dB – if they didn’t hear it at 10dB then go UP by 5dB. You go down 10 and you go up 5. |
| The Down 10 Up 5 incremental adjustments in a hearing test is to utilize the clearing of the | auditory memory. We go UP from not hearing to hearing it. |
| It is important to present a stimulus in a hearing test in a | non-predictable pattern and do not provide any cues of when the stimulus was presented. |
| Varying the time between stimulus presentation is needed | Sometimes present close together or further apart so that the person cannot predict the signal and provide a false response. |
| Tell the person in the booth to raise their hand when they HEAR it and not when they ‘think’ they hear it | because otherwise you can have them overwork and get a false positive result. |
| To see a response to a hearing test | use peripheral vision or the audiometer light |
| If you go from 30 to 20 to 10 to 0 and they hear it at zero what do you do next | wait a while and re-present it at 0 – if they respond again at zero this is a valid response. |
| Do not test lower than zero because | no one cares if someone can hear lower than 0dB it is a ratio if there is no clinical value to doing something you shouldn’t be doing it. |
| Signal Detection Theory examines what? | Signal detection theory examines a listener’s ability to respond to the presence of a stimulus outlines the possible outcomes/subject responses and there are 4. |
| What are the 4 possible outcomes for Signal Detection Theory? | Hit Miss False Positive/Alarm and Correct Rejection |
| A psychophysical theory that examines a listener’s ability to respond to the presence of a stimulus with four possible outcomes/subject responses | Signal Detection Theory |
| What are the four possible outcomes to any test in which the listener must determine the presence or absence of a stimulus | Hit Miss False Positive/Alarm and Correct Rejection |
| Hit | A sound was presented and the listener indicates he/she heard it |
| Miss | A sound was presented and the listener indicates that she/he did not hear it |
| False Positive/Alarm | No sound was presented and the listener indicates that he/she heard it |
| Correct Rejection | No sound was presented and the listener indicates that he/she did not hear it |
| Outcomes #1 and #4 are | accurate responses |
| This theory is used extensively in medical testing with emphasis on reducing the false positive rate as much as possible | Signal Detection Theory |
| Method of Adjustment | is subject controlled |
| With Method of Adjustment | one parameter of the auditory stimulus is changed such as intensity by the listener in order to obtain threshold |
| With Method of Adjustment | The subject keeps the stimulus at a barely audible level by adjusting the correct button on a tracking audiometer The intensity variations are recorded and the tracking thresholds or record of sensitivity across frequencies are obtained |
| Method of Limit: | Examiner controlled! |
| Method of Adjustment | Subject/Participant controlled! |
| Which method is most often used in an experimental setting | Method of Adjustment |
| In Method of Adjustment in an experimental setting | patient becomes a participant |
| Method of Adjustment is Participant Controlled | the listener is the one changing the stimulus and adjusting the know to the point where the stimulus is ‘just audible’ |
| With Method of Adjustment even though it is participant controlled | you are still looking for thresholds while they turn the know down down down until it is just audible you use a tracking audiometer and you get tracking thresholds. |
| Method of Limits | testing ability to hear intensities but during that test you are also going to test frequencies. |
| During Method of Limits | you test ability to hear intensities and at varying frequencies and you do it from 250 – 8000 Hz in both ears. |
| During a Method of Limits exam we always start with 1000Hz | because that is a place where we anticipate success a place where most people can hear the stimulus. |
| During a method of limits exam | go from 1000 – 8000 then same ear again 1000 2000 etc to 8000 then test 500 and 250 last you have to get the threshold between + or – 5ddB to have it be valid results. |
| Auditory memory lingers there like | closing your eyes and you can still see something it lingers there. Same thing with hearing. So when you get an affirmative you go down 10 and up 5 to ‘erase’ the auditory memory. |
| Method of Constant Stimuli | Uses a technique called a two-alternative forced choice procedure |
