Estimation of the Effective Spread of Neural Excitation Produced by a Bipolar Pair of Scala Tympani Electrodes

Psychophysical studies were conducted on two multichannel cochlear implant patients for electrical stimulation of two bipolar electrode pairs in the human cochlea. Loudness summation was approximately complete for spatial separation of about 3 mm between the two electrode pairs. At comfortable loudness, the effective spread of neural excitation produced by a bipolar pair of scala tympani electrodes was estimated to be 3 to 4 mm on the basis of both loudness summation and forward masking results.