Evidence for dimensional independence in short-term memory of retarded individuals.

This experiment was designed to assess the relative importance of dimensional similarity between test and interpolated problems and absolute difficulty of interpolated material as variables influencing short-term retention in the discrimination learning of retarded persons. Twenty moderate-to-borderline retarded individuals were taught a mixed series of two-trial discriminations consisting of: (a) relatively easy multidimensional ("junk") problems and (b) more difficult, form-relevant dotpattern discriminations. Test problems and interpolations were either dimensionally similar (both junk or both dot-pattern problems) or dissimilar (train one type of problem, interpolate the other). The major finding was that short-term forgetting occurred only when test and interpolated stimuli were dimensionally similar. Absolute difficulty of interpolations had no effect on retention. These results were interpreted as supporting Fisher and Zeaman's (1973) assumption of dimensional independence of memory processes in retarded persons. A secondary finding was that performance on dot-pattern discriminations varied with intelligence.