Multichannel cochlear prosthesis with flexible control of stimulus waveforms

Abstract

A cochlear implant system includes an implant portion and an external portion. The external portion performs at least the function of sensing acoustic signals and converting such sensed signals to electrical signals. The implant portion performs at least the function of generating electrical stimuli, modulated and classified in response to the sensed acoustic signals, and intended for direct electrical stimulation of the auditory nerve in accordance with a selected speech processing strategy. Control data defines the selected speech processing strategy, i.e., the pulsatile stimulation pattern to be used by implantable portion. Such control data is transmitted to and stored within the implantable portion of the system only once, when a particular speech processing strategy is selected, thereby eliminating the need to continually resend such speech-processing-defining data over a bandwidth-limited link between the implantable and external portions of the system. The control data that defines the selected speech processing strategy is stored in a stimulation template (also referred to as a “pulse table”), which template or table is stored digitally within the implanted portion of the system. Weighting coefficients (or weighting factors) are stored in the template or table at specified locations to define the speech processing strategy. For example, the columns of the template or table may be used to represent the different current sources, or “stimulous channels”, of the implanted portion, and the rows may be used to represent intervals of time. The “stimulous channels” and increments of time thus form the two ordinates of the table, and the table thus consists of a modest number of intervals whose total duration defines a complete “cycle” of stimulation. The instantaneous current flow to be generated by the implanted portion is defined at the beginning of each stimulation cycle by multiplying the weighting factor stored in a particular location within the pulse table by modulation data derived from the sensed acoustic signal. Only modulation data need be sent to the implanted portion on a continuous (real time) basis for the cochlear implant system to function.