Absolute identification of electric pulse rates and electrode positions by cochlear implant patients

In a single interval task, multichannel cochlear implant patients were asked to identify the members of a set of seven electric stimuli differing in electric pulse rate or electrode position. The perceptual sensitivity index (d') between successive stimuli in a stimulus set was calculated from the confusions among the seven stimuli. The results showed that the pulse rate above which the identification task became difficult varied from 200 to 600 pps from patient to patient. For the identification of the positions of seven bipolar electrode pairs, d' measures for stimulus sets differing in spatial separation or spatial extent were compared. Spatial separation is defined as the fixed distance between the two basal (or apical) electrodes of two successive bipolar electrode pairs in a stimulus set, while spatial extent is defined as the fixed distance between the apical and basal electrodes of each bipolar electrode pair in a stimulus set. The results showed that perceptual performance improved in an orderly way with spatial separation, but was not significantly affected by spatial extent.