The purpose of this project is to describe the ensemble of afferent neural responses to intracochlear electrical stimulation as a function of stimulation variables. Several types of ensemble models will be investigated, including combinations of the various field and neural models from Projects II and III and the addition of stochastic properties to such combined models. Each ensemble model will predict both the spatial and temporal patterns of neural excitation. Conditions will include manipulations in (a) electrode coupling configuration [e.g., monopolar, radial bipolar, longitudinal bipolar], (b) stimulus waveform [e.g., sinusoidal, pulsatile], and (c) the number and geometry of electrode pairs in multichannel electrode arrays. Predictions from models spanning these conditions will test our understanding of the mechanisms underlying psychophysical and behavioral findings with respect to threshold, dynamic range, intensity discrimination, frequency discrimination, channel interactions, and channel discrimination. These predictions will be evaluated directly within this project using single-unit experiments. Such evaluations will, in turn, allow further refinement of the ensemble models and their constituent parts. Iterations of this model/test cycle will periodically refocus or efforts toward key gaps in existing knowledge.
