Binaural Hearing and Speech Laboratory Possible Implications of Interaural Mismatch in the...

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Binaural Hearing and Speech Laboratory Possible Implications of Interaural Mism atch in the Place-of-Stimulation on Spatial Release from Masking in Cochlear Implant Listeners Alan Kan, Corey Stoelb, Matthew Goupell, Ruth Litovsky

Transcript of Binaural Hearing and Speech Laboratory Possible Implications of Interaural Mismatch in the...

Binaural Hearing and Speech Laboratory

Possible Implications of Interaural Mismatch in the Place-of-Stimulation

on Spatial Release from Masking in Cochlear Implant Listeners

Alan Kan, Corey Stoelb, Matthew Goupell, Ruth Litovsky

Binaural Hearing and Speech Laboratory

Cochlear Implants (CI) restore hearing

Source: http://www.cochlear.com/uk/node/6858

Binaural Hearing and Speech Laboratory

Binaural cues tells us where sounds come from

Bang!

Interaural time difference (ITD)

Interaural level difference (ILD)

Binaural Hearing and Speech Laboratory

Spatial Release from Masking (SRM)

The improvement in speech-in-noise understanding gained from a separation

between target and masker sources

TargetMasker

Binaural Hearing and Speech Laboratory

Loizou et. al. (2009)

SRM

(dB)

SRM

(dB)

CI users Normal hearing listeners

Binaural Hearing and Speech Laboratory

Interaural place-of-stimulation mismatch

Base Apex

Left

Right

Electrode # 2 4 6 8 10 12 14 16 18 20 22

2 4 6 8 10 12 14 16 18 20 22Electrode #

20000 Hz 20 Hz7000 Hz 4000 Hz

Binaural Hearing and Speech Laboratory

Mismatch affects SRM

Binaural Hearing and Speech Laboratory

What is the effect of mismatch on sound image fusion?

Base Apex

Left

Right

Electrode # 2 4 6 8 10 12 14 16 18 20 22

2 4 6 8 10 12 14 16 18 20 22Electrode #

20000 Hz 20 Hz

Binaural Hearing and Speech Laboratory

Find a matched pair via pitch matching

Base Apex

Left

Right

Electrode # 2 4 6 8 10 12 14 16 18 20 22

2 4 6 8 10 12 14 16 18 20 22Electrode #

20000 Hz 20 Hz

Δ=0

Binaural Hearing and Speech Laboratory

Mismatch conditions

Base Apex

Left

Right

Electrode # 2 4 6 8 10 12 14 16 18 20 22

2 4 6 8 10 12 14 16 18 20 22Electrode #

20000 Hz 20 Hz

Δ=0

Δ=-2 Δ=-4 Δ=-8Δ=2Δ=4Δ=8

Right higher in frequency Left higher in frequency

1.5 mm

Binaural Hearing and Speech Laboratory

What do you hear?

Binaural Hearing and Speech Laboratory

Mismatch affects where a sound is perceived

Left higher in frequency

Right higher in frequency

Binaural Hearing and Speech Laboratory

Mismatch affects people differently

Left higher in frequency

Right higher in frequency

Left higher in frequency

Right higher in frequency

Binaural Hearing and Speech Laboratory

Increasing mismatch leads to more split sound images

Binaural Hearing and Speech Laboratory

Most people lateralize towards high frequencies

Binaural Hearing and Speech Laboratory

Possible Implications

Target

Lateralized sound image

TargetTarget

Split sound image

Binaural Hearing and Speech Laboratory

How does mismatch affect sounds off the mid-line?

Typical values:•ILD = 0; ±2; ±5; ±10 CU•ITD = 0; ±100; ±200; ±400; ±800 µs•Negative values mean sound is to the left.

Binaural Hearing and Speech Laboratory

Good lateralization at no mismatch

Binaural Hearing and Speech Laboratory

Mismatch affect ILDs

Binaural Hearing and Speech Laboratory

Mismatch affect ILDs

Binaural Hearing and Speech Laboratory

Mismatch affect ITDs even more

Binaural Hearing and Speech Laboratory

Non-midline crossings increase with mismatch

L

C

R

Binaural Hearing and Speech Laboratory

Possible Implications

Lateralized sound image Split sound image

Masker MaskerMasker

Binaural Hearing and Speech Laboratory

Possible implications on SRM

Target

Masker

TargetMaskers

Lateralized Image

Binaural Hearing and Speech Laboratory

Possible implications on SRM

Target

Masker

Target MaskersLateralized Image

TargetMaskers

Lateralized Image

Binaural Hearing and Speech Laboratory

Possible implications on SRM

Target

Masker

TargetMaskersTargetMaskers

Split Image

Target MaskersLateralized Image

TargetMaskers

Lateralized Image

Binaural Hearing and Speech Laboratory

Summary

• Interaural place-of-stimulation mismatch leads to lateralized or split sound images which affects perceived location of sounds

• Depending on location of target and masker, interaural mismatch might increase or hinder spatial release from masking

Binaural Hearing and Speech Laboratory

Thank you

• We’d like to thank our research participants for participating in our experiments, and Cochlear Ltd. for supplying the equipment and technical support.

• This work is supported by NIH-NIDCD R01003083 (Litovsky) and in part by a core grant to the Waisman Center from the NICHD (P30 HD03352).