Active perception can be used to facilitate perception of the rigid motion of either 3D or 4D objects projected to a lower dimension. The perspective on 3D rotating objects can be actively adjusted to place the axis of rotation so that the 2D motion in a frontoparallel plane is rigid. Likewise, the perspective on 4D rotating objects can be actively adjusted to make the invariant plane frontoparallel, rendering the 2D display static and therefore rigid. Although such active perception is not required to judge the rigidity of 3D rotating objects, we asked can the rigidity of 4D objects be judged and if so, whether active perception is required. Naive observers were trained to use the above active methods to judge displays of rotating objects and then they were tested in judging whether motion was rigid or non-rigid and of 3D or 4D objects. Subsequently, observers were tested in the same manner, but allowing only passive viewing from multiple perspectives excluding those yielding 2D rigid motion. The expectation was that active perception would allow more rapid and accurate judgments of the rigidity of both 3D and 4D objects, but that passive viewing would only allow accurate judgment of 3D objects, even after extensive training and practice. The results indicate that active visualization methods are indeed required to allow perceptual access to the structure and motion of 4D objects.