Piagetian stage IV search errors with an object that is directly accessible both visually and manually.

Previous work has shown that infants make the Piagetian stage IV error when the object is covered by a transparent occluder. However, it is not clear whether this happens because nine-month-old infants' failure to understand the identity of hidden objects extends to visible objects, or whether they are puzzled by object relationships involving transparency. Nine-month-old infants were presented with one of three different stage IV tasks in which the object was visible and uncovered at the second location. Stage IV errors were obtained with the object visible, but only when a covered place was provided at the first location. It is concluded that this result is stronger evidence that the stage IV error is not simply a hidden-object phenomenon, and that it may be best explained by taking account of infants' functional place knowledge, as well as their knowledge of object identity.