The impact of asymmetric stimulation rates on auditory ...€¦ · Auditory Object Formation....
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The impact of asymmetric stimulation rates on auditory grouping and binaural sensitivity in bilateral cochlear implant listeners Tanvi Thakkar 1 , Alan Kan 1 , and Ruth Y. Litovsky 1 1 University of Wisconsin-Madison, Madison, WI e-mail: [email protected] WAISMAN CENTER INTRODUCTION ACKNOWLEDGEMENTS REFERENCES SUMMARY METHODS Binaural Hearing and Speech Laboratory 2016 ARO MidWinter Meeting San Diego, CA Poster # 737 The aim of this study was to investigate how auditory object formation (AOF) occurs in BiCI listeners in the presence of interaurally asynchronous rates, and ITDs. Listeners responded on a single-interval, six-alternative forced-choice task (see Figure 1) using direct stimulation with synchronized research processors (Cochlear RF Generator) on a single pair of pitch-matched electrodes. Listeners (N=5) had the following individual characteristics: ITD conditions: ITDs of 0, -500, and + 500 us. * ITDs were randomized trial-by-trial. Rate conditions: Base rate of 100 pulses per second (pps) in left ear was held constant, while right ear was varied trial-by-trial at a percentage of the base rate, ranging from 25% below to 300% above, making a dichotic stimulus. *ITD was increased to ± 800 for listener IAU because they had an ITD threshold beyond 500 µs. “One-Left” “One- Center” “One-Right” “Left- dominant” “Center” “Right- dominant” Auditory Object Formation Binaural Sensitivity Binaural sensitivity to interaural timing differences (ITDs) in bilateral cochlear implant (BiCIs) listeners is remarkably variable, and it is presently not understood why this variability exists 2 . Prior research shows, pulse-rate discrimination in CI listeners reaches an upper limit of ~300 pps 3 when presented dichotically and monotically. Thus it is a possibility that BiCI listeners may not exhibit appropriate AOF when faced with certain differences between the ears other than binaural cues. RESULTS: What is the impact of dichotic pulse rates on auditory object formation and ITD lateralization? Auditory object formation (AOF) in normal-hearing (NH) listeners necessitates a set of grouping cues that provide the perception of a single auditory stream. However, when the stimulus is dichotic, AOF is limited when frequency-specific binaural channels are not matched 1 . Components that influence a listener's ability to successfully attend to a signal in noise include: Results suggest that dichotic rates presented to BiCI listeners can still lead to a fused auditory image. However, this does not necessarily lead to correct lateralization of the stimulus. Such a result would suggest that grouping of mismatched information may not lead to correct lateralization. Furthermore, pulse rate or pseudo-“pitch” may be a preferred strategy in deciding where the sound is heard for some listeners . 1. Steiger H. and Bregman, A. (1982b). Competition among auditory streaming, dichotic fusion, and diotic fusion. Perception & Psychophysics. 1982, 32(2), 153-162. 2. Kan A., and Litovsky RY (2015). Binaural hearing with electrical stimulation. Hear Res. 2015 Apr;322:127-37. 3. Carlyon RP., Long CJ., and Deeks JM (2008). Pulse-rate discrimination by cochlear-implant and normal-hearing listeners with and without binaural cues. J Acoust Soc Am. 2008 Apr;123(4):2276-86. 