Child: care, health and development, 1987, 13, 247-255 Accelerated development of object permanence in Down's syndrome infants CAROL F, PASNAK Child Development Centre of Northern Virginia, Falls Church, Virginia and ROBERT PASNAK George Mason University, 4400 University Drive, Fairfax, VA 22030, USA Aeeepted for publieation 4 February 1987 Summary Six infants with Down's syndrome, aged 3-19 months, were taught to solve object permanence problems. The instruction took place in the infants' homes and in a child development centre, and was conducted both by parents and by a child psychologist. Object permanence tasks ranging over stages 3-6 of the sensorimotor period of intelligence were utilized in the intervention, which lasted for up to 8 months. The infants were able to progress rather rapidly on these tasks. When the instruction was terminated most had mastered multiple visible displacements, which index the fifth stage of sensori- motor intelligence. The development of object permanence proceeds in a normal sequence for Down's syndrome (DS) infants, but there is a substantial lag (Gibson 1978, Morss 1983). It is difficult to assess precisely the extent of this lag, given the small samples and the variability of the DS infants available to researchers, but it is not small, Morss (1983) reported that the eight DS infants he studied mastered the fourth stage of object permanence at an average age of 21-3 months, and the fifth at 24-2 months. Mervis & Cardoso-Martins (1984) reported mastery of the fifth stage at 22-8 months and entrance to the sixth at 23-8 months for their sample of four DS infants. For normal infants, mastery of the fourth stage is usually expected by 12 months and the transition between stages 5 and 6 at 18 months, although some researchers have reported much lower averages (Kramer et al. 1975, Miller et al. 1970, Triana & Pasnak 1986). Sensorimotor intelligence, as measured by object permanence, is an important index of mental development during the first 2 years of life. Woodward (1963) found, for a very large sample, that when IOs were below 50, problem solving ability, at least as measured by Piaget's 247