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Flashcards in Lecture 3 Deck (18):
1

What is the definition of threshold (usual and clinical)?

Definition of threshold:

• Usual definition –faintest level of a signal that a listener can detect

• Clinical operational definition: lowest intensity level of a signal at which the listener responds 50% of the time (attention fluctuates) 
 

2

What are two psychophysical methods of assessing threshold? Which would produce a better threshold and why?

 Psychophysical methods of assessing threshold:

• Single stimulus technique –present stimulus during each observation interval, listener indicates if he or she heard it or not (vary intensity level, fix frequency)

• Forced-choice technique –mark off two or more observation intervals; signal is present in one interval; listener must indicate in which interval they heard the stimulus (consider guess rate)

  • Have to increase definition of threshold (usually 75%)
  • Would produce better threshold because it rids of listener bias (if listener isn't sure in single stimulus, maybe won't respond)
     

3

For the single stimulus technique, what are 2 methods of presentation? Explain each. 

single stimulus technique –2 methods

• method of limits –tester controls level & presentation

  • Ascending method of limits: start at low level and increase level until response
  • Descending method of limits: start at suprathresholdlevel and decrease level until NR

• method of adjustment  

  • Listener controls intensity level of signal (until they think they can just barely hear) 
  • Ex: Bekesy audiometry, automatic audiometry
     

4

Explain the signal's path through both air and both conduction.

Air conduction:

• Signal delivered to EAC -> t.m. -> ossicular chain -> oval window -> compression & rarefaction of cochlear fluids -> neural stimulation -> CANS

Bone conduction:

• Signal delivered to mastoid bone  or forehead -> vibrates bony labyrinth -> stimulates inner ear fluids -> neural stimulation -> CANS

5

What is the preferred method for air conduction threshold testing? Describe the instructions, prepatory phase, and test phase. What should the signal duration be? Why? What should the intersimulus interval be? Why? What percentage of the clinical population does this technique work for?

Preferred Method -modified Hughson-Westlake technique (Carhart& Jerger, 1959; ASHA, 2005)

• Instructions

  • Respond when tone goes on and off

• Preparatory Phase - training what to listen for

  • Present first signal at suprathreshold level (30 –40 dB HL) 
  • With initial response, descend in 10 dB steps until NR

• Test Phase

  • Ascending in 5 dB steps until response,
  • descend in 10 dB steps until NR
  • Continue until 3 responses at same level on ascending runs = θ
  • signal duration (> 200 ms and < 2 sec)
    • if shorter than 200 ms, need to increase intensity
    • 200 ms - time it takes to integrate level of signal over time
    • Not longer than 2 sec because most sensitive at onset. 

• interstimulus interval –at least 1-2 sec

  • For recovery of 8th nerve (refractory period)

Works for 80% of clinical patients

6

What are the sources of variability in air conduction testing (11)?

  • seating arrangement
  • Patient’s readiness to listen
  • instructions
  • earphone placement 
  • Initial test ear
  • order of frequencies;  test frequencies
  • Inter-stimulus interval (ISI)
  • standing waves
  • false responses;  pulsed v. continuous tones
  • collapsed ear canals
  • Acceptable test-re-test reliability

7

Explain how to control for variability in seating arrangement, readiness to listen, and instructions.

  • Seating arrangement
    • Want to see their face, but not have them face you
      • don't want them to see your visual clues
      • want to see their visual cues
  • Readiness to listen
    • too nervous? too sleepy?
    • Change the way you interact with them based on that
  • Instructions
    • Press the button, even if the tone is very soft 

8

Explain how to control for variability in placement of the earphones, initial test ear, and order of frequencies.

  • Earphone placement
    • remove glasses, earrings, hats (interfere with tightness)
    • diaphram should be over opening of external auditory canal
    • Can vary thresholds by 15 dB
  • Initial test ear
    • start in better ear (ask them)
    • start in right if don't have better ear (by convention)
    • Start in better because may need to mask in poor ear and need thresholds in better ear for that
  • Order of frequencies
    • Start with 1000 Hz because people hear best there (still training)
    • Retest at 1000 - tests listener reliability
    • Now it is more standard to test 3 kHz and 6 kHz because of noise exposure (notch can be at 3, 4, or 6 kHz) 
    • Test ultra high freqs if hearing gets better at 8 kHz
    • Test 125 hz if have severe to profound hearing loss in the normal range. To see if you can get some measure of hearing sensitivity

9

Explain how to control for variability in ISI, Standing waves, and false responses

  • ISI
    • Stagger - break pattern 
  • Standing Waves
    • Avg. length of ear canal is 1.5 in. 
    • Wavelength of 8 kHz is 1.5 in
      • reflected tone from tm can cancel incidence tone
      • Will show a big drop at 8 kHz
      • Can ask them to hold ear phone slightly away from their ear or can use inserts.
  • False responses
    • false positive - didn't present tone and they are responding
      • Can be because of tinnitus
      • Pulsed tone can hellp with tinnitus
    • Reinstruct, or descend to threshold and go all the way back up

10

Explain how to control for variability in collapsed ear canals. What is the acceptable test-retest reliability of air conduction thresholds?

