Method and apparatus for estimating neural recruitment

An implantable device for estimating neural recruitment arising from a selected neural stimulus, the device comprising:

• a plurality of electrodes including one or more nominal stimulus electrodes and one or more nominal sense electrodes;
• a stimulus source for providing stimuli to be delivered from the one or more stimulus electrodes to neural tissue;
• measurement circuitry for obtaining a measurement of a neural signal sensed at the one or more sense electrodes;
• and
• a control unit configured to control application of a selected stimulus to neural tissue using the stimulus electrodes;
• the control unit further configured to, after the selected neural stimulus, apply a probe stimulus having a short pulse width;
• the control unit further configured to measure a remnant neural response evoked by the probe stimulus;
• and the control unit further configured to estimate from the remnant neural response a neural recruitment caused by the selected neural stimulus.