Re: Cochlear implants and pitch. (Bob Carlyon )

Subject: Re: Cochlear implants and pitch.
From:    Bob Carlyon  <bob.carlyon(at)MRC-CBU.CAM.AC.UK>
Date:    Tue, 27 Nov 2001 17:56:42 +0000

hi folks,

There is some evidence at least that subjects hear a single pitch
(Townshend et al, 1987, JASA 82, p106-115). When pulsatile stimulation is
used, with pulses on the two electrodes nearly simultaneous (differing by
0.4 ms), then, provided the electrodes are quite close (<3 mm) one can vary
the pitch monotonically by varying the relative current on the two
electrodes (McDermott & McKay, 1994,JASA 96 p155-162)

I suspect that at very wide electrode separations this would break down.
Certainly, the temporal pitch pattern that listeners hear as a result of
two interleaved patterns of stimulation on 2 electrode pairs, differs as a
function of the electrode separation (at small separations they hear the
"composite" pattern; at wide separations they do not; McKay & McDermott,
1996, JASA 100 p1081-1092)

I'd also think that a better analogy in normal hearing would be two narrow
bands of noise (or bandpass filtered pulse trains) with different centre
frequencies

cheers

bob