Melbourne piano teacher Daniela Andrews (Blog | Facebook) accidentally leveled a Very Damning Indictment of her simultaneously implanted Nucleus 5 CI’s, where she points out a major flaw in Cochlears’ design, with its’ 22 electrodes spaced too close together for its’ 22 hardware channels: This causes Channel Crossover, which Daniela unintentionally — Yet so eloquently — described. If you remember back in February, there was the special Interior Design Concert by the Bionic Ear Institute for people with CI’s. Daniela, as a music professional, was one person involved with it; so you know she has the “street creds.”
At some point after she was implanted, she wrote the following that was picked up in the Australia Hears blog under Listening to music with a hearing loss. I copied & pasted it below; with my notes [blue, in brackets]:
3. Playing music
There is not a large amount of research investigating whether playing music can help with re-training the brain after a hearing loss. However there are some personal stories we can share. Daniela Andrews lost her hearing around 4 years ago, and for the last 10 months [implanted April 2010] has bilateral cochlear implants:
“At first, the piano sounded terrible. Like somebody had broken into it while I was in surgery and mixed up all the notes for fun. Playing scales barely resembled an up and down pattern at all. [This is channel crossover, caused by the electrodes being spaced too close together, stimulating the wrong nerve endings in the spiral ganglion] There were random low tones in between higher ones, and vice versa. Being simultaneously implanted brought another challenge – each processor rendered two different tones for the same note. [This is diplacusis — the same tone sounding different in each ear — which is exacerbated by the randomness caused by the channel crossover.] Familiar songs sounded alien-like with all these extra wrong notes thrown in. How was my brain ever going to make sense of that mess?”
Technically, each channel could have been remapped to produce a chromatic scale; but that would be painstaking and time consuming… And according to feedback from several CI manufacturer insiders, is above the skill level of many CI audies.
There are two parts to the solution for better music enjoyment:
- Wider electrode spacing, to stop the crossover;
- Current steering (think of a spotlight, instead of a floodlight), to shape the charge distribution, which will fill in the gaps between the electrodes.
Of the four CI manufacturers, Advanced Bionics uses 16 electrode contacts spaced out over 21mm; Neurelec (not available in the USA) uses 12 electrodes spaced out over 23mm; while MedEl uses 12 electrodes spaced over 31.6mm. In addition, both AB (Fidelity 120) and MedEl (FineHearing) have current steering, for much better music performance (though AB has severe implant reliability problems, with five recalls in the last decade).
There are many factors that go into choosing a CI, as indeed there are differences in performance, as well as ergonomics and reliability. We recommend treating the issue of channel crossover as one data point in your decision matrix.