Abstract: The behavioral tendencies of a system in which responses evoked by stimuli are measurable are determined by means of a method and apparatus for applying a train of paired stimuli to the system and measuring and analyzing the response. The first of each pair of stimuli (conditioning stimulus) is applied at randomly varying intensities and at a constant interval. The second of each pair of stimuli (test stimulus) is applied at a constant intensity and a randomly varying interval from its associated test stimulus. By appropriate analysis of the amplitude and latency of the evoked responses, important information about fatigue, refractory period, supernormal period, threshold and dynamical fluctuation can be determined.