The development of conservation of size

It was pointed out that the questions used in many Piagetian experiments on the conservations and concrete operations are ambiguous, e.g., “Which is bigger?” means either “Which looks bigger?” or “Which is really bigger?” The development of conservation of size was investigated in a series of experiments in which illusory size changes were created in a variety of ways. On successive trials a stimulus item was made first to look bigger and then to look smaller than another stimulus item. Three experiments required correct differential responses to the questions “Which looks bigger?” and “Which is really bigger?” and one experiment required that the question “Which is bigger?” be interpreted as a question about real size. The experiments showed (1) that by about five years of age a majority of children are capable of a distinction between real and phenomenal size which is not at all task specific, and (2) that children under seven tend to construe questions containing the word “bigger” as questions about phenomenal size, unless feedback information forces a “reality” interpretation. The data suggest that early stages of development are not amenable to study by traditional Piagetian procedures, which do not elicit the processes under investigation in the younger Ss. It was proposed that what has to be explained in accounting for the conservations is the emergence of a general distinction between real and phenomenal properties of objects.