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?

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

Listening to speech in quiet with reduced frequency resolution

Resolution: Intelligibility vs. number of electrodes Simulation for normal hearing Implant users Friesen et al., JASA v110, , 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

Spectral resolution: speech in noise

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 quiet 60% with competing speech at +10 dB SNR Absolute performance in both groups likely limited by the task – but both groups are significantly affected by noise that is trivial for normal hearing adults Speech recognition by 2 year children

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

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

Sound localisation and Speech in Noise: Results from Rosie Lovett (UCL Ear Institute) with Pádraig Kitterick and Quentin Summerfield (York ) Participants Unilateral implant Bilateral implants Normal hearing N Age Listening age Lovett, Kitterick, Hewitt, & Summerfield (2010). Bilateral or unilateral cochlear implantation for deaf children: an observational study. Archives of Disease in Childhood, 95,

Five-alternative localisation

5-alternative localisation Chance 30° Unilateral Bilateral Normally hearing

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

Spatial release from masking Noise opposite to 1st CI compared to noise from the front Unilateral Bilateral Normal hearing 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”

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

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

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 all implanted before age 3 Only 3 of the 17 show similar pitch perception to age-matched normal-hearing children

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

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

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

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

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