an implantable device for estimating neural recruitment arising from a stimulus , has a plurality of electrodes . a stimulus source provides stimuli to be delivered from the electrodes to neural tissue . measurement circuitry obtains a measurement of a neural signal sensed at the electrodes . a control unit is configured to control application of a selected stimulus to neural tissue using the stimulus electrodes ; and after the selected neural stimulus , apply a probe stimulus having a short pulse width . a remnant neural response evoked by the probe stimulus is measured ; and the control unit estimates from the remnant neural response a neural recruitment caused by the selected neural stimulus .