Familial Mental Retardation: A Continuing Dilemma
Authors: Zigler Edward 
Published: October 2006

The heterogeneous nature of mental retardation, as well as certain common practices of workers in the area, has resulted in a variety of conceptual ambiguities. Considerable order could be brought to the area if, instead of viewing all retardates as a homogeneous group arbitrarily defined by some I.Q. score, workers would clearly distinguish between the group of retardates known to suffer from some organic defect and the larger group of retardates referred to as familial retardates. It is the etiology of familial retardation that currently constitutes the greatest mystery.
A number of authorities have emphasized the need for employing recent polygenic models of inheritance in an effort to understand the familial retardate. While appreciating the importance of environment in affecting the distribution determined by genetic inheritance, these workers have argued that familial retardates are not essentially different from individuals of greater intellect, but represent, rather, the lower portion of the intellectual curve which reflects normal intellectual variability. As emphasized by the two-group approach, retardates with known physiological or organic defect are viewed as presenting a quite different etiological problem. The familial retardate, on the other hand, is seen as a perfectly normal expression of the population gene pool, of slower and more limited intellectual development than the individual of average intellect.
This view generates the proposition that retardates and normals at the same general cognitive level—that is, of the same mental age—are similar in respect to their cognitive functioning. However, such a proposition runs headlong into findings that retardates and normals of the same mental age often differ in performance. Such findings have bolstered what is currently the most popular theoretical approach to retarded functioning—namely, the view that all retardates suffer from some specific defect which inheres in mental retardation and thus makes the retardate immutably "different" from normals, even when the general level of intellectual development is controlled. While these defect or difference approaches, as exemplified in the work of Luria, Spitz, Ellis, and Lewin and Kounin, dominate the area of mental retardation, the indirect, and therefore equivocal, nature of the evidence of these workers has generated considerable controversy.
In contrast to this approach, the general developmental position has emphasized systematic evaluation of the role of experiential, motivational, and personality factors. As a central thesis, this position asserts that performance on experimental and real-life tasks is never the single inexorable product of the retardate's cognitive structure but, rather, reflects a wide variety of relatively nonintellective factors which greatly influence the general adequacy of performance. Thus, many of the reported behavioral differences between normals and retardates of the same mental age are seen as products of motivational and experiential differences between these groups, rather than as the result of any inherent cognitive deficiency in the retardates. Factors thought to be of particular importance in the behavior of the retardate are social deprivation and the positive- and negative-reaction tendencies to which such deprivation gives rise; the high number of failure experiences and the particular approach to problem-solving which they generate; and atypical reinforcer hierarchies.
There is little question that we are witnessing a productive, exciting, and perhaps inevitably chaotic period in the history of man's concern with the problem of mental retardation. Even the disagreements that presently exist must be considered rather healthy phenomena. These disagreements will unquestionably generate new knowledge which, in the hands of practitioners, may become the vehicle through which the performance of children, regardless of intellectual level, may be improved.