| Method of limits or method of adjustment is used to approximate | hearing sensitivity for a certain stimulus. Several levels above and below this approximation are then selected |
| In Method of Constant Stimuli | The stimulus is then presented a certain amount of times such as 100 and the listener is cued to a time period when the stimulus will be presented The listener indicates “yes” or “no” to hearing the stimulus during this time period |
| In Method of Constant Stimuli | Results are plotted as the percentage of time each level of stimulus was detected in the correct time frame “threshold” is whatever definition the examiner chooses This is a dynamic measure that changes as parameters change |
| You have Choice A or Choice B | forced choice procedure you choose method of limits or method of adjustment to hone in on thresholds. |
| You present the stimulus a certain number of times | but in clinic we limit it or we’d be there forever. |
| Every time they hear the stimulus they hit a button or raise their hand and then out of 100 times we look at how many yeses to if they heard it and depending on the percentage set by examiner | 50% is threshold or 75% is threshold |
| In Method of Constant Stimuli we use | 50% because that is where the odds ‘shift’ |
| dBHL is only done in the | clinic |
| Subject Variables | A listener’s own predispositions to respond will influence test outcome |
| – Some people are more willing to respond than others | due to many reasons and this will influence thresholds |
| – The predisposition to respond a certain way is called a prepatory set | - which can be altered by examiner instructions |
| – Instructions can be altered throughout testing | based on observation of the subject’s behaviors and facial expressions |
| • Different listener variables like anxiety can influence results. Can relate to personality. | Can alter instructions if you perceive a hindrance. |
| • I am going to present it to them at 10 and over mike say yes that is the tone if they have a behavioral signal that indicates they likely heard it | and then go over your results by representing it several other to ensure it is valid data. |
| • Hearing sensitivity begins to decrease at around ages | 25-30 years of age |
| – Loss begins in the high frequencies | (4000 Hz and up) and then expands in frequency and degree throughout life |
| – Loss is greater in | men than women |
| – Loss due to aging is in many cases exacerbated by | noise exposure dietary differences life factors etc. |
| • Not everybody who ages gets a hearing loss it either | stays where it is or it gets worse. Outer hair cells high frequencies. |
| • Men more apt to be in environments where there is potential noise damage (professions.) (construction machinery etc.) | This is a generalization and ‘not true’ but there is some truth to it years ago only men were allowed into military. |
| • Loss due to aging is | presbycusis. |
| What is normal hearing? | • It is difficult to create a satisfactory definition |
| –• It is difficult to create a satisfactory definition | Hearing sensitivity varies across frequency: normal hearing and hearing loss must be defined differently at each frequency in dBSPL |
| • Extensive research in this area began in the 1930s at | Bell Telephone Laboratories |
| • Large amounts of young adults (18-25 years old) with no auditory pathology were tested and the median threshold for this group was obtained | This median became the “zero” decibel hearing level (0 dBHL) |
| • The frequencies that must be tested were determined by physiology | Equal distances along the BM separate points most responsive to frequencies one octave apart |
| – Thus hearing is tested at octave frequencies | between 250-8000 Hz |
| • Audiogram | record of thresholds at these frequencies |
| • 0 dBHL = audiometric zero. 0 dBHL is arbitrary | not a scientific measurement. |
| • We looked a physiology of the ear and determined where we need to hear the best | we found equal points along the basilar membrane and found the hearing range where the basilar membrane was |
| • We tested them at octaves they are doublings. An octave is a doubling in frequency. Half octaves between 2000 and 4000 is 3000. 3000 is the half octave and sometimes we test those. | To fit a hearing aid it is useful to test at half-octaves because at 3000 there is a lot of amplification. |
| Sound Localization | The ability to determine the location of a sound source in space: extracranial image |
| • The brain uses multiple pieces of information for localizing sound | This information must first be detected and then synthesized by the brain |
| Terms of Sound Localization: | Azimuth and Head Shadow Effect |
