SLHS 305 Final

Loudness recruitment

A rapid growth of loudness as the level of tone is increased -abnormal sensitivity to loudness -damaged auditory system not refined by cochlea -reduced dynamic range -ULL rarely increases, most likely consistent Two Hypotheses: 1)Reduced frequency selectivity along the basilar membrane may cause an increase in loudness growth (cochlear damage) 2) Destruction of OHC's would result in a loss in the amplification of low level signals while the perception of the higher level sounds remains unchanged damage: takes higher level sounds to stimulate hair cells, higher thresholds

The weighting scale that is most similar to human hearing (i.e., MAF) is the

A scale

Narrow banded noise

Centered around the frequency

Temporal Masking

Changing the temporal gap (amount of time gap) until you only hear one tone Backward masking - signal precedes the masker in time /beep/ => /shh/ 50 ms after Forward masking - signal follows the masker /shh/ => /beep/ 75 - 100 ms before beep ^ always a wideband noise

MAP-Sennheiser

Circum-aural earphones, around ear up to 20,000 Hz. -ultra high freq. headphones

Other Psychophysical Factors

Difference limens for frequency are larger for individuals with hearing loss Dynamic range is smaller -frequency, level and timing all get larger or require bigger difference -just noticeable difference

Binaural masking

Monotic - stimuli presented to only one ear Diotic - identical stimuli presented to both ears Dichotic - different stimuli to the two ears All related to the MLD You can have lower/better thresholds in dichotic than monotic and diotic in dichotic, threshold improves by 15 dB

Permanent threshold shift

Symptoms: acute, temporary, chronic, constant Tinnitus: no one knows the cause or how we can fix it -ringing or buzzing in ear, something permanently wrong -can cause psychological problems -possibly something to do with the neural pathway -it is possible that some mechanical energy may be reflected back and forth along the cochlea, stimulating the hair cells, leading to a self sustaining oscillation

As stimulus duration increases, what happens to threshold?

decreases

A stimulus generated at 0 azimuth, 90 vertical is located

directly above the listener.

Why is the minimum audible pressure (MAP) curve poorer (i.e., higher thresholds) for higher frequencies?

earphone calibration

Interaural time differences

from 90 to 270 or 270 to 90 Independent of frequency Provides localization information for low frequency stimuli (phase-locking) takes .6 ms for sound to go from one side to the other low frequencies bend around obstacle -only coming from 90 or 270 -localize low frequency based on timing cues, little or no loss of acoustic energy -SOC depends on timing cues (low freq) Speed of sound formula

MAP-Inserts

go into ear canal -up to 8,000 Hz

Periodicity Pitch

The period of this complex tone is 10 sec, which is equivalent to 100 Hz The perceived pitch is equal to the reciprocal of the period Relies on period component instead of acoustic characteristics.

The measurement of minimum audible pressure (MAP) is characterized by

monaural stimulation presentation under earphones

The pitch-to-mels scale can be described as

nonlinear

Binaural hearing

Two ears are better than one Binaural threshold will be approximately 3 dB better/lower than the monaural thresholds Symmetry between the ears (equal thresholds) Best at 0 degrees azimuth and elevation out front (eliminates interaural time differences)

What is the most vulnerable portion of cochlear anatomy to noise?

stereocilia -allow depolarization not all noise causes hearing loss, effects different areas differently

Thresholds of audibility

the thresholds relating the smallest level required for detection to the frequency of the tone

Gap detection

until a difference is detected, widen the gap

Dissonance

when two sounds are presented together that result in an unpleasant perception

Pitch to mels graph

x axis: Hz Y axis: mels nonlinear manipulate freq. only, level is fixed 1000 Hz = key frequency

loudness level contour map

x axis: Hz y axis: dBSPL -measured in phons -manipulating both frequency and level -

loudness graph

x axis: dB HL y axis: sone (1 sone) keep a fixed frequency only change level until perceived as twice as loud

Effects of level on pitch graph

x axis:dB HL or SPL y axis: change in pitch -keep fixed frequency, adjust level lower: less than 1,000 Hz middle: 1,000-3,000 Hz high: greater than 3,000 Hz

Name two internal factors that affect threshold measures?

