The purpose of this book is to assess the status of behavioral research and theory in mental deficiency. Part I is devoted mainly to theory, and Part II includes empirical findings categorized according to conventional areas of investigation. Some repetition of materials is intentional since the theoretical treatment must rely upon experimental results and, therefore, should be cited at that point. The summaries of empirical findings include much of the same material, which appears in the interest of the reader since this provides a complete review of research fairly divorced from theory. In the main, the theoretical treatments are extensions of those developed to explain the behavior of the normal organism. In some instances, however, modification of the existing theory is far-reaching. Most of the research upon which this book is based has been conducted within the past decade or so. The theories, as applied to mental deficiency, are of recent origin. The reader will find little formal attention to the history of mental deficiency, parent adjustment problems, administrative matters, social welfare issues, and other materials which are usually included in a book on mental deficiency. Rather we have attempted to come to grips with the basic problem, the behavior of the inadequate organism.
The problem of nomenclature is largely ignored. The reader will find the population referred to as mental defectives, mental retardates, mentally deficients, etc. How a "thing" is called is of little consequence. The defining operations are of central importance and the scientist is well aware of this. A term may have undesirable emotional connotations, but changing the term is only a temporary remedial measure. Some terms used to establish cate-