The present invention relates to programming of a speech processor for use with an implantable cochlear stimulator, and more particularly to a method and apparatus for fitting a speech processor and implantable cochlear stimulator by programming the speech processor. Even more particularly, the present invention relates to fitting the speech processor and implantable cochlear stimulator to a particular patient by programming the speech processor with a threshold stimulation level and a comfortable stimulation level, by programming an input dynamic range, and by programming a gain level.
Electrical stimulation of predetermined locations within the cochlea of the human ear through an intra-cochlear electrode array is described in U.S. Pat. No. 4,400,590. The electrode array shown comprises a plurality of exposed electrode pairs spaced along and imbedded in a resilient curved base for implantation in accordance with a method of surgical implantation described in U.S. Pat. No. 3,751,615. The system described in the '590 patent receives audio signals, i.e., sound waves, at a signal processor (or speech processor) located outside the body of a hearing impaired patient. The speech processor converts the received audio signals into modulated RF data signals that are transmitted by a cable connection through the patient's skin to an implanted multi-channel intracochlear electrode array. The modulated RF signals are demodulated into analog signals and are applied to selected ones of the plurality of exposed electrode pairs in the intra-cochlear electrode so as to electrically stimulate predetermined locations of the auditory nerve within the cochlea.
U.S. Pat. No. 4,532,930 describes a multiple electrode stimulation system wherein only a single pulsatile output stimulates a single electrode channel at a given time. The single pulsatile output is generated on each of several electrodes in a sequential fashion, which unfortunately limits speed of operation and does not provide for analog operation wherein continuous stimulating signals of controllable amplitude are simultaneously applied to a number of electrode channels. Once a stimulator unit is implanted in a patient, there may only be limited means for monitoring ongoing circuit operation, e.g., selected parameters that are telemetered back to the external signal processor, or no means at all, in which case the circuit operation or power requirements of the unit cannot be monitored, or cannot be easily monitored, so as to optimize its continued operation.
U.S. Pat. No. 4,592,359 describes a cochlear implant system employing four current sources and four current sinks per channel. The four current sources and four current sinks are controlled by series switches to provide 16 indifferent circuits for applying 16 levels of two polarities to each output channel. In a pulsatile mode, the system provides for simultaneous update (amplitude control) and output to all channels. However, the system does not permit simultaneous analog update and output on all channels, and the electrode pairs for each channel are not electrically isolated from all other electrode pairs, creating the risk that undesired current leakage may occur. Once the stimulator is implanted, there is no means for monitoring its ongoing circuit operation or power requirements.
U.S. Pat. No. 4,947,844 shows a multiple channel electrode system, including an implanted receiver/stimulator connected to an implanted electrode array. The receiver/stimulator includes an electrode stimulating current control characterized in that current is delivered to each electrode or to each bipolar pair of electrodes in a series of short electrical pulses. Each elemental pulse is separated from the next by an interval of zero current, which has a longer duration than each elemental pulse. The waveform of the stimulus current comprises a series of pulses of one polarity followed by an equal number of pulses of another polarity whereby the sum of all electrical charge transferred through each electrode is approximately zero at the end of a stimulating current waveform. Simultaneous operation of the output channels is not possible and the number of channels cannot be greater than three or four without greatly reducing the duty cycle of the stimulating current waveform in each channel.
U.S. patent application Ser. No. 08/023,584, filed Feb. 26, 1993, of Schulman, et al., and incorporated herein by reference, shows an improved multi-channel cochlear stimulation system employing an implanted cochlear stimulator (ICS) and an externally wearable speech processor (SP). The speech processor employs a headpiece that is placed adjacent to the ear of the patient, which receives audio signals and transmits the audio signals back to the speech processor. The speech processor receives and processes the audio signals and generates data indicative of the audio signals for transcutaneous transmission to the implantable cochlear stimulator. The implantable cochlear stimulator receives the transmission from the speech processor and applies stimulation signals to a plurality of cochlea stimulating channels, each having a pair of electrodes in an electrode array associated therewith. Each of the cochlea stimulating channels uses a capacitor to couple the electrodes of the electrode array. (The ICS and SP disclosed in the referenced Schulman, et al. patent application is manufactuered and sold by the assignee of the present application under an exclusive license.)
The implantable cochlear stimulator is responsive to control signals from the speech processor and selectively monitors one or more of the electrodes, and voltages within the processor, in order to generate an implantable cochlear stimulator status indicating signal. The status indicating signal can be telemetered back to the speech processor, which, for example, may use the status indicating signal to control the power level of transmissions to the implantable cochlear stimulator.
The implantable cochlear stimulator described in the '065 application is also able to selectively control the pulse width of stimulating pulses that are applied through the electrode array to the cochlea, and the frequency at which the stimulating pulses are applied.
Thus, as the art of cochlear stimulation has advanced, both the implanted portion of the cochlear stimulation system, and the externally wearable processor (or speech processor) have become increasingly complicated and sophisticated. The amount of control and discretion exercisable by an audiologist in selecting the modes and methods of operation of the cochlear stimulation system have increased dramatically and it is no longer possible to fully control and customize the operation of the cochlear stimulation system through the use of, for example, switches located on the speech processor. As a result, it has become necessary to utilize an implantable cochlear stimulator fitting system to establish the operating modes and methods of the cochlear stimulation system and then to download such programming into the speech processor.
Unfortunately, currently available systems for programming (or fitting) of cochlear stimulation systems, while providing a degree of flexibility in the programming of the modes and methods of operation of the cochlear stimulation system, lack the ability to automate such procedures by establishing such modes and methods of operation based solely or in part of objective measurements taken from the patient.
The need for such a system becomes increasingly important as the ages of patients into which implantable cochlear stimulators are implanted decreases. This is because very young patients, for example, two year olds, are unable to provide adequate subjective feedback to the audiologist for the audiologist to accurately "fit" the cochlear stimulation system optimally for the patient. Furthermore, currently available programming units do not provide a level of feedback to the audiologist that enables the audiologist to independently evaluate the stimulation being applied to the patient, and thereby optimize such stimulation without guidance or with little guidance from the patient. Thus, what is needed is an improved apparatus and method for programming a speech processor of a cochlear stimulation system that provides for the utilization of objective measurements in the setting of the modes and methods of operation of the cochlear stimulation system, and further provides a mechanism of objective feedback to the audiologist so the audiologist can evaluate the stimulation being applied to the patient.