Vascular or respiratory noise Attention span

Differences between MAF and MAP

-MAP is monaural and MAF is binaural -Shape of the head, the Pinna and the ear canal influence of the MAF curve (minimized by playing speaker in front at 0 degrees there will be zero interaural time difference) -MAP is poorer in the lower frequencies because of the internal nose trapped in the ear canal by the earphones,can be any of the three types of earphones. -MAP curve is poorer in the higher frequencies because of the middle-ear characteristics or calibration of earphones High frequencies: less energy middle ear =less energy in cochlea=higher(worse) thresholds

Interaural level differences

-from 90 to 270 or 270 to 90 low:little or no level change high: level change -high frequency relies on timing difference, but we also get level difference because of shadow effect -talking about pure tones/also applies to multi -Frequency dependent -low diffract around and there is a timing difference for high -provides localization information for high frequency stimuli because of the head shadow effect -applies to both single and multi frequencies -because high frequencies do not bend around obstacles well, the opposite ear has a decrease in dB wavelength formula = ss/f....when freq goes up, wavelength goes down, inverse

Effects of inaccurate threshold

-higher output means you are letting people with hearing loss think there is no problem

Masking Level difference (MLD)

-improvement in threshold for a dichotic listening situation/more complex -the difference between a dichotic listening situation and a monotic listening situation -MLD is largest for low frequencies (about 15db at 500Hz) and decreases for higher frequencies (only 2-3 dB at 2000 Hz) Lower is better

Consonance

-pitch perception attribute - when two sounds are presented together that result in a pleasant perception -music related, subjective, perceptual

Timbre

-pitch perception attribute -differentiates two or more sounds that have the same pitch, loudness and duration -music related, subjective, perceptual

Loudness

-the perception of intensity (your perception) -measures in sones -frequency stays fixed, manipulate level. the person is asked to double the loudness. 40 dB @ 1,000 Hz = 1 sone. Only went up 10 dB (average) of how much normal person increases level when asked to double loudness. -the loudness or 1 sone corresponding to a loudness level of 40 phons -closer to threshold, difficult to hear things and differentiate Loudness counter: significantly above threshold, contour more linear -everyone differs -Intensity and loudness are not the same -Intensity doesn't change with frequency

Minimum Audible Angle(MAA)

-the smallest angular separation between two loudspeakers that a listener could detect -# in degrees you can differentiate sound coming from two speakers -can't move head -two separate tones from two different speakers sequentially -figure out if they are coming from one or two speakers -Listeners will require a larger angular separation between speakers as the speaker are moved from directly in front of the listener toward one ear -has to be increased when lateralized to one side -easiest to tell difference when right in front

Psychoacoustics

-the study of psychological response to acoustical stimulation -how you process sound and speech and respond to it

Stimulus Duration

-when the duration is shorter the threshold becomes higher -the tone does not become easier to detect with duration exceeding 200 ms -For durations between 10-200 ms, level increases as duration decreases -duration less than or equal to 10 ms cause a spread of excitation to other more detectable frequencies -greater basilar end displacement towards end and not in lower frequencies

When presented sufficiently above threshold, how much of an intensity difference is needed to discriminate between two intensities?

.5-1 dB

Calibration

- does the number on the audiometer equal the number in the headphones? -if the headphones are out of calibration, you will think thresholds are higher or that they have a hearing loss when they don't - check calibration in earphones every 6 months

Pitch

Pitch - the perception of frequency High Pitch - high frequency Low pitch - low frequency

Pitch Scale

Pitch is expressed in Mels S.S. Stevens 1930's developed Mel scale -Tell person to change frequency until they think it has doubled in pitch nonlinear

Frequency Discrimination

-Frequencies less than or equal to 1,000 Hz only need a 1-2 Hz change in frequency to notice -Frequencies greater than 1,000 Hz need a larger change -4,000Hz: 11-15 Hz change -5,000 Hz: 20-25 Hz change If you present 1,000 Hz and 1,002 Hz there is a noticeable difference -Higher HZ need a bigger change for the difference to be noticeable

Problems with masking experiments

-Individual will hear "beats" (adding and subtracting of traveling wave/up and down in level) -Nonlinearity of the cochlea (harmonics and combination tones) -create distortion products/ other frequencies -along with frequency we send cochlea will generate other frequencies which listener may perceive -Upward spread of masking (up in frequency number,physically down in cochlea, down in basilar membrane) -problem because you are covering up tones you don't want covered -person may have sensitive hearing and hear other frequency - turning level up causes greater displacement in basal end -

Differential Sensitivity

-Just noticeable difference or difference limen - smallest change in the stimulus that is detectable - differentiate frequencies -differentiate intensity level -differentiate time components

Loudness Level

-Measured in Phons 1,000 Hz tone at 40 dB SPL = 40 phons Person is given reference (1,000 Hz @40 dB SPL)tone and a second tone and is asked to manipulate the level until they perceive them as the same loudness level, All other frequencies judged equal in loudness to a 40 DB SPL, 1000 Hz tone and are said to have a loudness level of 40 phons For a given line, all the points are heard as having an equal loudness level to the given point Starting point always at 1,000 Hz Perceived as equal in loudness level, but not equivalent in intensity curve flattens as it gets higher in level -Perceived by person as being equal level Loudness level contour - nonlinear