| – 1. Azimuth: | angle of incidence of the sound as it reaches the head measured in degrees |
| – 2. Head Shadow Effect: | the loss of intensity of a sound as the sound travels around the head |
| When a sound encounters an object longer than its wavelength | it is reflected or absorbed by the object |
| Head Shadow Effect | Effect is greatest for high frequencies |
| Minimum Audible Angle | : the smallest separation of angles of incidence that can be perceived |
| • Sounds are localized when the brain perceives | differences in the time of arrival and intensity of the sound arriving at each ear From peripheral and central level: |
| • Extracranial | : from outside in the world and brain uses multiple pieces of information for localizing sound. |
| • Azimuth: | an angle in degrees of incidence. 0 degrees azimuth directly in front directly behind = 180 degrees |
| • Counterclockwise or clockwise | depending on how you and the sound are oriented |
| • Head Shadow: sound travels around the head and you lose intensity because your head is in the way – | an object in space that causes damping in sound as it travels around it. |
| • Lower intensity on opposite side | No head shadow at 0 or 180. |
| • High frequency sounds lose their intensity because they have | a shorter wavelength. |
| • High frequency sounds have a shorter wavelength. | Long wavelength |
| • Low frequency sounds | wrap around things and can wrap around head. |
| • Shorter wavelength high frequency | just crash into things. |
| • Head shadow causes a | time difference cue. |
| • Minimal audible angle | the smallest separation of angles that can be perceived. |
| • Two people sitting close together asking a question | but it would be harder to detect who said it. |
| • Two sound sources close together | how close can they be and still be heard as two separate sources. |
| • It is the degree in between those two sources that help | identify the sounds as two sources. |
| • 2 sound sources close together in space | how close can they be to have it be a minimum audible angle. |
| • At some point they are so close they sound like ONE SOUND LOCATION. Detect 2 separate sound sources that are actually close together | – sounds like one source. |
| • When brain perceives a difference in intensity or angle | it helps with localization of the sound. |
| • If a sound source is at 0 or 180 degrees azimuth there is no difference in | intensity |
| • But at 0 degree azimuth it is in front of you | and you can see the sound source. |
| No difference from one ear to the other in 180 degrees because input comes in same intensity on both sides. | Same with 0 |
| • When the sound is coming at you head on | there is a slight difference in intensity as compared to 180 but the input is equal when you consider it from a left to right intensity perspective. |
| Intensity Differences If a sound source is directly in front of (0o azimuth) or behind (180o azimuth) the listener | there is no difference in the intensity of the sound arriving at each ear |
| – One ear is inevitably closer to | the sound source |
| – The head shadow effect means gain or loss of | intensity |
| • Sound is more intense on the side toward the sound source (near side) than on | the side away from the sound source (far side) |
| • When the azimuth of the sound is 90o the head shadow effect is greatest | but can be seen at smaller angles as well |
| – The result is an interaural intensity difference | (IID) |
| • Azimuth of the source can also effect ear canal resonance | seen when someone “cocks” the head to hear |
| • The IID is largest for tones 2000 and greater | therefore this is the cue used mostly for localization of high frequency sounds |
| • When you are not at 0 or 180 one ear is unavoidably closer to the sound source | even if only incrementally and brain can detect these variations. |
| • Intensity difference brain recognizes from head shadow is what the brain uses for localization and to | make the person’s head turn. |
| • Head shadow is a LOSS in intensity. When the azimuth of the sound is 45 degrees sound will still get to ear with diff in intensity but if 2 sounds present alternately at 45 degrees sound still comes in right to left only slightly different | but brain can still pick up the angle variation and look right or left depending on which side sound occurred. |
| • The IID is greatest for | 2000 Hz and greater and so the intensity cue is used most frequently to identify where the sound is coming from. |
