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Alan Kan , Corey Stoelb , Matthew Goupell , Ruth Litovsky

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. Cochlear Implants (CI) restore hearing. Source: http://www.cochlear.com/uk/node/6858.

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Alan Kan , Corey Stoelb , Matthew Goupell , Ruth Litovsky

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  1. Possible Implications of InterauralMismatch in the Place-of-Stimulationon Spatial Release from Masking in Cochlear Implant Listeners Alan Kan, Corey Stoelb, Matthew Goupell, Ruth Litovsky

  2. Cochlear Implants (CI) restore hearing Source: http://www.cochlear.com/uk/node/6858

  3. Binaural cues tells us where sounds come from Interaural time difference (ITD) Bang! Interaural level difference (ILD)

  4. Spatial Release from Masking (SRM) The improvement in speech-in-noise understanding gained from a separation between target and masker sources Target Masker

  5. CI users Normal hearing listeners SRM (dB) SRM (dB) Loizou et. al. (2009)

  6. Interaural place-of-stimulation mismatch Base Apex Electrode # 2 4 6 8 10 12 14 16 18 20 22 Left Electrode # 2 4 6 8 10 12 14 16 18 20 22 Right 20000 Hz 7000 Hz 4000 Hz 20 Hz

  7. Mismatch affects SRM

  8. What is the effect of mismatch on sound image fusion? Base Apex Electrode # 2 4 6 8 10 12 14 16 18 20 22 Left Electrode # 2 4 6 8 10 12 14 16 18 20 22 Right 20000 Hz 20 Hz

  9. Find a matched pair via pitch matching Base Apex Electrode # 2 4 6 8 10 12 14 16 18 20 22 Left Electrode # 2 4 6 8 10 12 14 16 18 20 22 Right 20000 Hz 20 Hz Δ=0

  10. Mismatch conditions 1.5 mm Base Apex Electrode # 2 4 6 8 10 12 14 16 18 20 22 Left Electrode # 2 4 6 8 10 12 14 16 18 20 22 Right 20000 Hz 20 Hz Δ=8 Δ=4 Δ=2 Δ=-2 Δ=-4 Δ=-8 Left higher in frequency Right higher in frequency Δ=0

  11. What do you hear?

  12. Mismatch affects where a sound is perceived Left higher in frequency Right higher in frequency

  13. Mismatch affects people differently Left higher in frequency Left higher in frequency Right higher in frequency Right higher in frequency

  14. Increasing mismatch leads to more split sound images

  15. Most people lateralize towards high frequencies

  16. Possible Implications Target Target Target Split sound image Lateralized sound image

  17. 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.

  18. Good lateralization at no mismatch

  19. Mismatch affect ILDs

  20. Mismatch affect ILDs

  21. Mismatch affect ITDs even more

  22. Non-midline crossings increase with mismatch L C R

  23. Possible Implications Masker Masker Masker Split sound image Lateralized sound image

  24. Possible implications on SRM Lateralized Image Target Target Masker Maskers

  25. Possible implications on SRM Lateralized Image Lateralized Image Target Target Masker Maskers Target Maskers

  26. Possible implications on SRM Lateralized Image Lateralized Image Maskers Maskers Target Target Target Target Masker Maskers Target Maskers Split Image

  27. 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

  28. 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).

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