Weber's Law

-Ratio between the size of the change and the magnitude from which the change was made - change in stimulus over original stimulus point -only holds for middle frequencies 500-2,000hz -holds when sufficiently above person's threshold (even just 10 dB) -closer to threshold, the difference needs to skyrocket, because its more difficult to hear -For intensity - works for only wideband stimuli (multiple freq) -still only works above threshold up to high levels for wideband stimuli -gonna suck near threshold

Minimal Audible Pressure (MAP)

-Same procedures except the individual is under earphones -different listening scenario -test one ear at a time (Monaural) -everyone has different amplification characteristics (this takes that away)

Intensity Discrimination

-Sensitivity across a broad change of frequencies -discriminate about .5 to 1 dB from 250 to 8,000 Hz -very good above threshold at numbers that aren't uncomfortable -closer to threshold the difference needs to be bigger -Wideband stimuli = multiple frequencies at or near threshold -Weber's better in lower freq. up to 1,000 Hz

Lateralization

-The listener will perceive a fused image that lies within the head -Under earphones -different than localization -everything fused centrally -hearing loss favors better ear Interearphone level difference - one louder than the other when frequency differs 250-300 Hz sounds like two different sounds, not fused when ineraural time difference get greater than about 2 ms, you are probably gonna perceive two different things

Temporal Discrimination

-Time - Gap Detection -200msec tone - 10ms silence - 200 msec tone -200msec tone - 20ms silence - 200 msec tone Is the silent interval the same or different? -Weber's law doesn't hold at all

Interaural phase difference

-Timing is most helpful -Will vary with frequency -Listener will have more difficulty localizing sounds with frequencies around 2000 Hz, it's possible that person will hear a tone at 2000 from right or left and think its coming from in front of them , auditory confusion anytime you think the intramural difference is zero, it is thought that the sound is coming from out front difficult because of the period of that distance is 0.6 Superior Olivary Complex also recognizes differences in phase -from 90 to 270 specifically -the distance from one ear to the other is approximately 22-23 cm so it will take the sound about .6 ms to get form one ear to the other -auditory confusion, sound coming from right or left but sounds like it's coming from front (when interaural difference is 0)

Minimum Audible Field (MAF)

-Uses a loudspeaker -Binaural, no earphones -Reveals auditory sensitivity for the human auditory system - Maximum sensitivity is between 2,000 and 5,000 Hz - Frequency range for humans is from 20-20,000Hz -indicates where the lowest/best thresholds are -not linear because we are not good at all frequencies -MAF Thresholds are usually determined for listeners facing the source, listening with both ears at one meter from the sound source Goal: the lowest and best frequencies

Threshold

-a certain intensity above which the organism always responds to the stimulus and below which it never does -LOWER THRESHOLDS ARE BETTER!!! -not a uniform agreement across alls studies -Threshold varies from moment to moment because of internal and external factors -Thresholds can go down to -10 dB

Precedence Effect

-all parameters being calculated by the one ear first ( the first ear) -first acoustic stimulus getting to one ear is going to dominate your ability to localize sound and overcomes 2,000 Hz phase difference problem or reflecting sounds. The first acoustic stimulus arriving at the ears dominates in establishing the location of the stimulus by suppressing the remaining acoustic stimuli This effect overcomes the 2000 Hz localization problem -1st sound to get to ear, first come first served

Critical Band Masking

-internal filter: peak of where stimulus occurs, what basilar membrane is doing -Internal filter helps to determine the detection of a signal in the noise -triangle represents peak of traveling wave and what frequency does at stimulus point -less acoustic energy bombarding signal area - not bombarding internal filter with background noise Critical band - the frequencies within the passband of the Internal Filter that were critical for the masking Look at graphs: A: everyone talking and flooding the internal filter B: two rows of people talking not as much bombardment, not all of the internal filter is covered

Auditory Nerve Fiber Damages

-no amplification or cochlear implant for this -basal end: high frequency hearing loss -need neural pathway to leave cochlea to CNS

Masking

-not always a tone, can be any noise like speech, etc. -changing freq and looking for level (volume) that covers stimulus tone the shift in threshold of one tone due to the presence of a masking tone -low freq. better at masking high -height of frequency wave depends on intensity Basal end: high frequencies Apical end - low frequency -effective masker covers up the tone -the key is to change the signal - noise ratio -establish threshold and go slightly above it -

Threshold of pain

120-130 dB

What is the masking level difference (MLD) for higher frequencies?

