A hearing prosthesis, comprising: a microphone; a sound processor; an external transmitter unit including a coil; an internal receiver unit including a coil; a stimulator unit, wherein the stimulator unit includes a control circuit, a voltage measurement component, a resistor and a signal generator, wherein the measurement circuit is configured to output a signal indicative of the voltage across the resistor; and a stimulating lead assembly array, wherein at least a portion of the hearing prosthesis is configured to apply an electrical signal to tissue inside a cochlea of a recipient, and at least a portion of the hearing prosthesis is configured to sense an electrical property inside of the cochlea that results from the applied electrical signal and the interaction of the applied electrical signal to the tissue.