The study is concerned with the problem of determining stimulus discrimination thresholds in non-human vertebrates. In constrast to conventional methods of teaching differentiation of various stimuli by fixed reinforcement schedules, stimulus discrimination threshold determination is related to a teaching system that adjusts to continuously varying performance criteria. In order to develop and construct such a teaching system, an analysis and synthesis of the minimal structural and functional properties of a discriminatory system has been carried out. In the synthesis it is shown that a heterarchical rather than a hierarchical regulatory structure fulfills these requirements. This accomplished, a model of a learning teaching system was developed, and a machine based on this model was designed and built. (Author)