A system , comprising: an implantable medical device comprising an intra-cochlea electrode and a plurality of spatially separated intra-cochlea electrodes , and a signal processor configured to perform a method comprising the following steps: applying electrical current to the intra-cochlea electrode , wherein the electrical current is insufficient to evoke a hearing percept in a recipient of the implantable medical device; measuring a voltage induced by the applied electrical current at a plurality of spatially separated intra-cochlea electrodes, the measured voltage being indicative of current flowing along a spiral path of the cochlea; and determining a spatial derivative of the measured voltage within the cochlea of the recipient, characterized in that the plurality of spatially separated intra-cochlea electrodes comprises a first group of electrodes disposed basally to the intra-cochlea electrode which electrical current is applied to, and a second group of electrodes disposed apically to the intra-cochlea electrode which electrical current is applied to, wherein the method further comprises the steps of: determining a first spatial derivative of the measured voltage for the first group of electrodes, determining a second spatial derivative of the measured voltage for the second group of electrodes, and comparing the first spatial derivative to the second spatial derivative. an implantable medical device comprising an intra-cochlea electrode and a plurality of spatially separated intra-cochlea electrodes , and a signal processor configured to perform a method comprising the following steps: applying electrical current to the intra-cochlea electrode , wherein the electrical current is insufficient to evoke a hearing percept in a recipient of the implantable medical device; measuring a voltage induced by the applied electrical current at a plurality of spatially separated intra-cochlea electrodes, the measured voltage being indicative of current flowing along a spiral path of the cochlea; and determining a spatial derivative of the measured voltage within the cochlea of the recipient, applying electrical current to the intra-cochlea electrode , wherein the electrical current is insufficient to evoke a hearing percept in a recipient of the implantable medical device; measuring a voltage induced by the applied electrical current at a plurality of spatially separated intra-cochlea electrodes, the measured voltage being indicative of current flowing along a spiral path of the cochlea; and determining a spatial derivative of the measured voltage within the cochlea of the recipient, characterized in that the plurality of spatially separated intra-cochlea electrodes comprises a first group of electrodes disposed basally to the intra-cochlea electrode which electrical current is applied to, and a second group of electrodes disposed apically to the intra-cochlea electrode which electrical current is applied to, wherein the method further comprises the steps of: determining a first spatial derivative of the measured voltage for the first group of electrodes, determining a second spatial derivative of the measured voltage for the second group of electrodes, and comparing the first spatial derivative to the second spatial derivative. determining a first spatial derivative of the measured voltage for the first group of electrodes, determining a second spatial derivative of the measured voltage for the second group of electrodes, and comparing the first spatial derivative to the second spatial derivative. <EOS>