| • High frequency sounds have shorter wavelengths and so therefore high frequencies generate a higher intensity difference from one ear to the other because there is no wrapping | only crashing and this lends to intensity cues. |
| Time Difference Cues | used primarily for the localization of lower frequencies |
| The distance the sound travels to the far ear is greater than to the near ear | when the azimuth if either 45 degrees or 90 degrees |
| What is the time difference for a 45 degree azimuth | near ear = .4 msec sooner |
| What is the time difference for a 90 degree azimuth | near ear .65 msec sooner |
| The brain uses time of arrival and phase differences ear to ear to | localize sound |
| Below 1800 Hz pure tone wavelength exceeds the 7'' difference between the ears resulting in a | phase difference of a sound at each ear |
| ITD | Interauraltime difference |
| The ITD and phase differene of the sound between the ears can be enhanced by | head movements |
| Minimal Audible Angle | the smallest angular separation that can be perceived |
| MAA depends on | the azimuth of the sound source |
| A much smaller MAA is achieved when the azimuth is | 0 degrees |
| When the azimuth is 90 degrees 180 degrees or 270 degrees the sound source must be a greater distance apart in order to perceive the sounds as | two separate sounds. |
| Most sounds we encounter in everyday life are complex rather than | pure tones |
| Because most sounds we encounter in life are complex rather than pure tones we use these siimultaneously to localize sounds | IIDs and ITDs |
| IID | interaural intensity difference |
| ITD | interaural time difference |
| The auditory system is part of a complex system of perception that includes these systems | visual tactile olfactory and cognitive systems |
| Which four systems comprise the complex system of which the auditory system is a part | visual tactile olfactory and cognitive systems |
| Both of these can be changed by moving the head | IID and ITD |
| Determining the sound source under headphones requires use of | an intracranial image |
| If you present identical pure tones under headphones | listener perceives the sound as in the middle of the head |
| If you increase the sound of a tone in the right ear relative to the left | listener perceives sound as moving to the right ear. |
| When the difference in intensity of sound at each ear reaches 30 - 40 dB | the listener only perceives the sound in the ear where it is being presented with the greatest intensity. |
| Very small differences (approximately 10 microseconds) in the time of arrival at each ear under headphones can result in te perception of | the sound reaching one ear sooner than the other. |
| How does the brain localize low frequency sounds? | Below 2,000 Hz, the brain uses a time difference cue for localization. |
| If a sound is at 90 degrees azimuth to the right of you the sound arrives at which ear sooner | it arrives at the right ear sooner than the left ear. |
| Time difference is greatest at which 2 degrees | 90 degree and 45 degrees |
| Perception localization and comprehension all take place | very fast |
| 45 degree azimuth sound arrives at near ear how much faster on average than far ear? | .4 seconds faster |
| 90 degree asimuth sound arrives at near ear how much faster on average than far ear? | .65 seconds faster |
| Brain looks for differences in | time of arrival at each ear and phase difference at each ear |
| Average distance between ears is 7 inches | so we know what the wavelength is for sounds below 1800 |
| for 1800 Hz and below we use ITD and phase difference for | localization cues |
| For 1900 Hz we use time and intensity differences for | localization of sounc |
| MAA is smaller when | you have an azimuth of 0 degrees |
| As most sounds are complex we are using IIDs and ITDs all time, | to localize sound |
| We are not usually localizing by auditory stimuli alone, | we use other senses such as visual, tactile, olfactory and cognitive systems too. |
| lateralization under headphones | Intracranial image |
| Localization in sound field | Extracranial image |
| Differential Sensitivity | how much is the smallest change in a parameter of a stimulus such as frequency or intensity that must be made in order to be recognized by a listener |
| Differential Sensitivity | also known as Difference Limen DL |
| Difference Limen | DL- the differential sensitivity – smallest detectable change in a parameter of a stimulus |
| DL or Difference Limen is also known as JND | just noticeable difference |
| JND = | DL |
| Detection of small changes in stimulus magnitude is a crucial auditory skill for | sound localization and speech understanding |