2-3 dB

Human frequency range

20-20,000 Hz

What is the approximate frequency range of human hearing?

20-20,000 Hz

What is the frequency region of maximum auditory sensitivity (i.e., lowest thresholds) for humans?

2000-5000Hz

What is the physiologic basis for the upward spread of masking?

Basilar membrane mechanics

Why is the binaural hearing threshold approximately 3 dB better (or lower) than a monaural threshold?

Because of the 10log102:1 formula.

Binaural hearing in the vertical plane

The listener is not as good at determining the vertical localization compared to the horizontal location Fix the problem by moving your head Extreme height difference when all else fails minimize interaural differences by moving your head.

Clinical Masking

Eliminate the influence of the better ear, sometimes you have to turn up tone so loud for bad ear that it crosses over and is heard by better ear, so we eliminate influence of better ear by present tones to poor ear Better representation of everyday listening situations Narrow band noise is used to mask during pure tone audiometry (only use pure tones when testing, noise that is narrowly tuned around pure tone frequency is used to mask opposite ear, waste time if white noise is presented) Speech noise is used to mask during speech testing We want speech noise between 500-2,000 hz Applies to unilateral hearing loss(one ear sufficiently better than other)

Internal and External factors that affect threshold

External: instrumentation, procedural limitations,sound proof testing environment Internal - vascular (biological) noise, attention span -test at 250, 500, 1,000 Hz -most likely below 1000 Hz

Level effects on pitch

For 1,000 Hz and below- increase in level causes a decrease in pitch Between 1000 and 3000 Hz- pitch remains constant with an increase in level For 3000 Hz and above - increase in level causes an increase in pitch Frequency fixed, adjusting level x = change in level y = perceived change in pitch

Binaural hearing in the horizontal plane

For broad-band noise the listener is very good at localizing the noise -Ex: person in chair with speakers surrounding them,(broadband noise, multiple frequencies),....person has to focus on the one speaker out front and can't move their head. Two separate tones come out of two different speakers, sequentially. Listener has to say if they came from one speaker or two, must stay focused at 0 azimuth. MAA is very small when signal is from speaker is out front When moved to the side,but person stays facing forward, the MAA angle gets bigger. -MAA (# in degrees that you can differentiate the source coming from two separate speakers)

Basilar Mechanics

Hard to cover up traveling at high frequencies because it drops off -sometimes can't turn up a high freq basal end tone loud enough to mask low freq apical tone without hurting listener, tones may be too far apart -upward spread of masking -no physically up because in cochlea it is actually down - low frequencies travel up the apical end and have more of a chance to mask the frequencies lower - better masker -tonotopic organization

More severe noise damage

IHC's and OHC's damaged a=happy b=damage c=structure damage in inner and outer cells

Initial noise damage

IHC's and OHC's intact(below the surface), but stereocilia(more vulnerable) of OHC's damaged damage to stereocilia - limit opportunity for potassium to enter the cells

Moderate noise damage

IHC's intact, but OHC"s damaged -permanent damage -IHC's have more structural support than OHC's (fluid surrounded) -limited info leaving cochlea -Can sometimes get away with OHC and sterocilia damage but with IHC's stereocilia it's much worse because no neural messages leaving

Localization

Identify a sound in space No earphones

Loudness Adaptation

Match the level of a comparison tone to the level of sn adapting tone Turn the comparison tone off and leave the adapting tone on for a period of time Match the comparison tone again, but this time it will be at a lower level even though the level of the adapting tone is the same 2nd comparison lower than the initial -over time your auditory system gets used to loud level,

Psychophysical Tuning Curves

Individuals with cochlear hearing loss have more broadly tuned PTC's even at characteristic frequency -sharper tuning curves better at frequency discrimination -lose that characteristic with broad tuning curves -increase in threshold = damage permanent threshold shift: lack of frequency discrimination even raising level won't help.

Noise Stimuli factors

Level: more level = more damage Duration: longer = more damage Frequency - for moderate levels or short durations, the TTS will occur at the frequency of the exposure stimulus For higher levels, the TTS usually occurs around 3-6 kHz *Continous noise not blasts -damage coincides with frequency noise induced notch around 1000 Hz Frequency specific damage: when level is high enough you see damage at that region along basilar membrane, where then frequency input is but if we get to a point where we turn up the level too high, we are going to cause damage potentially away from the stimulus input

Are intensity and loudness the same?

No, loudness is the perception of intensity.

