ASA 125th Meeting Ottawa 1993 May

3aPP10. Forward masking patterns and pitch estimation for bipolar and remote ground stimulation in a subject implanted with a Cochlear Pty. Limited ``20+2'' cochlear implant.

Lawrence T. Cohen

Dept. of Otolaryngol., Univ. of Melbourne, Parkville 3052, Australia

Graeme M. Clark

Lesley Whitford

Univ. of Melbourne, Parkville 3052, Australia

A new electrode array, recently developed by Cochlear Pty. Limited, enables ``remote ground'' as well as standard bipolar stimulation. To compare the patterns of electrical stimulation for these two operating modes, forward masking and pitch estimation investigations were performed with a single patient. The masking patterns were studied using a bipolar+1 or a remote ground masker, followed by a bipolar+1 probe. For maskers on apical and middle electrodes, masking patterns were more apical for bipolar +1 than for remote ground maskers, while for maskers on a basal electrode, masking was similar for the two masker modes. For a bipolar+1 masker on a middle electrode, masking was skewed strongly toward the apical end of the array. In the apical half of the array, while remote ground pitch reduced regularly with movement apically, bipolar+1 pitch dropped abruptly to a constant low value for the nine most apical electrodes and was lower than remote ground pitch for each electrode. The results show that remote ground stimulation may provide a different, and at least for this patient a better, range of pitch percepts, as well as other benefits such as reduced current requirement. [Work supported by NIH.]