4. Krumbholz K., Patterson RD., and Pressnitzer D. (2000). The lower limit of pitch as determined by rate discrimination. J Acoust Soc Am. 2000 Sep;108(3 Pt 1):1170-80. We would like to thank all our participants and Cochlear Ltd for providing equipment. A special thank you to Rachael Jocewicz for her comments on the poster. This work is funded by NIH-NIDCD (R01 DC003083 to RYL), and NIH-NICHD (P30 HD03352 to Waisman Center). Left:100 pps & Right: 150 pps (example stimulus) Left:100 pps & Right:100 pps (i.e. matched pulse rates only) Dichotic pulse rate condition Figure 1: Example of response options Figure 2: Stimulus examples for diotic and dichotic pulse-rate conditions. Listener ID Age Years of CI experience (Bilateral) Etiology Electrode Pair # L R IBF 59 3 Heredity 12 12 IBK 75 5 Heredity 14 13 IBQ 80 6 Meniere's 14 7 ICJ 66 8 Childhood illness 20 16 IAU 68 12 Heredity (from birth) 12 11 Figure 3: Data from Carlyon et al. (2008): suggests that NH listeners can detect a dichotic F0 difference in pulse rates as small as 0.4% of 300 pps. Figure 4: Percentage of ‘One’ sound responses (“One- Left”, “One-Center”, or “One-Right”) across listeners. Assuming NH listeners can discriminate small rate differences between the ears, they would exhibit a narrow range of AOF for dichotic rates. NH listeners’ dichotic pulse-rate discrimination ability: BiCI listeners’ auditory object formation: BiCI listeners’ ITD lateralization (within all ‘One’ sound responses): Figure 5: Percentage of correctly lateralized ‘One’ sounds, with individual ITD thresholds labeled on right of the figure. Compare NH and BiCI populations ITD thresholds (µs) at 100 pps, dichotic pulse rates: IBF: ~62 µs IBK: ~52 µs IBQ: ~264 µs ICJ: ~203 µs IAU: ~638 µs Listeners with good ITD sensitivity showed AOF and lateralization when rates are interaurally matched. Listeners with poorer ITD sensitivity showed poor lateralization with dichotic pulse rates even in the presence of AOF. RESULTS: Perceived lateralization Response patterns across listeners appear to differ: A) IBK and IBF no longer lateralize the ITD of the perceived single fused image with the introduction of dichotic pulse rates B) ICJ, IBQ, IAU, lateralize by making more “left” and “right” decisions in the dichotic pulse-rate conditions. Figure 6: Percentage of lateralized ‘One’ sound responses per target ITD. ITD (µs) ITD (µs) Diotic pulse rate condition BiCI listeners show a broad range of tolerance for AOF with increasing dichotic pulse rates.
Transcript of The impact of asymmetric stimulation rates on auditory ...€¦ · Auditory Object Formation....
The impact of asymmetric stimulation rates on auditory grouping and binaural sensitivity in bilateral cochlear implant listeners
Tanvi Thakkar1, Alan Kan1, and Ruth Y. Litovsky11University of Wisconsin-Madison, Madison, WI
e-mail: [email protected]
WAISMAN CENTER
INTRODUCTION
ACKNOWLEDGEMENTSREFERENCES
SUMMARY
METHODS
Binaural Hearing and Speech Laboratory
2016 ARO MidWinterMeeting
San Diego, CAPoster # 737
The aim of this study was to investigate how auditory object formation (AOF) occurs in BiCI listeners in the presence of
interaurally asynchronous rates, and ITDs.
Listeners responded on a single-interval, six-alternative forced-choice task (see Figure 1) using direct stimulation with synchronized research processors (Cochlear RF Generator) on a single pair of pitch-matched electrodes.
Listeners (N=5) had the following individual characteristics:
ITD conditions: ITDs of 0, -500, and + 500 us. * ITDs were randomized trial-by-trial. Rate conditions: Base rate of 100 pulses per second (pps) in left ear was held
constant, while right ear was varied trial-by-trial at a percentage of the base rate, ranging from 25% below to 300% above, making a dichotic stimulus.
*ITD was increased to ± 800 for listener IAU because they had an ITD threshold beyond 500 µs.
“One-Left” “One-Center”
“One-Right”
“Left-dominant” “Center” “Right-
dominant”
Auditory Object Formation Binaural Sensitivity
Binaural sensitivity to interaural timing differences (ITDs) in bilateral cochlear implant (BiCIs) listeners is remarkably variable, and it is presently not understood why this variability exists2. Prior research shows, pulse-rate discrimination in CI listeners reaches an
upper limit of ~300 pps3 when presented dichotically and monotically. Thus it is a possibility that BiCI listeners may not exhibit appropriate AOF when faced with certain differences between the ears other than binaural cues.
RESULTS: What is the impact of dichotic pulse rates on auditory object formation and ITD lateralization?