Notch-Noise Masking`

Noise bands are on either side of the internal filter Combo of high and low pass filters As the spectral notch gets bigger (in Hz) less noise energy goes through the internal filter narrow notch = more noise going through internal filter Straight path but outside noise makes it difficult With wider width,signal is easier/better = lower threshold narrower = harder to hear signal, higher threshold

Masking level difference for low frequency stimuli

Non-zeros are dichotic m=master of noise s=signal (pure tone single frequency baseline threshold = 25 dB dichotic for low frequency stimuli *Look at slide 18

Head related transfer functions (HRTF's)

Person sits in environment and you present a broad band/ white noise out of the speakers. Has a probe microphone in ear, plays stimulus through each speaker all the way around and going to record what is getting to the ear canal. Acoustic energy that gets to tympanic membrane will never be the level that is being presented. Take all the frequency response curves and paste them together and generate a new stimulus and present it over earphones. Auditory illusion, not fused image in head. Measure the acoustic spectrum by stimulating with a wideband noise and recording the noise with a probe microphone near the TM Present the stimulus under earphones and it appears to be coming from space rather than than in the head White noise or broad band -sound field representation, put frequency responses together to make new stimulus

Phons and Sones

Phones - loudness level equivalent, nonlinear scale where you manipulate both freq and level Sones - twice the loudness or half the loudness of a reference stimulus (1000 Hz @ 40 dB SPL) freq. is fixed, only manipulating level

The unit of measure for loudness level is

Phons

Tonal Masking

Present a 1000 Hz signal tone at a low level while simultaneously presenting another masking tone at a different frequency and the listener is asked to detect the signal tone. -diotic- two tones to one ear -signal tone always fixed, masker is manipulated until effective -volume is up and down -Using pure tones, turn master level up until the person can only hear one tone Ineffective masker: when a high level masker is presented and the person can still hear the signal tone,no matter how high levels turned up, two tones can still be heard Effective masker: a low level masker causes the signal to tone to be undetected... Any tones above masking threshold will always be heard as one outside tuning curve = heard as two tones inside tuning curve = always heard as one, effective picture ex shows signal tones = 300@41,1000@22,3000@20 all other shapes plotted, are effective maskers tuning curves broader in low freq and sharper in high freq

Missing Fundamental

Present a complex tone with energy at 300, 400, 500, 600 and 700 HZ (odd and even integer multiples: sawtooth wave) Individual has to match the pitch of the complex tone to another tone, manipulating freq. level fixed, freq change -Individual will judge the sound as having a 100 Hz pitch because of 10 ms period. -100 is lowest integer multiple, corresponds to period of complex tone People will match the complex tone to 100 Hz Complex tone in one ear and manipulate frequency in other ear

Weighting Scales

Rough Approximations of various phone curves -measuring sensitivity in sound field -we used specific weighting scales in an environment -A, B, C Scales -A: filtering out more low frequencies, more approx. Dominantly dBA scale Decibel level a:lowest(very selective, filters out most, rough approx of what auditory system is doing) b:middle c:highest (all sounds are welcome, shows all info that gets to TM)

MAP-TDH

Supra-aural -top of ears -stops at 8,000 Hz, can't go above -125-8,000 Hz

Noise and Hearing Loss

Temporary threshold shift (TTS) -resilient, probably still some damage, thresholds increase, down on audiogram, temporary damage, recovered in about 24 hrs -occurs at 3,000-6,000 Hz Permanent threshold shift (PTS) -post exposure thresholds that do not return to pre-exposure levels hearing lose x>25 dB

In a notch-noise masking condition, as the spectral notch gets smaller, what happens to threshold?

Threshold increases

Noise Masking

White noise - equal energy at all frequencies, but the spectrum changes because of the earphone and ear canal characteristics...never reaches tympanic membrane, earphones aren't calibrated to deliver equal energy across all frequencies Signal-to-noise (S/N) ratio needed to mask changes as a function of frequency signal =40dB noise = 60dB .......-20dB signal = 50 dB noise= 40dB S/N = +10 dB -we are good at + S/N ratios - change frequency and determine signal-noise ratio on graph: as I increase frequency, I have to increase level or the S/N ratio goes up -moving freq and looking to see what the S/N ratio is to recognize the frequency -if a tone is graphed at 8dB it means it needs to be 8dB above the signal tone to be heard -

As less noise passes through the internal filter, detection of the signal of interest

becomes easier

Interaural level differences (ILDs) primarily help you localize which frequencies?

high frequencies

When a speaker pair is moved closer to either 90 or 270 azimuth, what happens to the minimum audible angle (MAA)?

increases

Volume

increases as the frequency and intensity decrease inversely proportional

Density

increases as the frequency and intensity increase directly proportional