Piaget explains the stage IV error as a failure to assimilate the new place of hiding rather than a forgetting of it. His hypothesis predicts that the likelihood of error should not vary with the length of the delay interval. Nine-month-old infants delayed 0, 1, 3, or 7 seconds before having the opportunity to search. Infants in all conditions, save 0-seconds, were likely to err. While Piaget's hypothesis was not supported by the results of the 0-second condition, subsequent analyses of the data provided some support for Piaget's hypothesis. (Author)