Auditory object formation (AOF) in normal-hearing (NH) listeners necessitates a set of grouping cues that provide the perception of a single auditory stream. However, when the stimulus is dichotic, AOF is limited when frequency-specific binaural channels are not matched1.
Components that influence a listener's ability to successfully attend to a signal in noise include:
Results suggest that dichotic rates presented to BiCI listeners can still lead to a fused auditory image. However, this does not necessarily lead to correct lateralization of the stimulus. Such a result would suggest that grouping of mismatched information may not lead to correct lateralization.
Furthermore, pulse rate or pseudo-“pitch” may be a preferred strategy in deciding where the sound is heard for some listeners.
1. Steiger H. and Bregman, A. (1982b). Competition among auditory streaming, dichotic fusion, and diotic fusion. Perception & Psychophysics. 1982, 32(2), 153-162.2. Kan A., and Litovsky RY (2015). Binaural hearing with electrical stimulation. Hear Res. 2015 Apr;322:127-37.3. Carlyon RP., Long CJ., and Deeks JM (2008). Pulse-rate discrimination by cochlear-implant and normal-hearing listeners with and without binaural cues. J Acoust Soc Am. 2008 Apr;123(4):2276-86.4. Krumbholz K., Patterson RD., and Pressnitzer D. (2000). The lower limit of pitch as determined by rate discrimination. J Acoust Soc Am. 2000 Sep;108(3 Pt 1):1170-80.
We would like to thank all our participants and Cochlear Ltdfor providing equipment. A special thank you to RachaelJocewicz for her comments on the poster. This work is fundedby NIH-NIDCD (R01 DC003083 to RYL), and NIH-NICHD (P30HD03352 to Waisman Center).
Left:100 pps & Right: 150 pps (example stimulus)Left:100 pps & Right:100 pps (i.e. matched pulse rates only)
Dichotic pulse rate condition
Figure 1: Example of response options
Figure 2: Stimulus examples for diotic and dichotic pulse-rate conditions.
Listener ID
Age Years of CI experience(Bilateral)
Etiology Electrode Pair #
L R
IBF 59 3 Heredity 12 12
IBK 75 5 Heredity 14 13
IBQ 80 6 Meniere's 14 7
ICJ 66 8 Childhood illness
20 16
IAU 68 12 Heredity (from birth)
12 11
Figure 3: Data from Carlyon et al. (2008): suggests that NH listeners can detect a dichotic F0 difference in
pulse rates as small as 0.4% of 300 pps.
Figure 4: Percentage of ‘One’ sound responses (“One-Left”, “One-Center”, or “One-Right”) across listeners.
Assuming NH listeners can discriminate small rate differences between the ears,
they would exhibit a narrow range of AOF for dichotic rates.
NH listeners’ dichotic pulse-rate discrimination ability: BiCI listeners’ auditory object formation:
BiCI listeners’ ITD lateralization (within all ‘One’ sound responses): Figure 5: Percentage of correctly lateralized ‘One’ sounds, with
individual ITD thresholds labeled on right of the figure.
Compare NH and BiCI populations
ITD thresholds (µs) at 100 pps, dichotic pulse rates:
IBF:~62 µs
IBK: ~52 µs
IBQ: ~264 µs
ICJ: ~203 µs
IAU: ~638 µs
Listeners with good ITD sensitivity showed AOF and lateralization when rates are
interaurally matched.
Listeners with poorer ITD sensitivity showed poor lateralization with dichotic pulse rates even in the presence of AOF.
RESULTS: Perceived lateralization
Response patterns across listeners appear to differ: A) IBK and IBF no longer lateralize the ITD of the perceived
single fused image with the introduction of dichotic pulse rates
B) ICJ, IBQ, IAU, lateralize by making more “left” and “right” decisions in the dichotic pulse-rate conditions.
Figure 6: Percentage of lateralized ‘One’ sound responses per target ITD.
ITD (µs)
ITD (µs)Diotic pulse rate condition
BiCI listeners show a broad range of tolerance for AOF with increasing dichotic pulse rates.
