Sound Field Testing

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Sound Field Testing

• MCHAS TEAM

Wave 4 SFR 17/05/04
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What can aided sound field thresholds tell us?
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Aided Thresholds
A
A
A
A
A
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Limitations

• Relies on valid behavioural response

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Limitations

• Limited frequency resolution

VS
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Limitations

• No information on real ear output characteristics
  HA

X
X
X
X
X
X
A
A
A
A
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Limitations

• Poor test-retest reliability
• Need at least 15 dB difference between conditions
  before significant effect (Hawkins 1985).

A
A
A
A
A
A
A
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A
A
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Limitations

• Provide little indication of speech audibility,
  especially when using WDRC.

Seewald 2003
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Limitations

• Inaccurate in regions of normal hearing

X
X
A
A
A
A
A
A
X
X
X
X
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So what information is provided?

• An indication of the childs/infants auditory
  performance
• Good visual/auditory demonstration to parents
  between no hearing aids vs hearing aids.

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A word of caution

• Be aware of possible interactions with hearing
  aid features.
• Number of channels
• Compression speed
• Noise algorithms
• Active feedback control

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A word of caution

• Take care in testing setup
• Loudspeaker listener in calibrated positions
• Quiet room
• No movement
• Ascending warble tones
• Stimulus duration approx 1 sec
• 5 dB steps
• Inter-stimulus interval of at least 5 sec
• Individual ear information

Nelson 2003 AAA
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A word of caution

• A 5 year old child with a 90-100 dB flat loss is
  fitted with a power WDRC DSP hearing (no volume
  control) analogue linear power hearing aid with
  volume control. Would you expect any differences?

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0
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A
10
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20
30
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Linear aid volume control had been increased
prior to testing.
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Hearing Threshold
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WDRC DSP Aid
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100
110
120
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140
.125
.25
.5 1 2
4
8

Frequency (Hz)
Nelson 2003 AAA
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What the Aided Threshold is and is not

• IS -index to reflect softest perceptible sound
  w/o vc
• -Functional gain reflects gain for softest
  sound (not conversational level)
• IS NOT
• -Reflect gain for any input level other than
  soft
• -Reflect gain for conversational sounds
• -Reflect loudness comfort
• -Reflect processing of DSP aids eg. NR etc
• Kuk, F
• (AAA 2004)

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What Real-Ear Measure is and is not

• IS-Allows determination of physical output of
  hearing aid at different input levels Gain for
  conversational, soft and loud sounds
• Effect of signal processing eg.compression, NR
  etc
• IS NOT-A perceptual response ie. Does not tell
  how soft a child can hear
• -cannot predict aided threshold
• Kuk, F
• (AAA 2004)

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So, should we be using both for a fuller picture?

• Perhaps
• If so, what should be the optimal aided
  threshold?
• Depends on criteria
• Importance of hearing soft or low level input
• sounds and meaningfulness of these
• Degree of hearing loss and possible dead
• regions
• Limitations of hearing aid (as discussed)
  

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THANK-YOU!