| Most studies of differential sensitivity DL or JND use two tones | the standard tone and a comparison tone |
| The standard tone and the comparison tone are tones that differ just slightly in | frequency intensity or duration |
| What are the three parameters that may be changed to detect JND or DL | frequency |
| Why is it important to detect small differences in intensity frequency and duration | these differences are used in speech sounds |
| When you have two phonemes you need to be able to perceive the formants in one vowel as different from formants in other vowels in order to | perceive them as two different sounds |
| If you couldn’t tell the difference between /s/ and /sh/ it could lead to communication breakdown in speech understanding and sound localization | so JND and DL are important. |
| You need differential sensitivity for all parameters in order to | understand speech. |
| Weber found that the difference between 2 objects that could be detected was proportional to | the value of the smaller object. |
| The amount of change in magnitude necessary for the change to be noticeable depends on the | initial magnitude of the stimulus |
| If there were 10 items in a basket and you changed one | the change would be noticed |
| If there were 100 items in a basket | you would need to change 10 in order for the change to be noticed. |
| 17th Century Fechner and Weber’s method of looking at differential sensitivity as a proportional change relative to initial magnitude of a stimulus | S/S = constant(k) |
| In S/S = constant(k) what is K | K = constant |
| In S/S = constant(k) what is S | S = stimulus |
| In S/S = constant(k) what is | = change |
| In S/S = constant(k) what is this known as | Weber’s Law or the Weber/Fechner law |
| In S/S = constant(k) Weber’s Law or Weber/Fechner Law holds best at | mid frequencies NOT low ones (750 Hz - 2000 Hz) |
| Descrimination task | you decide if two tones are the same or different |
| Differential sensitivity can be detected as a proportional change relative to | the initial magnitude of stimulus |
| Delta S | change in the stimulus divided by the stimulus |
| Delta S | used to determine what is the smallest change in frequency intensity or duration that we can detect. |
| The smallest change in the frequency intensity or duration of a stimulus that we can detect depends on | the initial magnitude of the intensity |
| DL or JND a.k.a the difference limen as it applies to frequency is known as | DLF (subscript F) |
| DLsubscriptF is | the smallest difference in frequency that can be judged by the listener. |
| DLF is a frequency discrimination task using same/different of | standard tone and comparison tone presented at the same intensity for the same duration |
| DLF becomes smaller as the stimulus intensity | increases |
| DLF becomes larger as the stimulus frequency | increases especially above 1kHz |
| Most listeners are relatively insensitive to frequency changes at low | LOUDNESS levels. |
| Overall sensitivity to some frequencies is better than others | DLF values remain constant at 500 Hz – 4000 Hz with best sensitivity at 1000 Hz – 2000 Hz. |
| Best sensitivity | 1000 Hz – 2000 Hz |
| At low frequencies | the DLF can be as small as 1Hz. |
| DLF is the smallest difference in frequency that can be detected by a listener when presented | 100 times |
| With louder sounds we can detect | small differences in frequencies |
| As stimulus frequency increases | the DLF gets larger |
| You want a small | difference limen |
| With a louder or more intense sound our ability to distinguish frequency | improves |
| Low loudness is | low intensity |
| Most listeners are relatively insensitive to frequency changes as | low intensity levels |
| There are two assessment methods for DLsubscriptI | standard same/different comparisons and present a steady tone and vary its intensity |
| DLI is difference limen for | intensity |
| Intensity discrimination | DL subscript I DLI |
| DLI discrimination tasks | standard same/different comparisons and present a steady tone and vary its intensity |
| Standard Same/Different discrimination task uses | a standard tone and comparison tone of the same frequency |
| Steady Tone varied in intensity | present a steady tone and occasionally vary its intensity for brief periods and see if the listener can detect the change |
| Research has show that the auditory system is sensitive to changes of | .5 to 1.0 dB across a broad range of frequencies |
| Logarithms are used for | measuring sound |
| A progressively larger change in sound pressure is required to increase SPL at higher pressures than at lower pressures | a logarithmic concept |
