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What can we expect of cochlear implants for listening to speech in noisy environments ?

What can we expect of cochlear implants for listening to speech in noisy environments ?. Andrew Faulkner: UCL Speech Hearing and Phonetic Sciences. What does a cochlear implant do?.

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What can we expect of cochlear implants for listening to speech in noisy environments ?

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  1. What can we expect of cochlear implants for listening to speech in noisy environments? Andrew Faulkner: UCL Speech Hearing and Phonetic Sciences

  2. What does a cochlear implant do?

  3. Time varying spectral shape of speech represented by varying current levels and their distribution along the cochlea Band 1 Band 2 Band 3 Band 4 0.5 1 2 4 kHz

  4. The electrode array • Resolution of spectral patterns (energy by frequency) depends on • the number of electrodes • AND also on their ability to stimulate distinct fibres of the auditory nerve • The degree of spectral resolution patterns is usually much lower than the number of electrodes

  5. Listening to speech in quiet with reduced frequency resolution 1 2 4 8 16

  6. Resolution: Intelligibility vs. number of electrodes Simulation for normal hearing Implant users • Friesen et al., JASA v110, 1150-1163, 2001 • Nucleus-22 patients in Friesen et al. study seem unable to use more than ~ 8 channels • Limited spectral resolution is major problem in noise

  7. Spectral resolution: speech in noise

  8. Speech recognition by 2 year children Greico-Calub et al, 2009 “Word recognition in toddlers who use CIs”.Look at the baby/doggie?Look at the ball/shoe? Gaze direction in 2 yr old CI children shows:70% correct in quiet60% with competing speech at +10 dB SNRAbsolute performance in both groups likely limited by the task – but both groups are significantly affected by noise that is trivial for normal hearing adults

  9. Listening to speech in noiseand with competing speech: Stuart Rosen, UCL Children’s Coordinate Response Measure Pick the colour for the dog

  10. The ability to ignore another talker improves markedly with age in normal hearing children:  better performance

  11. Sound localisation and Speech in Noise:Results from Rosie Lovett (UCL Ear Institute) with PádraigKitterickand Quentin Summerfield (York) Lovett, Kitterick, Hewitt, & Summerfield (2010). Bilateral or unilateral cochlear implantation for deaf children: an observational study. Archives of Disease in Childhood, 95, 107-112.

  12. Five-alternative localisation

  13. 5-alternative localisation 30° Chance Unilateral Bilateral Normally hearing

  14. Speech perception in noise • 14-alternative speech discrimination task • Speech presented from the front Speech and noise Speech Speech Noise Noise

  15. Spatial release from maskingNoise opposite to 1st CI compared to noise from the front Even with just one implant, it helps for the noise to come from side opposite This is because some of the noise is blocked out by the head “shadow” Unilateral Bilateral Normal hearing

  16. Spatial release from maskingNoise on same side as 1st CI compared to noise from front When noise is from side of 1st implant, unilateral listening shows no release from masking Bilateral CI group shows positive masking release although small compared to normal hearing group Unilateral Bilateral Normal hearing

  17. Perception of speech melody: The pitch or melody of speech • signals important words • helps us hear one talker against a background of other speech • crucial in tone languages

  18. Children with CIs are often poor at hearing the changes in the pitch of speech PhD work: Rosemary O’Halpin (UCL) and Ritva Torppa (Helsinki) 17 Finnish children aged 4-12 all implanted before age 3 Only 3 of the 17 show similar pitch perception to age-matched normal-hearing children

  19. Pitch discrimination can be much improved through music-based training Case study of one 7 yr old receiving singing training (Torppa)

  20. Importance of visual cues from speech reading Visual cues can supplement missing acoustic detail (lip shape, tongue position etc.) Visual cues can signal WHEN to listen in noise

  21. You hear a woman saying one sentences in a background of quieter male speech. First the sound is from a 12 channel CI simulation, with and then without speechreading – finally you hear the original speech

  22. Conclusions • Listening to speech in noise is challenging for all children but especially for those with CIs • Children develop the ability to ignore competing talkers and don’t reach adult-like ability until adolescence • Bilateral CIs clearly help localize the direction of sound. • Bilateral CIs give some help hearing speech when noise comes from another direction, but this benefit is small compared to normal hearing • Pitch changes are hard for many CI children to hear. However some do very well, and it seems that good pitch hearing can be trained. • Given the lack of spectral detail with a CI, visual cues are important in supporting communication, especially in noise

  23. Acknowledgements Stuart Rosen, Rosie Lovett, Ritva Torppa for use of their results in this talk For financial support of our research

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