Concerns controversies about sensory feedback which have contributed to the divisions that have marked stimulus-response and sign-significate learning theories. Studies and ideas about response feedback and learning are examined, and conclusions about the present state of empirical knowledge and theory are drawn. Closed-loop theory, with its emphasis on feedback and error detection, has been centered mainly in engineering and biological fields, but it is now emerging with implications for learning. The usefulness of closed-loop theory for old and new behavioral phenomena is discussed. (2 p. ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1968 American Psychological Association.