Investigations towards an artificial cochlea.

Two versions of multichannel cochlear stimulators have been implanted, one allowing stimulation against a common distributed ground within the cochlea and the other allowing bipolar stimulation. The results obtained indicate that with both versions sufficiently discrete stimulation of the auditory nerve is possible in order to be able to make use of tonotopy for the processing of speech. The bipolar stimulation, however, besides of being characterized by higher thresholds than unipolar stimulation, also leads to a very narrow range of stimulus frequency within which perceived pitch is influenced by stimulus frequency. Surprisingly different psychophysical behaviours are exhibited by the two subjects considered, one being a case of prelingual, the other of acquired deafness. This indicates the marked influence which etiology of deafness might have on design considerations for auditory prostheses.