| The change in sound pressure required to increase SPL from 80 to 81 is 1000 times greater than to increase it from 20 to 21 | log function. |
| You can detect a 1dB change in 80 dBSPL signal | but not in a 20 dBSPL signal |
| You can detect a 1dB change in 80 dBSPL signal but not in a 20 dBSPL signal due to | the larger change in pressure required at 80. IT IS NOT THE SAME PRESSURE CHANGE. |
| Temporal Discrimination | DLsubscriptT |
| DLT is a measure of | temporal discrimination |
| In DLT the subject listens to two stimuli | one of fixed duration and loudness level and a comparison tone of different duration and equal loudness level. |
| In DLT the subject listens to two tones of different duration and determines | which was longest. |
| DLT is the smallest difference in duration that can be deteremined between the standard tone and comparison tone that results in correct judgements with what percentage of accuracy | 75% accuracy. |
| Temporal Resolution | = Temporal Auditory Ability |
| Temporal Auditory Ability = | Temporal Resolution |
| The shortest time necessary for discriminating between signals = | Temporal Resolution |
| Gap Detection Threshold = | the shortest interruption of a signal that can be detected |
| To determine Gap Detection Threshold | listener is presented with a very brief gap between stimuli that is varied in time and indicates if they hear one or two tones as the durations shortens. |
| Generally sensitivity to time differences improves as | the length of the stimulus increases. |
| Temporal Resolution is the | shortest gap after which two tones can be perceived as separate stimuli |
| Gap detection is best in mid frequencies | 750 Hz – 2000 Hz |
| Masking is when | the threshold of one sound (the signal) is raised by the presentation of another sound (the masker) in order to preclude the listener from hearing the signal in that ear. |
| Masking is keeping one ear busy | so that it cannot participate in the test and the true abilities of the test ear are measured. |
| There is no universally accepted signal that serves as a | masker |
| Maskers can be | tones or noise depends on what needs to be masked |
| Threshold shift | hearing is 20dB without water running in the background – water goes on and the hearing threshold increases to 50 dB creating a 30 dB shift meaning the water produced 30 dB of masking. |
| The test ear is the ear that is referred to as | masked |
| You put the masking into the good ear | you put the noise in the good ear to keep it busy |
| When you talk about the results you say that you tested the left ear for the test and talk about Left Masked Air Conduction. | and talk about Left Masked Air Conduction. |
| Can do masking by both | air and bone conduction |
| Bone conduction results are always non-ear specific because | you can’t vibrate only one side of the skull. |
| Music masks the speech at a party unless you want to hear the music then the speech is the problem | signal and masker can change. |
| Masking requires a narrow band noise | use a filter to get rid of select frequencies. |
| A narrow band noise is used for | masking |
| The ear that gets the tone is the | masked ear |
| The results are ‘left masked’ if you are | testing the left ear and putting noise in the right ear |
| Listen to music with a quiet fan in the background | no interference of the fan noise with the music |
| Raise the level of the fan while holding the level of the music constant | eventually the fan will interfere with the music |
| Distraction of the fan leads to | masking of some of the weaker musical notes leading to the music becoming inaudible. |
| Present a pure tone at threshold and present noise at low level | often hear both noise and tone |
| Gradually increase the level of the noise while holding the tone constant | and eventually all the listener perceives is noise |
| The lowest level of NOISE that renders the tone inaudible = | 0dB effective masking level or kneepoint |
| Level of the tone would have to be increased in order to make it audible of noise is at | kneepoint |
| Straight lines that meet at a bend | can introduce a noise with no effect on the one until a certain point no change in the threshold of a tone. |
| At some point the SPL of the noise reaches some critical value and | the threshold of the tone will shift |
| At levels above the knee increases in noise will produce equivalent increases in threshold 1:1 relationship between noise and the masking effect | each dB increase in noise produces an equivalent shift in the threshold of the tone |