  • Collapsed ear canals
    • 4 or 5% of population
      • 10-36% in elderly 
    • Can't get benefit of high frequency resonances
    • Will see a high frequency conductive hearing loss
    • Use inserts
  • Acceptable test-retest reliabilty - 5 dB

11

What is an alternate method of testing air conduction pure tone thresholds? How is it done? Who does it help?

  • Pulsed-tone method
    • “Count the beeps”
  • Procedures
    • How many beeps did you hear? 
  • Helps individuals with tinnitus, helps kids
    • distracts from tinnitus

12

What are the theories of bone conduction? Explain each

Theories of bone conduction

• inertia mode (Bekesy, 1932, Barany, 1932)

  • Occurs for signals 800 Hz and below
  • Skull moves as a unit but ossicular chain lags behind
  • Medial wall vibrates over footplate of stapes

• compression mode

  • Occurs for signals > 800 Hz (begins at 800 –1600 Hz)
  • Skull moves segmentally in different directions at the same time, causes inner ear spaces to change volume and compress fluid

• external-canal mode (Tonndorf, 1966)

  • With b.c. stimulation, also causes vibration of EAC -> resonances -> tm vibrations (hearing by a.c.)

13

Describe the measurement of bone conduction thresholds. Placement, procedure, interpretation. 

  •  Placement: mastoid or forehead
  • Procedures: modified Hughson-Westlake technique
  • Interpretation of b.c.θs –true measure of cochlear reserve?
    • not 100% reflection of sensitivity of cochlea 
      • because of external canal mode
      • otosclerosis - abnormal process of bone around footplate of stapes - fixates stapes in oval window - middle ear disorder
        • Will show a Carhart notch in bone conduction 
          • 500 Hz - 5 dB, 1000 Hz - 10 dB, 2000 Hz - 15 dB, 4000 - 5 dB
        • Post surgery, bone conduction will be at 0 dB, so bc can't be true measure of cochlear ability

14

What are some unusual bone conduction findings? Describe each

 Superior Semicircular Canal Dehiscence (SSCD) –opens a 3rd window in inner ear (thinning of membrane) 

  • AC stimulus reaching inner ear is shunted through the 3rd window (dehiscence)
    • decrease in AC thresholds
  • BC thresholds may be improved through the skull’s response through the dehiscience
  • May see air-bone gaps up to 60 dB (esp in low frequencies) - pseudo-conductive components

Enlarged Vestibular Aqueduct (EVA, LVA)

  • Congenital disorder where vestibular aqueduct (regulates endolymph) > 1.5 mm
  • Hrgloss is sensorineural in nature, but frequent reports of mixed loss (low frequency component)
  • Source (UK): abnormal endolymphatic pressure, stapes fixation, incomplete development of stapes?  

Suspected vibrotactilethresholds

  • Feel stimulus instead of hearing
    • 250 Hz - 35-40 dB
    • 500 Hz - 55-60 dB
       

15

What are sources of variability of bone conduction testing? Explain each

Sources of Variability

• Force exerted by bc vibrator on skull

  • Force less than 400 g - low frequencies will be affected
    • needs to be tight

• Location –advantages/disadvantages of mastoid & forehead placement

  • Mastoid - more sensitive measure of threshold, but location matters on mastoid becaus some areas are more sensitive
  • Forehead - more reliable for placement, but less sensitive

• occluded vs. unoccluded: recall occlusion effect

  • Will show improvement Bone conduction.

Magnitude of Occlusion Effect : 

250         500        1000        2000        4000

20 dB     15 dB      5 dB           0 dB          0 dB

16

What are the standards for the audiogram form? 

Tabular or Audiogram Form

Audiogram form: (see ASHA guidelines and ANSI 2010 standards for audiometers)

  • Horizontal Scale is Frequency -Hz: standard range is 125 –8000 Hz, noted in logarithmic steps
  • Vertical Scale is Hearing Level -dB: range of dB: -10 -> 120 dB HL (or audiometer limits), should be linear in dB (increments of 10 dB or less)
  • Scale proportions: 1 octave (frequency) = length of 20 dB on HL scale (manual audiograms)

17

What are the symbols that are used to record thresholds?

look at slides

18

What infor should be included on the audiogram?

  • Date and location of test (ANSI: time of test)
  • Names of participant, audiologist
  • Professional credentials
  • Test equipment used & calibration info
  • Θ values at each frequency/ear by ac and bc
  • Explanation of symbols
  • Observations of physical condition of ears or patient behavior (ANSI: age, gender of listener)
  • Assessment of test reliability
  • Description of non-standard methods used
  • Reason for assessment