Longitudinal development of object permanence in mentally retarded children: an exploratory study

Monthly testing on a series of Piaget object tasks was carried out on 1- to 6-year-old profoundly, severly, and moderately retarded children. Forty nine subjects were followed for 1 to 1.5 years or to criterion; 18 subjects were followed for shorter periods. Three general patterns occurred among the noncriterion subjects with approximately equeal frequency: (a) little or no change, (b) marked variability, and (c) relatively steady upward change from month to month. Criterion and upward subjects skipped certain substages about one-half of the time. Degree of retardation, CA, and diagnostic concomitants of these observations were discussed.