| Kneepoint | that level of noise above which any additional noise increase will produce an equivalent threshold shift. |
| A noise that is 10dB of effective masking will fall 10dB avove the kneepoint and produce a 10dB threshold shift | in the tone |
| Threshold shift | the numerical difference in dB between a threshold in quiet and a threshold in the presence of a masker. |
| The most efficient masker is the signal that | provides the most masking for the least amount of energy |
| The most logical masker of a pure tone is another pure tone | but then the listener cannot distinguish between the two tones |
| If with two pure tones the masker is of a different frequency this is called | beats sensation |
| The frequency of the masker should be close to that of the signal | but not too close |
| When the level of the masker tone is 60 dB and above | its masking effect is much greater above the masker frequency than below it. |
| The masking effect spreads rapidly upward to higher frequencies | as the intensity level of the masker is reached. |
| Upward Spread of Masking | the masking effect spreads rapidly upward to higher frequencies as the intensity level of the masker is reached. |
| Narrow Band Noise | NBN |
| Narrow band noise | noise within a certain frequency range |
| The Narrow Band Noise is shaped through the use of a band-pass filter with a | high and low cut off frequency |
| Frequencies inside of a narrow band noise are attenuated gradually | as frequency becomes more remote from the cut off |
| The gradual attenuation in a narrow band pass noise is called | roll off |
| Roll off is measured in | dB/octave |
| Using NBN to mask pure tones uses the concept of a | critical band |
| The concept of a critical band | is that there is a range of frequencies around the signal or test frequency that contribute most to masking that frequency. |
| Only a narrow band of frequencies around a pure tone | contribute to the masking of that tone |
| Frequencies outside the critical band do not | Frequencies outside the critical band do not contribute to masking they only add on to the overall noise level. |
| When a tone is barely masked by noise | the energy in the critical band is equal to the energy of the tone. |
| NBN reaches the 0 dB effective masking level at a lower SPL than white noise | making it a more efficient masker. |
| NBN has energy distributed equally over a narrow restricted frequency range | white noise has energy distributed over a broad range. |
| NBN is the preferred masker for | pure tones |
| If the noise energy within the critical band is less than that of the energy level of the tone being masked | then there is no threshold shift. |
| The 0 dB effective masking point (or kneepoint) of the noise is where the energy falling within the critical band first equals | that of the tone. |
| From the 0 dB effective masking level on each dB increase in noise within the critical band will produce | an equivalent increase in the pure tone threshold |
| NBN works well for masking tones but not for speech | for masking speech a broader range of frequencies is needed. |
| Masking Special Cases | simultaneous masking forward masking backward masking |
| Simultaneous masking | the scenario where the masker and maskee are presented together |
| When the masker and the maskee are presented together as in simultaneous masking the time between the two must be brief | less than 50 msec |
| Forward masking | the masker is presented and ended just before the signal is presented |
| Backward masking | when the signal is presented and terminated just before the masker is presented |
| Masking level difference | until now masking has been discussed as presenting the noise and tone in the same ear |
| To find the 0 dB effective masking in that ear | the level of the tone is adjusted until the tone is just inaudible (ipsilateral masking) |
| Take a tone below 500 Hz and add noise to the other ear (contralateral masking) and the tone becomes | inaudible in the test ear without changing the signal or noise in that ear. |
| Add stimulus tone to the other ear | now both ears have tone and noise (masker) and the tone is not heard by either ear. |
| The phase of the signal or masker must be changed by 180 degrees in either ear | for the stimulus to become audible again. |
| The MLD (masking level difference) is determined by | the amount of reduction in masking provided by a particular condition referenced to the condition that provides maximum masking. |
| This condition is almost always when the signal and masker are | in phase binaurally. (SoNo) |
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