Forward masked excitation patterns in multielectrode electrical stimulation

Across-channel interactions in multi-electrode cochlear implant patients may be critical to their performance in the natural auditory environment. One measure of channel interaction can be obtained using forward masking. The patterns of threshold shift were obtained as a function of the separation between masker and probe electrode pairs in four Nucleus-implanted patients with varying levels of speech recognition. In the three subjects with better speech recognition (N4, N7, and N13), the masking patterns showed the least parameter dependence. In the subject with the lowest speech scores (N3), the masking patterns showed the greatest dependence on masker level and on probe delay. Masking as a function of masker level also reflected these differences: N3's functions showed the greatest changes for different probe delays. Similar rates of recovery were observed in the three good performers (time constant approximately 70 ms). In contrast, subject N3's recovery function shows a more rapid recovery. These data indicate that channel interaction is individually variable and parameter dependent, both of which may play a role in the perception of dynamic stimuli in the natural auditory environment.