Percepts from scala tympani stimulation.

The characteristics of the sensations produced by activating one electrode at a time are summarized as follows: (a) Loudness was found to increase with current level and pitch with repetition rate. (b) Pitch and sharpness increased in the apical-to-basal direction, and vowel labels could be assigned to sensations produced by individual electrodes in accordance with the tonotopical organization of the cochlea. (c) Results from triadic comparisons provided evidence that the sensations produced by repetition rate and electrode position are perceptually separable. (d) For short-duration stimuli, the discrimination performance for electrode trajectories was much better than that for repetition rate trajectories. For noncoincidental two-electrode stimulation, triadic comparisons showed that two perceptual components, one related to the more basal electrode and the other to the more apical one, could be discerned. Speech-coding considerations based on these psychophysical results are discussed.