We assessed the effect on performance of shifting from a perceptual area judgment situation, in which the physical quantity to be judged (the area) is present in the stimulus, to a situation in which it is not present in the stimulus. Adults, 9-year-olds, and 5-year-olds were shown combinations of horizontal and vertical lines of various sizes, presented on the same wall or on different walls, and asked to estimate the corresponding area. The following main results were obtained (a) When width and height information items were completely separated, 5- and 9-year-old children gave the same weight to both dimensions in their estimations; (b) when width and height information items were on two different walls, adults gave a greater weight to the larger dimension; (c) when width and height were joined, 9-year-old children gave a greater weight to the larger dimension but when they were separated, they did not.