Wonder if the same "type" of people work both computers and CIs?
A processor is a mini-computer, after all.
A lot of people working with CIs have degrees in EE (electrical engineering), which is often in the same department as CS (computer science). Some universities offer both as one major, the rationale being that if you are an expert in one, you should know at least the basics of the other.
The signal processing that hearing aids and CIs do involves a lot of CS and math, too - as SR171 said, fast fourier transforms (Fourier transforms have to do with creating mathematical models for waves, including sound waves), voice recognition, and so on.
Combination EECS and bio degrees are becoming relatively popular with engineering majors, because the two intersect quite a bit - as in this example.