levels. Isolated higher-level control processes can be investigated, but models of an extensive hierarchy of control are still only conceptual, or at best rudimentary. Perceptual control theory has not been widely accepted in mainstream psychology, but has been effectively used in a considerable range of domains in human factors, clinical psychology, and psychotherapy (the "Method of Levels"), it is the basis for a considerable body of research in sociology, and it has formed the conceptual foundation for the reference model used by a succession of NATO research study groups. It is being taught in several universities worldwide and is the subject of a number of PhD dissertations. Recent approaches use principles of perceptual control theory to provide new algorithmic foundations for artificial intelligence and machine learning. Selected bibliography Cziko, Gary (1995). Without miracles: Universal selection theory and the second Darwinian revolution. Cambridge, MA: MIT Press (A Bradford Book). Cziko, Gary (2000). The things we do: Using the lessons of Bernard and Darwin to understand the what, how, and why of our behavior. Cambridge, MA: MIT Press (A Bradford Book). Forssell, Dag (Ed.), 2016. Perceptual Control Theory, An Overview of the Third Grand Theory in Psychology: Introductions, Readings, and Resources. Hayward, CA: Living Control Systems Publishing. . Mansell, Warren (Ed.), (2020). The Interdisciplinary Handbook of Perceptual Control Theory: Living Control Systems IV. Cambridge: Academic Press. . Marken, Richard S. (1992) Mind readings: Experimental studies of purpose. Benchmark Publications: New Canaan, CT. Marken, Richard S. (2002) More mind readings: Methods and models in the study of purpose. Chapel Hill, NC: New View. Plooij, F. X. (1984). The behavioral development of free-living chimpanzee babies and infants. Norwood, N.J.: Ablex. Plooij, F. X. (2003). "The trilogy of mind". In M. Heimann (Ed.), Regression periods in human infancy (pp. 185–205). Mahwah, NJ: Erlbaum. Powers, William T. (1973). Behavior: The control of perception. Chicago: Aldine de Gruyter. . [2nd exp. ed. = Powers (2005)]. Powers, William T. (1989). Living control systems. [Selected papers 1960–1988.] New Canaan, CT: Benchmark Publications. . Powers, William T. (1992). Living control systems II. [Selected papers 1959–1990.] New Canaan, CT: Benchmark Publications. Powers, William T. (1998). Making sense of behavior: The meaning of control. New Canaan, CT: Benchmark Publications. . Powers, William T. (2005). Behavior: The control of perception. New Canaan: Benchmark Publications. . [2nd exp. ed. of Powers (1973). Chinese tr. (2004) Guongdong Higher Learning Education Press, Guangzhou, China. .] Powers,