Effect of current level on electrode discrimination in electrical stimulation

The effect of the stimulation intensity (current amplitude) on the ability to discriminate electrodes was tested in an experiment with four adult user s of the Nucleus-22 cochlear implant. A total of 12 adjacent pairs of elect rodes were used in the four-interval forced-choice discrimination task with random current variation. Tests were carried out at three average stimulat ion levels: 40 and 70% of the dynamic range and close to maximum comfortabl e loudness. Analysis of variance revealed a significant (P<0.0001) deterior ation in electrode discrimination with a decreasing level. However, the ove rall effect was very small, representing a deterioration in the discriminat ion score of only 18% correct from the highest to lowest levels tested. The reason for the small deterioration in discriminability with a decreasing l evel is difficult to determine from this experiment, however, the results a re consistent with the hypothesis that changes in the 'peak' or 'edge' of t he excitation pattern are more important for discrimination tasks than the relative amount of non-overlap of the excitation areas from the two electro des. (C) 1999 Elsevier Science B.V. All rights reserved.