Hearing assistance device comprising an implantable part

1. A method of operating a hearing assistance device, the hearing assistance device comprising an implantable part, the method comprising:

providing an electrode array comprising one or more stimulation electrodes configured to be located inside one of the cochlear scala or adjacent to the auditory nerve, or at the auditory brainstem of a user of the hearing assistance device;

providing stimulation current to generate electric stimulation pulses to one or more of said stimulation electrodes; and

using said stimulation current to provide a parameterized time-varying waveform of said electric stimulation pulses to one or more of said stimulation electrodes, said parameterized time-varying waveform comprising a positively sloping positive pulse when plotted in terms of amplitude of current versus time, thereby creating auditory sensation for the user of the hearing assistance device, the auditory sensation corresponding to sound from a local environment of the user during normal operation of the hearing assistance device,

wherein said stimulation pulses generated by said one or more stimulation electrodes are shaped as a positively sloping positive pulse when plotted in terms of amplitude of current versus time, according to said parameterized time-varying waveform.

2. A method according to claim 1 comprising providing a model of ionic currents present in a nerve or neuron, from which the temporal pattern of current to deliver can be computed so that a specific discharge probability and/or temporal accuracy can be obtained.

3. A method according to claim 1 comprising one or more of the following steps:

computing a first passage time probability density using a model of said parameterized time-varying waveform,

computing a set of fibres, which are activated by a single pulse of said parameterized time-varying waveform,

computing interactions between sub-sequent pulses in a pulse train of said parameterized time-varying waveforms.

4. A method according to claim 1 comprising modulating the probability of discharging neurons of the cochlear nerve using a parameterized time-varying waveform specifically designed to limit the spread of excitation.

5. A method according to claim 1 comprising modulating the parameterized time-varying waveform by acting on either the spread of excitation or the discharge probability or the discharge latency.

6. A method according to claim 1 comprising a fitting procedure wherein the patient estimates the extent of the spread of excitation a specific electric stimulation pulse.

7. A method according to claim 1 comprising a fitting procedure, wherein a subjective measure related to the use of a masking paradigm is provided in which the patient is asked to detect the presence of a target stimulation in concurrence with a masker presented simultaneously or earlier.

8. A method according to claim 1 comprising a fitting procedure, wherein an objective measure for fitting the pulse-shape is provided, said objective measure being based on recording the nerve response after its stimulation or any evoked neural response produced by the stimulation.

9. A data processing system comprising a processor and program code means for causing the processor to perform the steps of the method of claim 1 .

10. A fitting system configured to estimate the extent of the spread of excitation of different parameterized time-varying waveforms according to the method of operating a hearing assistance device defined in claim 6 .