Post on 11-Aug-2020
Institut für Schallforschung, Österreichische Akademie der Wissenschaften; A-1010 Wien, Reichsratsstrasse 17
Tel: +43 1/4277-29514 Fax: +43 1/4277-9295 email: Bernhard.Laback@oeaw.ac.at
Envelope vs. Fine Structure in Bilateral Hearing
Bernhard Laback1, Piotr Majdak1, and Wolf-Dieter Baumgartner2
1 Acoustics Research Institute, Austrian Academy of Sciences2 ENT-department, Vienna University Hospital
6th Meeting on Bilateral CI and Binaural Sigal Processing, BernMarch 30, 2007
http://www.kfs.oeaw.ac.atBernhard.Laback@oeaw.ac.at
Sound Source
ITD Interaural Time Differences (ITDs) occur in
• Gating portions (ITDON/ITDOFF)
• Temporal fine structure (ITDFS)
• Ongoing envelope (ITDENV)
ITDONITDOFF
Interaural Time Difference (ITD)
Motivation for study
Fine structure ITD is important for • Lateralizing sound sources (Wightman and Kistler, 1992;
Smith et al., 2002) and for • Speech understanding in noise (Nie et. al., 2005; Zeng et
al., 2005)
CI listeners are often sensitive to ITD (e.g. van Hoesel and Tyler, 2003)
Open Questions: • Are bilateral CI listeners sensitive to ITD in the fine
structure? • What is the contribution of gating ITD and ongoing
envelope ITD?
Lateralization Discrimination of ITD in Fine Structure, Onset, and Offset: Four-Pulse Sequences
Laback, Majdak, and Baumgartner (2007) JASA 121 (April)
Study I
Methods I
Electric stimuli− Biphasic pulse trains (4 pulses) presented
at interaurally pitch-matched and loudness-balanced electrode pair (selected in pretests)
via Research Interface (RIB) with interaural accurracy of 2.5 µs
ITD conditions (see right side)
No Delay(comparison condition)
Waveform(Wave)
Ongoing
Onset
Gating
TimeAmpl
Offset
ITD
Left
Right
Left
Right
Left
Right
Left
Right
Left
Right
Left
Right
(≈ Fine Structure)
JNDs for Left/Right Discrimination
Subjects
− Four CI listeners (C40+, MED-EL), postlingually deafened, selected based upon minimum ITD sensitivity criterion
− Five NH listeners (listening to CI simulation)
Independent Variables− ITD condition
− Pulse Rate
Methods II
Expectations
Pulse Rate (pulses per second, pps)
Just
Not
icea
ble
Diff
eren
ce (µ
s)
Waveform ITD
Expectations
Pulse Rate (pulses per second, pps)
Just
Not
icea
ble
Diff
eren
ce (µ
s)
Waveform ITD
Onset ITD
Expectations
Ongoing ITD
Pulse Rate (pulses per second, pps)
Just
Not
icea
ble
Diff
eren
ce (µ
s)
Waveform ITD
Onset ITD
Results for CI listeners: CI1
100 200 300 400 500 600 700 800Pulse Rate (pulses per second, pps)
0
200
400
600
800
1000
JND
(µs)
CI1NDND Wave
OngoingGatingOnsetOffset
• Wave ITD sensitivity decreases with rate (p < 0.003)
• Ongoing ITD contributes at 100 pps only
• Onset ITD contribution increases with rate (p < 0.0001)
Results for CI listeners: CI12
100 200 300 400 500 600 700 800Pulse Rate (pulses per second, pps)
0
200
400
600
800
1000
JND
(µs)
CI12NDND Wave
OngoingGatingOnsetOffset
• Wave ITD sensitivity independent of rate
• Ongoing ITD contributes up to 400 pps
• Onset ITD contribution increases with rate (p < 0.034)
Results for CI listeners: CI8
100 200 300 400 500 600 700 800Pulse Rate (pulses per second, pps)
0
200
400
600
800
1000
JND
(µs)
CI8NDND Wave
OngoingGatingOnsetOffset
• Wave ITD sensitivity up to 400 pps only
• Ongoing ITD contributes up to 400 pps
• Onset ITD does not contribute
Results for CI listeners: CI3
WaveOngoingGatingOnsetOffset
100 200 300 400 500 600 700 800Pulse Rate (pulses per second, pps)
0
200
400
600
800
1000
JND
(µs)
CI3NDND
• Wave ITD sensitivity independent of rate
• Ongoing ITD contributes at all rates tested (up to 800 pps)
• Onset ITD contribution increases with rate (p < 0.04)
CI listeners are sensitive to ongoing ITD in four-pulse sequences, thus to “pure” fine structure ITD
Highest rate showing fine structure ITD sensitivity varies from 100 to 800 pps
Contribution of onset ITD increases with pulse rate (in three out of four subjects)
Conclusions of Study I
Lateralization Discrimination of ITD in Fine Structure and Ongoing Envelope: Modulated pulse trains
Majdak, Laback, and Baumgartner (2006) JASA 120, 2190-2201
Study I
Methods
Stimuli− Amplitude modulated pulse trains (300 ms)
(Fmod = 13 Hz)
Independent variables
− ITDFS: 0…IPI (inter-pulse interval)
− ITDENV: 0…800µs
− Pulse rate: 100 … 1600 pps
Subjects − 4 CI listeners (postlingually deafened)− 4 NH listeners (listening to CI simulation)
Expectations
½ IPI IPI0%
Late
raliz
atio
n di
scrim
inat
ion
bette
rbe
tter
ITDENV= 0 µs
¼ IPI
100%
-100%
¾ IPIITD FS
„correct“ side
„wrong“ side
½ IPI IPI0%
Late
raliz
atio
n di
scrim
inat
ion
bette
rbe
tter
ITDENV= 0 µs
ITDENV > 0
¼ IPI
100%
-100%
¾ IPIITD FS
„correct“ side
„wrong“ side
Expectations
Results for Lower Pulse Rates
Results for Lower Pulse Rates
0 2 0 0 0 4 0 0 0 6 0 0 0 8 0 0 0 1 0 0 0 0- 1 0 0
- 8 0
- 6 0
- 4 0
- 2 0
0
2 0
4 0
6 0
8 0
1 0 0
I T D F S i n µ s
Late
ralis
atio
n di
scrim
inat
ion
in %
C I 2 - 1 0 0 p p s
E N V = 0 µ s
E N V = 6 2 5 µ s
E N V = 8 0 0 µ s
m e a nm e a n
m e a n
P R = 4 0 0 p p s
Results for Higher Pulse Rates
Sensitivity to Fine Structure ITD
Pulse rate CI1 CI2 CI3 CI8100 < 0.001 - -150 < 0.001 - -200 < 0.001 0.01 - -400 0.75 0.21 < 0.001 < 0.001600 - - - -800 - - <0.001 <0.001938 - - - 0.451600 0.46 - 0.11 -
NHs - - -
< 0.001< 0.001< 0.139< 0.712
-
High sensitivity to ITDFS (in 2/4 subjects up to 800 pps)
Low sensitivity to ITDENV (low modulation rate)
High inter-subject variability of performance
Conclusions of Study II
CI listeners are likely to benefit from encoding fine structure ITD at lower rates in CI systems
The highest rate providing fine structure ITD cues is lower than in acoustic hearing with sinusoids (up to 1500 Hz)
Overall Conclusions