Download Modernising Children`s Hearing Aid Services

Sound Field Testing
MCHAS TEAM
Wave 4 SFR 17/05/04
Modernising Children’s Hearing Aid Services
What can aided sound field thresholds tell
us?
Modernising Children’s Hearing Aid Services
Aided Thresholds
10
0
10
20
30
A
A
40
A
A
A
50
60
70
80
90
100
110
120
130
140
125
250
500
1000
2000
Frequency (Hz)
4000
8000
Modernising Children’s Hearing Aid Services
Limitations
 Relies on valid
behavioural
response
Modernising Children’s Hearing Aid Services
Limitations
Hearing Threshold
 Limited frequency resolution
10
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
A A
.125
.25 .5
A
A
1
24
Frequency (Hz)
8
Modernising Children’s Hearing Aid Services
Limitations
dB SPL (TM)
 No information on real ear output characteristics
HA
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
X
X
A
125
250 500
X
X
A
X
A
1000
X
A
2000
4000
8000
Frequency (Hz)
Modernising Children’s Hearing Aid Services
Limitations
 Poor test-retest
reliability
10
0
10
20
30
40
50
AA A
A
60
70
A
A
A
A
A
A
80
90
100
110
120
130
140
125
250
500
1000
2000 4000
Frequency (Hz)
8000
 Need at least 15 dB
difference between
conditions before
significant effect
(Hawkins 1985).
Modernising Children’s Hearing Aid Services
Limitations
 Provide little indication of speech audibility,
especially when using WDRC.
Seewald 2003
Modernising Children’s Hearing Aid Services
Limitations
 Inaccurate in regions of normal hearing
10
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
X
A
X
A
A
X
125
250
A
A
A
X
X
500
1000
2000 4000
Frequency (Hz)
X
8000
Modernising Children’s Hearing Aid Services
So………… what information is provided?
 An indication of the
child’s/infant’s auditory
performance
 Good visual/auditory
demonstration to parents
between ‘no hearing aids’
vs ‘hearing aids’.
Modernising Children’s Hearing Aid Services
A word of caution
Be aware of possible interactions with
hearing aid features.
Number of channels
Compression speed
Noise algorithms
Active feedback control
Modernising Children’s Hearing Aid Services
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)
Modernising Children’s Hearing Aid Services
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)
Modernising Children’s Hearing Aid Services
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)
Modernising Children’s Hearing Aid Services
THANK-YOU!
Modernising Children’s Hearing Aid Services