The invention relates to apparatus and methods for stimulating living tissues to determine nerve conduction properties using a pair of stimulator probes and a plurality of detection electrodes. The invention overcomes the problem of reporting potentially inaccurate nerve conduction results by detecting a stimulator probe short or shunt condition during nerve conduction tests. Detection of a short or shunt condition between two stimulator probes is accomplished by monitoring the magnitude of the stimulus artifact waveform acquired from the detection electrodes and the voltage difference between the stimulator probes. A test is flagged when magnitude of the stimulus artifact waveform is below a first threshold and voltage difference between the two stimulator probes is below a second threshold. The first and second threshold values are determined based on the known spatial relationship between the stimulator probes and detection electrodes. Feedback is provided to the tester to alert defective test conditions.