Infants' Sensitivity to Relative Size Information for Distance

Five-, 51/2-, and 7-month-old infants were tested for sensitivity to relative size as distance information. Infants viewed two equidistant objects that were identical except in size. Reaching was observed as a measure of the perceived relative distances of the two objects. Infants 51/2 months old and 7 months old gave clear evidence of sensitivity to relative size. Under monocular viewing conditions, both groups showed a preference to reach for the larger object of the pair. Under binocular viewing conditions, no difference in number of reaches for the large and small objects was found for either group. The lack of a reaching preference in the binocular condition suggests that the reaching preference observed in the monocular condition was due to the perceived spatial locations of the objects and not to a preference to reach for the larger object without regard to distance. Infants 5 months old gave no evidence of sensitivity to relative size. The finding that 51/2- and 7-month-olds are sensitive to relative size and the failure to find such sensitivity in 5-month-olds is consistent with results from other studies on infants' sensitivity to pictorial depth cues.